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MySQL (TM) is a very fast, multi-threaded, multi-user, and
robust SQL (Structured Query Language) database
server. MySQL is intended for mission-critical, heavy load production systems as
well as for embedding into mass-deployed software. MySQL is a
trademark of MySQL AB.
MySQL has Dual licensing, you can use MySQL free of charge under
the GNU GENERAL PUBLIC LICENSE (http://www.gnu.org/licenses/). You can
also purchase commercial MySQL licenses from MySQL AB if you do not
wish to be bound by the terms of the GPL. See section 1.4
MySQL Support and Licensing.
The MySQL web site (http://mysql.com/) provides the latest information about MySQL.
The following list describes some useful sections of the manual:
IMPORTANT:
Reports of errors (often called bugs), as well as questions and comments,
should be sent to the mailing list at mysql@lists.mysql.com. See section 1.6.2.3
How to Report Bugs or Problems. The mysqlbug script should be
used to generate bug reports. For source distributions, the
mysqlbug script can be found in the `scripts' directory.
For binary distributions, mysqlbug can be found in the
`bin' directory. If you have found a sensitive security bug in MySQL,
you should send an e-mail to security@mysql.com.
This is the MySQL reference manual; it documents MySQL Version 4.0.1-alpha. Being a reference manual, it does not provide general instruction on SQL or relational database concepts.
As MySQL is work in progress, the manual gets updated frequently. The most recent version of this manual is available at http://mysql.com/documentation/ in many different formats, currently there are Texinfo, plain text, Info, HTML, PostScript, and PDF versions.
The primary document is the Texinfo file. The HTML version is produced
automatically using a modified version of texi2html. The plain text
and Info versions are produced with makeinfo. The Postscript
version is produced using texi2dvi and dvips. The PDF
version is produced with pdftex.
If you have a hard time finding information in the manual, you can try our searchable PHP version at http://mysql.com/doc/.
If you have any suggestions concerning additions or corrections to this manual, please send them to the manual team at docs@mysql.com.
This manual is written and maintained by David Axmark, Michael (Monty) Widenius, Jeremy Cole, Arjen Lentz, and Paul DuBois. For other contributors, see section C Credits.
The copyright (2001) to this manual is owned by the Swedish company
MySQL AB. See section 1.4.2
Copyrights and Licenses Used by MySQL.
This manual uses certain typographical conventions:
constant
mysqladmin works, invoke it with the
--help option.''
When commands are shown that are meant to be executed by a particular
program, the program is indicated by a prompt shown before the command. For
example, shell> indicates a command that you execute from your
login shell, and mysql> indicates a command that you execute
from the mysql client program:
shell> type a shell command here mysql> type a mysql command here
Shell commands are shown using Bourne shell syntax. If you are using a
csh-style shell, you may need to issue commands slightly
differently. For example, the sequence to set an environment variable and run a
command looks like this in Bourne shell syntax:
shell> VARNAME=value some_command
For csh, you would execute the sequence like this:
shell> setenv VARNAME value shell> some_command
Often database, table, and column names must be substituted into commands. To
indicate that such substitution is necessary, this manual uses
db_name, tbl_name and col_name. For
example, you might see a statement like this:
mysql> SELECT col_name FROM db_name.tbl_name;
This means that if you were to enter a similar statement, you would supply your own database, table, and column names, perhaps like this:
mysql> SELECT author_name FROM biblio_db.author_list;
SQL statements may be written in uppercase or lowercase. When this manual
shows a SQL statement, uppercase is used for particular keywords if those
keywords are under discussion (to emphasize them) and lowercase is used for the
rest of the statement. For example, you might see the following in a discussion
of the SELECT statement:
mysql> SELECT count(*) FROM tbl_name;
On the other hand, in a discussion of the COUNT() function, the
same statement would be written like this:
mysql> select COUNT(*) from tbl_name;
If no particular emphasis is intended, all keywords are written uniformly in uppercase.
In syntax descriptions, square brackets (`[' and `]') are used to indicate optional words or clauses:
DROP TABLE [IF EXISTS] tbl_name
When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (`|'). When one member from a set of choices may be chosen, the alternatives are listed within square brackets (`[' and `]'):
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
When one member from a set of choices must be chosen, the alternatives are listed within braces (`{' and `}'):
{DESCRIBE | DESC} tbl_name {col_name | wild}
MySQL, the most popular Open Source SQL database, is developed
and provided by MySQL AB. MySQL AB is a commercial company that
builds its business providing services around the MySQL database. See section 1.3
What Is MySQL AB.
The MySQL web site (http://mysql.com/) provides the latest information about MySQL and MySQL AB.
The official way to pronounce MySQL is ``My Ess Que Ell'' (not ``my sequel''), but we don't mind if you pronounce it as ``my sequel'' or in some other localised way.
We once started out with the intention of using mSQL to connect
to our tables using our own fast low-level (ISAM) routines. However, after some
testing we came to the conclusion that mSQL was not fast enough nor
flexible enough for our needs. This resulted in a new SQL interface to our
database but with almost the same API interface as mSQL. This API
was chosen to ease porting of third-party code.
The derivation of the name MySQL is not perfectly clear. Our base directory and a large number of our libraries and tools have had the prefix ``my'' for well over 10 years. However, Monty's daughter (some years younger) is also named My. Which of the two gave its name to MySQL is still a mystery, even for us.
The following list describes some of the important characteristics of MySQL. See section 1.5 MySQL 4.0 In A Nutshell.
FLOAT, DOUBLE, CHAR,
VARCHAR, TEXT, BLOB,
DATE, TIME, DATETIME,
TIMESTAMP, YEAR, SET, and
ENUM types. See section 6.2
Column Types.
INSERT to insert a subset of a table's columns; those columns
that are not explicitly given values are set to their default values.
SELECT and
WHERE parts of queries. For example: mysql> SELECT CONCAT(first_name, " ", last_name)
FROM tbl_name
WHERE income/dependents > 10000 AND age > 30;
GROUP BY and ORDER BY
clauses. Support for group functions (COUNT(),
COUNT(DISTINCT ...), AVG(), STD(),
SUM(), MAX() and MIN()).
LEFT OUTER JOIN and RIGHT OUTER
JOIN with ANSI SQL and ODBC syntax.
DELETE, INSERT, REPLACE, and
UPDATE return the number of rows that were changed (affected).
It is possible to return the number of rows matched instead by setting a
flag when connecting to the server.
SHOW command can be used to retrieve
information about databases, tables, and indexes. The EXPLAIN
command can be used to determine how the optimiser resolves a query.
ABS is a valid column name. The only restriction is that for a
function call, no spaces are allowed between the function name and the
`(' that follows it. See section 6.1.6
Is MySQL Picky About Reserved Words?.
CHAR or VARCHAR field. myisamchk, a very fast utility for table checking,
optimisation, and repair. All of the functionality of myisamchk
is also available through the SQL interface as well. See section 4
MySQL Database Administration.
--help or
-? options to obtain online assistance. This section addresses the questions ``How stable is MySQL?'' and ``Can I depend on MySQL in this project?'' We will try to clarify these issues and answer some important questions that concern many potential users. The information in this section is based on data gathered from the mailing list, which is very active in identifying problems as well as reporting types of use.
Original code stems back from the early 80s, providing a stable code base, and the ISAM table format remains backwards compatible. At TcX, the predecessor of MySQL AB, MySQL has worked in projects since mid-1996, without any problems. When MySQL was released to a wider public, we noticed that there were some pieces of ``untested code'' that were quickly found by the new users who made different types of queries from us. Each new release has had fewer portability problems (even though each new release has had many new features).
Each release of MySQL has been usable. There have only been problems when users try code from the ``gray zones.'' Naturally, new users don't know what the gray zones are; this section attempts to indicate those that are currently known. The descriptions mostly deal with Version 3.23 of MySQL. All known and reported bugs are fixed in the latest version, with the exception of those listed in the bugs section, which are things that are design-related. See section 1.7.5 Known Errors and Design Deficiencies in MySQL.
MySQL design is multi-layered with independent modules. Some of the newer modules are listed below with an indication of how well-tested each of them is:
InnoDB tables -- Gamma
InnoDB transactional table handler is a fairly
recent addition to MySQL, it appears to work well and is already
being used in some large, heavy load production systems.
BDB tables -- Gamma
Berkeley DB code is very stable, but we are still
improving the BDB transactional table handler interface in MySQL,
so it will take some time before this is as well tested as the other table
types.
FULLTEXT -- Beta
MyODBC 2.50 (uses ODBC SDK 2.5) -- Gamma
MyISAM tables -- Gamma
MyISAM table
handler that checks if the table was closed properly on open and executes an
automatic check/repair of the table if it wasn't.
MyISAM tables in MySQL 4.0 for faster insert
of many rows.
fcntl()). In these cases, you should
run mysqld with the --skip-locking flag. Problems
are known to occur on some Linux systems, and on SunOS when using NFS-mounted
file systems. MySQL AB provides high-quality support for paying customers, but the MySQL mailing list usually provides answers to common questions. Bugs are usually fixed right away with a patch; for serious bugs, there is almost always a new release.
MySQL Version 3.22 has a 4G limit on table size. With the new
MyISAM table type in MySQL Version 3.23, the maximum table size is
pushed up to 8 million terabytes (2 ^ 63 bytes).
Note, however, that operating systems have their own file size limits. Here are some examples:
| Operating System | File Size Limit |
| Linux-Intel 32 bit | 2G, 4G or more, depends on Linux version |
| Linux-Alpha | 8T (?) |
| Solaris 2.5.1 | 2G (possible 4G with patch) |
| Solaris 2.6 | 4G |
| Solaris 2.7 Intel | 4G |
| Solaris 2.7 ULTRA-SPARC | 8T (?) |
On Linux 2.2 you can get bigger tables than 2G by using the LFS patch for the ext2 file system. On Linux 2.4 there exists also patches for ReiserFS to get support for big files.
This means that the table size for MySQL is normally limited by the operating system.
By default, MySQL tables have a maximum size of about 4G. You can check the
maximum table size for a table with the SHOW TABLE STATUS command
or with the myisamchk -dv table_name. See section 4.5.6
SHOW Syntax.
If you need bigger tables than 4G (and your operating system supports this),
you should set the AVG_ROW_LENGTH and MAX_ROWS
parameter when you create your table. See section 6.5.3
CREATE TABLE Syntax. You can also set these later with
ALTER TABLE. See section 6.5.4
ALTER TABLE Syntax.
If your big table is going to be read-only, you could use
myisampack to merge and compress many tables to one.
myisampack usually compresses a table by at least 50%, so you can
have, in effect, much bigger tables. See section 4.7.4
myisampack, The MySQL Compressed Read-only Table Generator.
You can go around the operating system file limit for MyISAM
data files by using the RAID option. See section 6.5.3
CREATE TABLE Syntax.
Another solution can be the included MERGE library, which allows you to handle a collection of identical tables as one. See section 7.2 MERGE Tables.
MySQL itself has no problems with Year 2000 (Y2K) compliance:
2069; all 2-digit years are regarded to be in the range
1970 to 2069, which means that if you store
01 in a year column, MySQL treats it as
2001.
YEAR column type can
store years 0 and 1901 to 2155 in 1
byte and display them using 2 or 4 digits. You may run into problems with applications that use MySQL in a way that is
not Y2K-safe. For example, many old applications store or manipulate years using
2-digit values (which are ambiguous) rather than 4-digit values. This problem
may be compounded by applications that use values such as 00 or
99 as ``missing'' value indicators.
Unfortunately, these problems may be difficult to fix, because different applications may be written by different programmers, each of whom may use a different set of conventions and date-handling functions.
Here is a simple demonstration illustrating that MySQL doesn't have any problems with dates until the year 2030:
mysql> DROP TABLE IF EXISTS y2k;
Query OK, 0 rows affected (0.01 sec)
mysql> CREATE TABLE y2k (date date,
date_time datetime,
time_stamp timestamp);
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO y2k VALUES
-> ("1998-12-31","1998-12-31 23:59:59",19981231235959),
-> ("1999-01-01","1999-01-01 00:00:00",19990101000000),
-> ("1999-09-09","1999-09-09 23:59:59",19990909235959),
-> ("2000-01-01","2000-01-01 00:00:00",20000101000000),
-> ("2000-02-28","2000-02-28 00:00:00",20000228000000),
-> ("2000-02-29","2000-02-29 00:00:00",20000229000000),
-> ("2000-03-01","2000-03-01 00:00:00",20000301000000),
-> ("2000-12-31","2000-12-31 23:59:59",20001231235959),
-> ("2001-01-01","2001-01-01 00:00:00",20010101000000),
-> ("2004-12-31","2004-12-31 23:59:59",20041231235959),
-> ("2005-01-01","2005-01-01 00:00:00",20050101000000),
-> ("2030-01-01","2030-01-01 00:00:00",20300101000000),
-> ("2050-01-01","2050-01-01 00:00:00",20500101000000);
Query OK, 13 rows affected (0.01 sec)
Records: 13 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM y2k;
+------------+---------------------+----------------+
| date | date_time | time_stamp |
+------------+---------------------+----------------+
| 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 |
| 1999-01-01 | 1999-01-01 00:00:00 | 19990101000000 |
| 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 |
| 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 |
| 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 |
| 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 |
| 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 |
| 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 |
| 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 |
| 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 |
| 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 |
| 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 |
| 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 |
+------------+---------------------+----------------+
13 rows in set (0.00 sec)
This shows that the DATE and DATETIME types will
not give any problems with future dates (they handle dates until the year 9999).
The TIMESTAMP type, which is used to store the current time, has
a range up to only 2030-01-01. TIMESTAMP has a range
of 1970 to 2030 on 32-bit machines (signed value). On
64-bit machines it handles times up to 2106 (unsigned value).
Even though MySQL is Y2K-compliant, it is your responsibility to provide unambiguous input. See section 6.2.2.1 Y2K Issues and Date Types for MySQL's rules for dealing with ambiguous date input data (data containing 2-digit year values).
MySQL AB is the company of the MySQL founders and main
developers. MySQL AB was originally established in Sweden by David Axmark, Allan
Larsson and Michael Monty Widenius.
All the developers of the MySQL server are employed by the company. We are a virtual organisation with people in a dozen countries around the world. We communicate extensively over the net every day with each other and with our users, supporters and partners.
We are dedicated to developing MySQL and spreading our database to new users. MySQL AB owns the copyright to the MySQL source code, the MySQL logo and trademark and this manual. See section 1.2 What Is MySQL.
The MySQL core values show our dedication to MySQL and Open Source.
We want MySQL to be:
MySQL AB and the people at MySQL AB:
The MySQL web site (http://mysql.com/) provides the latest information about MySQL and MySQL AB.
One of the most common questions we encounter is: ``How can you make a living from something you give away for free?'' This is how.
MySQL AB makes money on support, services, commercial licenses and royalties, and we use these revenues to fund product development and to expand the MySQL business.
The company has been profitable since its inception. In October 2001, we accepted venture financing from leading Scandinavian investors and a handful of business angels. This investment is used to solidify our business model and build a basis for sustainable growth.
MySQL AB is run and owned by the founders and main developers of the MySQL
database. The developers are committed to giving support to customers and other
users in order to stay in touch with their needs and problems. All our support
is given by qualified developers. Really tricky questions are answered by
Michael Monty Widenius, principal author of the MySQL server. See
section 1.4.1
Support Offered by MySQL AB.
To order support at various levels, please visit the order section at https://order.mysql.com/. If you have restricted access to the Internet, please contact our sales staff at sales@mysql.com.
MySQL AB delivers MySQL and related training worldwide. We offer both open courses and In-House courses tailored to specific needs of your company. MySQL Training is also available through our partners, the Authorised MySQL Training Centers.
Our training material uses the same example databases as our documentation and our sample applications, and it is always updated to reflect the latest MySQL version. Our trainers are backed by the development team to guarantee the quality of the training and the continuous development of the course material. This also ensures that no questions raised during the courses remain unanswered.
Attending our training courses will enable you to achieve your goals related to your MySQL applications. You will also:
If you are interested in our training as a potential participant or training partner, please visit the training section at http://mysql.com/training/. If you have restricted access to the Internet, please contact our training staff at training@mysql.com.
We plan to release the MySQL Certification Program in 2002, for details see http://mysql.com/training/certification.html. If you would like to be kept informed about the MySQL Certification Program, please e-mail certification@mysql.com.
MySQL AB and its Authorised Partners offer consulting services to users of MySQL and to those who embed MySQL in their own software, all over the world.
Our consultants can help you design and tune your databases, construct efficient queries, tune your platform for optimal performance, resolve migration issues, set up replication, build robust transactional applications, and more. We also help customers embed MySQL in their products and applications for large-scale deployment.
Our consultants work in close collaboration with our development team which ensures the technical quality of our professional services. Consulting assignments range from 2-day power start sessions to projects that span weeks and months. Our expertise does not only cover MySQL, but extends into programming and scripting languages such as PHP, Perl and more.
If you are interested in our consulting services or want to become a consulting partner, please visit the consulting section of our web site at http://mysql.com/consulting/. If you have restricted access to the Internet, please contact our consulting staff at consulting@mysql.com.
The MySQL database is released under the GNU General Public
License (GPL). This means that MySQL can be used free of
charge under the GPL. If you do not want to be bound by the GPL terms (like the
requirement that your own application becomes GPL as well), you may purchase a
commercial license for the same product from MySQL AB at https://order.mysql.com/. Since MySQL AB
owns the copyright to the MySQL server, we are able to employ Dual
Licensing which means that the same product is available both under GPL
and under a commercial license. This does not in any way affect the Open
Source commitment of MySQL AB. For details about when a commercial
license is required, please see section 1.4.3
MySQL Server Licenses.
We also sell commercial licenses of third-party Open Source GPL software that
adds value to MySQL. A good example is the InnoDB transactional
table handler that offers ACID support, row-level locking, crash recovery,
multiversioning, foreign key support, and more.
MySQL AB has a worldwide partner program that covers training courses, support, consulting, solutions, publications plus reselling and distributing MySQL and related products. Partners get visibility on the http://mysql.com/ web site and the right to use special versions of the MySQL trademarks to identify their products and promote their business.
If you are interested in becoming a MySQL AB partner, please e-mail to partner@mysql.com.
The word MySQL and the MySQL dolphin logo are trademarks of
MySQL AB. See section 1.4.4
MySQL AB Logos and Trademarks. These trademarks represent a significant
value that the MySQL founders have built over the years.
The MySQL web site (http://mysql.com/) is popular among developers and users. In October 2001, we served 10 million page views. Our visitors represent a group that makes purchase decisions and recommendations for both software and hardware. Twelve per cent of our visitors authorise purchase decisions, and only nine per cent are not involved in purchase decisions at all. More than 65% have made one or more online business purchase within the last half-year, and 70% plan to make one in the next months.
If you are interested in placing banner ads on our web site http://mysql.com/, please send an email to advertising@mysql.com.
The MySQL web site (http://mysql.com/) provides the latest information about MySQL and MySQL AB.
For press service and inquiries not covered in our News releases (http://mysql.com/news/), please e-mail to press@mysql.com.
If you have a valid support contract with MySQL AB; you will get timely, precise answers to your technical questions about MySQL. For more information, see section 1.4.1 Support Offered by MySQL AB. You can order your support contract at https://order.mysql.com/, or send an email to sales@mysql.com.
For information about MySQL training, please visit the training section at http://mysql.com/training/. If you have restricted access to the Internet, please contact the MySQL AB training staff at training@mysql.com. See section 1.3.1.2 Training and Certification.
For information on the MySQL Certification Program, please see http://mysql.com/training/certification.html. If you would like to be kept informed about the MySQL Certification Program, please e-mail certification@mysql.com. See section 1.3.1.2 Training and Certification.
If you're interested in consulting, please visit the consulting section at http://mysql.com/consulting/. If you have restricted access to the Internet, please contact the MySQL AB consulting staff at consulting@mysql.com. See section 1.3.1.3 Consulting.
Commercial licenses may be purchased online at https://order.mysql.com/. There you will also find information on how to fax your purchase order to MySQL AB. If you have questions regarding licensing or you want a quote for a high-volume license deal, please fill in the contact form on our web site (http://mysql.com/) or send an email to licensing@mysql.com (for licensing questions) or to sales@mysql.com (for sales inquiries). See section 1.4.3 MySQL Server Licenses.
If you represent a business that is interested in partnering with MySQL AB, please send e-mail to partner@mysql.com. See section 1.3.1.5 Partnering.
If you are interested in placing a banner advertisement on the MySQL web site (http://mysql.com/), please send e-mail to advertising@mysql.com. See section 1.3.1.6 Advertising.
For more information on the MySQL trademark policy, refer to http://mysql.com/company/trademark.html or email trademark@mysql.com. See section 1.4.4 MySQL AB Logos and Trademarks.
If you are interested in any of the MySQL AB jobs listed in our jobs section (http://mysql.com/development/jobs/), please send an e-mail to jobs@mysql.com. Please do not send your cv as an attachment, but rather as plain text at the end of your email.
For general discussion amongst our many users, please direct your attention to the appropriate mailing list. See section 1.6.2 MySQL Mailing Lists.
Reports of errors (often called bugs), as well as questions and comments, should be sent to the mailing list at mysql@lists.mysql.com. If you have found a sensitive security bug in MySQL, you should send an e-mail to security@mysql.com. See section 1.6.2.3 How to Report Bugs or Problems.
If you have benchmark results that we can publish, please contact us at benchmarks@mysql.com.
If you have any suggestions concerning additions or corrections to this manual, please send them to the manual team at docs@mysql.com.
For questions or comments about the workings or content of the MySQL web site (http://mysql.com/), please send e-mail to webmaster@mysql.com.
Questions about the MySQL Portals (http://mysql.com/portal/) may be sent to portals@mysql.com.
MySQL AB has a privacy policy, which can be read at http://mysql.com/company/privacy.html. For any queries regarding this policy, please e-mail privacy@mysql.com.
For all other inquires, please send e-mail to info@mysql.com.
This section describes MySQL support and licensing arrangements:
Technical support from MySQL AB means individualised answers to your unique problems direct from the software engineers who code the MySQL database engine.
We try to take a broad and inclusive view of technical support. Almost any problem involving MySQL is important to us if it's important to you. Typically customers seek help on how to get different commands and utilities to work, remove performance bottlenecks, restore crashed systems, understand operating system or networking impacts on MySQL, set-up best practices for backup and recovery, utilise APIs, etc. Our support covers only the MySQL server and our own utilities, not third-party products that access MySQL, though we try to help with these where we can.
Detailed information about our various support options is given at https://order.mysql.com/ where support contracts can also be ordered online. If you have restricted access to the Internet, contact our sales staff at sales@mysql.com.
Technical support is like life insurance. You can live happily without it for years, but when your hour arrives it becomes critically important, yet it's too late to buy it! If you use MySQL for important applications and encounter sudden troubles, it might take too long to figure out all the answers yourself. You may need immediate access to the most experienced MySQL troubleshooters available, those employed by MySQL AB.
MySQL AB owns the copyright to the MySQL source code, the MySQL
logos and trademarks and this manual. See section 1.3
What Is MySQL AB. There are several different licenses relevant to the MySQL
distribution:
mysqlclient
library is licensed under the LGPL and the programs in the
`client' directory are under the GPL. Each file states
at the beginning which license it is under.
getopt library, are covered
by the ``GNU LESSER GENERAL PUBLIC LICENSE.'' See section I
GNU LESSER GENERAL PUBLIC LICENSE. The aim of this is to make it possible
to add MySQL support (client side, i.e. the ability to connect to a MySQL
server) into commercial products without a license.
readline library,
are covered by the ``GNU GENERAL PUBLIC LICENSE.'' See section H GNU
GENERAL PUBLIC LICENSE. The text of this license can also be found as the
file `COPYING' in the distributions.
regexp library) are covered by
a Berkeley-style copyright.
For information about how the MySQL licenses work in practice, please refer to section 1.4.3 MySQL Server Licenses. Also see section 1.4.4 MySQL AB Logos and Trademarks.
The MySQL server is released under the GNU General Public License (GPL), which probably is the best known Open Source license. The formal terms of the GPL license can be found at http://www.gnu.org/licenses/. See also http://www.gnu.org/licenses/gpl-faq.html.
Since the MySQL server is released under the GPL, it may often be used for free, but for certain uses you may want or need to buy commercial licenses from MySQL AB at https://order.mysql.com/.
Older versions of MySQL (3.22 and earlier) are subject to a more strict license (http://mysql.com/support/arrangements/mypl.html). See the documentation of the specific version for information.
Please note that the use of the MySQL server under commercial license, GPL or the old MySQL license does not automatically give you the right to use MySQL AB trademarks. See section 1.4.4 MySQL AB Logos and Trademarks.
The GPL license is contagious in the sense that when a program is linked to a GPL program the resulting product must also be released under GPL lest you break the license terms and forfeit your right to use the GPL program altogether.
You need a commercial license:
If you require a license, you will need one for each installation of the MySQL server. This covers any number of CPUs on a machine, and there is no artificial limit on the number of clients that connect to the server in any way.
To purchase commercial licenses and support, please visit the order section of our web site at https://order.mysql.com/. If you have restricted access to the Internet, please contact our sales staff at sales@mysql.com.
You can use the MySQL server for free under the GPL:
GNU Lesser General Public
License. The formal terms of the LGPL license can be found at http://www.gnu.org/licenses/. However,
the mysql command-line client does include code from the GNU
readline library that is under the GPL.
announce mailing list so that they can be aware of critical
issues that may be relevant for their MySQL installations. Note that even if
an ISP does not have a commercial license for MySQL, they should at least give
their customers read access to the source of the MySQL installation so that
the customers can verify that it is patched correctly.
If your use of MySQL does not require a commercial license, we encourage you to purchase support from MySQL AB anyway. This way you contribute towards MySQL development and also gain immediate advantages for yourself. See section 1.4.1 Support Offered by MySQL AB.
If you use MySQL in a commercial context such that you profit by its use, we ask that you further the development of MySQL by purchasing some level of support. We feel that if MySQL helps your business, it is reasonable to ask that you help MySQL. (Otherwise, if you ask us support questions, you are not only using for free something into which we've put a lot a work, you're asking us to provide free support, too.)
Many users of the MySQL database want to display the MySQL AB dolphin logo on
their web sites, on their books or boxed products. We welcome and encourage this
although it should be noted that the word MySQL and the MySQL
dolphin logo are trademarks of MySQL AB and may only be used as stated in our
trademark policy at http://mysql.com/company/trademark.html.
The MySQL dolphin logo was designed by the Finnish advertising agency Priority in 2001. The dolphin was chosen as a suitable symbol for the MySQL database since it is a smart, fast and lean animal, effortlessly navigating oceans of data. We also happen to like dolphins.
The original MySQL logo may only be used by representatives of MySQL AB and by those having a written agreement allowing them to do so.
We have designed a set of special Conditional Use logos that may be downloaded from our web site at http://mysql.com/downloads/logos.html and used on third party web sites without written permission from MySQL AB. The use of these logos is not entirely unrestricted but as the name implies subject to our trademark policy that is also available on our web site. You should read through the trademark policy if you plan to use them. The requirements are basically:
Contact us at trademark@mysql.com to inquire about special arrangements to fit your needs.
In the following cases you need a written permission from MySQL AB before using MySQL logos:
Out of legal and commercial reasons we have to monitor the use of MySQL trademarks on products, books etc. We will usually require a fee for displaying MySQL AB logos on commercial products, since we think it is reasonable that some of the revenue is returned to fund further development of the MySQL database.
MySQL partnership logos may only be used by companies and persons having a written partnership agreement with MySQL AB. Partnerships include certification as a MySQL trainer or consultant. Please see See section 1.3.1.5 Partnering.
MySQL
in Printed Text or PresentationsMySQL AB welcomes references to the MySQL database, but note that the word
MySQL is a trademark of MySQL AB. Because of this, you should
append the trademark symbol TM to the first or most prominent use
of the word MySQL in a text and where appropriate use a statement that
MySQL is a trademark of MySQL AB. Please refer to our trademark
policy at http://mysql.com/company/trademark.html
for details.
MySQL in Company and Product NamesUse of the word MySQL in product or company names or in Internet
domain names is not allowed without written permission from MySQL AB.
Dateline: 16 October 2001, Uppsala, Sweden
Long promised by MySQL AB and long awaited by our users, MySQL 4.0 is now available in alpha version for download from http://mysql.com/ and our mirrors.
Main new features of MySQL 4.0 are geared towards our existing business and community users, enhancing MySQL as the solution for mission-critical, heavy load database systems. Other new features target the users of embedded databases.
The rollout of MySQL 4.0 will come in several steps, with the first version labelled 4.0.0 already containing most of the new features. Additional features will be incorporated into MySQL 4.0.1, 4.0.2 onwards; very probably within a couple of months, MySQL 4.0 will be labelled beta. Further new features will then be added in MySQL 4.1, which is targeted for alpha release in early 2002.
Users are not recommended to switch their production systems to MySQL 4.0 until it is released in beta version. However, even the initial release has passed our extensive test suite without any errors on any of the platforms we test on. Due to the large number of new features, we thus recommend MySQL 4.0 even in alpha form for development use, with the release schedule of MySQL 4.0 being such that it will reach stable state before the deployment of user applications now under development.
libmysqld makes MySQL suitable for a vastly expanded realm of
applications. Using the embedded MySQL server library, one can embed MySQL into
various applications and electronics devices, where the end user has no
knowledge of there actually being an underlying database. Embedded MySQL is
ideal for use behind the scenes in internet appliances, public kiosks, turn-key
hardware/ software combination units, high performance internet servers,
self-contained databases distributed on CD-ROM etc.
Many embedded MySQL users will benefit from the dual licensing scheme of MySQL, where besides the GPL license also commercial licensing is available for those not wishing to be bound by the GPL. The embedded MySQL library uses the same interface as the normal client library, so it is convenient and easy to use.
INSERTs, searching on packed indices,
creation of FULLTEXT indices as well as
COUNT(DISTINCT).
InnoDB is now offered as a feature of the
standard MySQL server, including full support for transactions
and row-level locking.
Secure Sockets
Layer (SSL), thus enabling secure traffic to MySQL
databases from, say, a Windows application residing outside the firewall.
migration from other database systems to
MySQL include TRUNCATE TABLE (like in Oracle) and
IDENTITY as a synonym for automatically incremented keys (like in
Sybase). Many users will also be happy to learn that MySQL now supports the
UNION statement, a long awaited standard SQL feature.
DELETE statements. By adding support for symbolic
linking to MyISAM on the table level (and not just
database level as before), as well as by enabling symlink handling by default
on Windows, we hope to show that we take enhancement requests seriously.
Functions like SQL_CALC_FOUND_ROWS and FOUND_ROWS()
makes it possible to know how many rows a query would have returned without a
LIMIT clause. For the upcoming MySQL 4.0 releases (4.0.1, 4.0.2 and onwards), expect the following features now still under development:
fail-safe replication; already in existing 4.0.0,
the LOAD DATA FROM MASTER command will soon automate slave setup.
The online backup will make it easy to add a new replication
slave without taking down the master, and have a very low performance penalty
on update-heavy systems.
FULLTEXT search properties of MySQL 4.0 enables the
use of FULLTEXT indexing of large text masses with both binary
and natural language searching logic. Users can customise minimal word length
and define their own stop word lists in any human language, enabling a new set
of applications to be built on MySQL.
key cache.
MySQL command
help in the client. Internally, through a new .frm file format for table definitions, MySQL 4.0
lays the foundation for the new features of MySQL 4.1, such as nested
subqueries, stored procedures, and foreign key
integrity rules, which form the top of the wish list for many of our
customers. Along with those, we will also include simpler additions, such as
multi-table UPDATE statements.
After those additions, critics of MySQL have to be more imaginative than ever in pointing out deficiencies in the MySQL Database Management System. For long already known for its stability, speed, and ease of use, MySQL will then match the requirement checklist of very demanding buyers.
The MySQL Portals (http://mysql.com/portal/) on our web site feature a diverse range of MySQL related information and links, designed to make it easy to find the things your need.
You may register as a user, which will allow you to comment and rate any items in the portals as well as submit your own contributions. By registering you may also choose to receive news letters from categories that you select.
Some of the current MySQL Portal categories:
This section introduces you to the MySQL mailing lists, and gives some guidelines as to how to use them. By subscribing to a mailing list, you will receive as emails all other postings on the list, and you will be able to send in your own questions and answers.
To subscribe to the main MySQL mailing list, send a message to the electronic mail address mysql-subscribe@lists.mysql.com.
To unsubscribe from the main MySQL mailing list, send a message to the electronic mail address mysql-unsubscribe@lists.mysql.com.
Only the address to which you send your messages is significant. The subject line and the body of the message are ignored.
If your reply address is not valid, you can specify your address explicitly.
Adding a hyphen to the subscribe or unsubscribe command word, followed by your
address with the `@' character in your address replaced by a
`='. For example, to subscribe your_name@host.domain,
send a message to
mysql-subscribe-your_name=host.domain@lists.mysql.com.
Mail to mysql-subscribe@lists.mysql.com or mysql-unsubscribe@lists.mysql.com is handled automatically by the ezmlm mailing list processor. Information about ezmlm is available at the ezmlm web site (http://www.ezmlm.org/).
To post a message to the list itself, send your message to
mysql@lists.mysql.com. However, please do not send mail
about subscribing or unsubscribing to mysql@lists.mysql.com, because any mail
sent to that address is distributed automatically to thousands of other users.
Your local site may have many subscribers to mysql@lists.mysql.com. If so, it may
have a local mailing list, so that messages sent from
lists.mysql.com to your site are propagated to the local list. In
such cases, please contact your system administrator to be added to or dropped
from the local MySQL list.
If you wish to have traffic for a mailing list go to a separate mailbox in
your mail program, set up a filter based on the message headers. You can use
either the List-ID: or Delivered-To: headers to
identify list messages.
The following MySQL mailing lists exist:
announce-subscribe@lists.mysql.com
announce
mysql-subscribe@lists.mysql.com
mysql
mysql-digest-subscribe@lists.mysql.com
mysql-digest
mysql list in digest form. That means you get all
individual messages, sent as one large mail message once a day.
bugs-subscribe@lists.mysql.com
bugs
mysqlbug script (if you are running on Windows, you should
include a description of the operating system and the MySQL version).
Preferably, you should test the problem using the latest stable or development
version of MySQL before posting! Anyone should be able to repeat the bug by
just using mysql test < script on the included test case. All
bugs posted on this list will be corrected or documented in the next MySQL
release! If there are only small code changes involved, we will also post a
patch that fixes the problem.
bugs-digest-subscribe@lists.mysql.com
bugs-digest
bugs list in digest form.
internals-subscribe@lists.mysql.com
internals
internals-digest-subscribe@lists.mysql.com
internals-digest
internals list.
java-subscribe@lists.mysql.com
java
java-digest-subscribe@lists.mysql.com
java-digest
java list.
win32-subscribe@lists.mysql.com
win32
win32-digest-subscribe@lists.mysql.com
win32-digest
win32 list.
myodbc-subscribe@lists.mysql.com
myodbc
myodbc-digest-subscribe@lists.mysql.com
myodbc-digest
myodbc list.
plusplus-subscribe@lists.mysql.com
plusplus
plusplus-digest-subscribe@lists.mysql.com
plusplus-digest
plusplus list.
msql-mysql-modules-subscribe@lists.mysql.com
msql-mysql-modules
msql-mysql-modules-digest-subscribe@lists.mysql.com
msql-mysql-modules-digest
msql-mysql-modules list. You subscribe or unsubscribe to all lists in the same way as described above.
In your subscribe or unsubscribe message, just put the appropriate mailing list
name rather than mysql. For example, to subscribe to or unsubscribe
from the myodbc list, send a message to myodbc-subscribe@lists.mysql.com
or myodbc-unsubscribe@lists.mysql.com.
If you can't get an answer for your questions from the mailing list, one option is to pay for support from MySQL AB, which will put you in direct contact with MySQL developers. See section 1.4.1 Support Offered by MySQL AB.
The following table shows some MySQL mailing in other languages than English. Note that these are not operated by MySQL AB, so we can't guarantee the quality on these.
mysql-france-subscribe@yahoogroups.com
A French mailing list
list@tinc.net A Korean mailing
list
subscribe mysql your@e-mail.address to this list.
mysql-de-request@lists.4t2.com
A German mailing list
subscribe mysql-de your@e-mail.address to this list.
You can find information about this mailing list at http://www.4t2.com/mysql/.
mysql-br-request@listas.linkway.com.br
A Portugese mailing list
subscribe mysql-br your@e-mail.address to this list.
mysql-alta@elistas.net A
Spanish mailing list
subscribe mysql your@e-mail.address to this list.
Before posting a bug report or question, please do the following:
If you can't find an answer in the manual or the archives, check with your local MySQL expert. If you still can't find an answer to your question, go ahead and read the next section about how to send mail to mysql@lists.mysql.com.
Writing a good bug report takes patience, but doing it right the first time saves time for us and for you. A good bug report containing a full test case for the bug will make it very likely that we will fix it in the next release. This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.
We encourage everyone to use the mysqlbug script to generate a
bug report (or a report about any problem), if possible. mysqlbug
can be found in the `scripts' directory in the source distribution, or,
for a binary distribution, in the `bin' directory under your MySQL
installation directory. If you are unable to use mysqlbug, you
should still include all the necessary information listed in this section.
The mysqlbug script helps you generate a report by determining
much of the following information automatically, but if something important is
missing, please include it with your message! Please read this section carefully
and make sure that all the information described here is included in your
report.
The normal place to report bugs and problems is mysql@lists.mysql.com. If you can make a
test case that clearly demonstrates the bug, you should post it to the bugs@lists.mysql.com list. Note that on
this list you should only post a full, repeatable bug report using the
mysqlbug script. If you are running on Windows, you should include
a description of the operating system and the MySQL version. Preferably, you
should test the problem using the latest stable or development version of MySQL
before posting! Anyone should be able to repeat the bug by just using
``mysql test < script'' on the included test case or run the
shell or perl script that is included in the bug report. All bugs posted on the
bugs list will be corrected or documented in the next MySQL
release! If there are only small code changes involved to correct this problem,
we will also post a patch that fixes the problem.
If you have found a sensitive security bug in MySQL, you should send an e-mail to security@mysql.com.
Remember that it is possible to respond to a message containing too much information, but not to one containing too little. Often people omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is: if you are in doubt about stating something, state it! It is a thousand times faster and less troublesome to write a couple of lines more in your report than to be forced to ask again and wait for the answer because you didn't include enough information the first time.
The most common errors are that people don't indicate the version number of the MySQL distribution they are using, or don't indicate what platform they have MySQL installed on (including the platform version number). This is highly relevant information, and in 99 cases out of 100 the bug report is useless without it! Very often we get questions like, ``Why doesn't this work for me?'' then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has been fixed already in newer MySQL versions. Sometimes the error is platform dependent; in such cases, it is next to impossible to fix anything without knowing the operating system and the version number of the platform.
Remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is MySQL-related. Most compilers are under development all the time and become better version by version. To determine whether or not your problem depends on your compiler, we need to know what compiler is used. Note that every compiling problem should be regarded as a bug report and reported accordingly.
It is most helpful when a good description of the problem is included in the bug report. That is, a good example of all the things you did that led to the problem and the problem itself exactly described. The best reports are those that include a full example showing how to reproduce the bug or problem. See section E.1.6 Making a test case when you experience table corruption.
If a program produces an error message, it is very important to include the message in your report! If we try to search for something from the archives using programs, it is better that the error message reported exactly matches the one that the program produces. (Even the case should be observed!) You should never try to remember what the error message was; instead, copy and paste the entire message into your report!
If you have a problem with MyODBC, you should try to generate a MyODBC trace file. See section 8.3.7 Reporting Problems with MyODBC.
Please remember that many of the people who will read your report will do so
using an 80-column display. When generating reports or examples using the
mysql command line tool, you should therefore use the
--vertical option (or the \G statement terminator) for
output that would exceed the available width for such a display (for example,
with the EXPLAIN SELECT statement; see the example below).
Please include the following information in your report:
mysqladmin version. mysqladmin can be
found in the `bin' directory under your MySQL installation directory.
uname -a.
mysqld died, you should also report the query that crashed
mysqld. You can usually find this out by running
mysqld with logging enabled. See section E.1.5
Using log files to find cause of errors in mysqld.
mysqldump --no-data db_name tbl_name1 tbl_name2 .... This is very
easy to do and is a powerful way to get information about any table in a
database that will help us create a situation matching the one you have.
SELECT statements,
you should always include the output of EXPLAIN SELECT ..., and
at least the number of rows that the SELECT statement produces.
The more information you give about your situation, the more likely it is that
someone can help you! For example, the following is an example of a very good
bug report (it should of course be posted with the mysqlbug
script): Example run using the mysql command line tool (note the
use of the \G statement terminator for statements whose output
width would otherwise exceed that of an 80-column display device): mysql> SHOW VARIABLES;
mysql> SHOW COLUMNS FROM ...\G
<output from SHOW COLUMNS>
mysql> EXPLAIN SELECT ...\G
<output from EXPLAIN>
mysql> FLUSH STATUS;
mysql> SELECT ...;
<A short version of the output from SELECT,
including the time taken to run the query>
mysql> SHOW STATUS;
<output from SHOW STATUS>
mysqladmin variables extended-status processlist
in your mail to provide some information of how your system is performing!
mysqldump and create a `README' file
that describes your problem. Create a compressed archive of your files using
tar and gzip or zip, and use
ftp to transfer the archive to ftp://support.mysql.com/pub/mysql/secret/.
Then send a short description of the problem to bugs@lists.mysql.com.
ftp to transfer it
to ftp://support.mysql.com/pub/mysql/secret/.
If the data are really top secret and you don't want to show them even to us,
then go ahead and provide an example using other names, but please regard this
as the last choice.
mysqld daemon and that you use to run any MySQL client programs.
The options to programs like mysqld and mysql, and
to the configure script, are often keys to answers and are very
relevant! It is never a bad idea to include them anyway! If you use any
modules, such as Perl or PHP, please include the version number(s) of those as
well.
mysqlaccess, the output of mysqladmin
reload, and all the error messages you get when trying to connect! When
you test your privileges, you should first run mysqlaccess. After
this, execute mysqladmin reload version and try to connect with
the program that gives you trouble. mysqlaccess can be found in
the `bin' directory under your MySQL installation directory.
parse error, please check your syntax closely!
If you can't find something wrong with it, it's extremely likely that your
current version of MySQL doesn't support the query you are using. If you are
using the current version and the manual at http://mysql.com/doc/ doesn't cover the
syntax you are using, MySQL doesn't support your query. In this case, your
only options are to implement the syntax yourself or e-mail mysql-licensing@mysql.com and ask
for an offer to implement it! If the manual covers the syntax you are using,
but you have an older version of MySQL, you should check the MySQL change
history to see when the syntax was implemented. In this case, you have the
option of upgrading to a newer version of MySQL. See section D MySQL
change history.
myisamchk or CHECK
TABLE and REPAIR TABLE. See section 4
MySQL Database Administration.
mysqld should never
crash a table if nothing killed it in the middle of an update! If you can find
the cause of mysqld dying, it's much easier for us to provide you
with a fix for the problem. See section A.1
How to Determine What Is Causing Problems.
If you are a support customer, please cross-post the bug report to mysql-support@mysql.com for higher priority treatment, as well as to the appropriate mailing list to see if someone else has experienced (and perhaps solved) the problem.
For information on reporting bugs in MyODBC, see section 8.3.4 How to Report Problems with MyODBC.
For solutions to some common problems, see See section A Problems and Common Errors.
When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarise the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem!
If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer.
Try to summarise the essential part of the question in your reply; don't feel obliged to quote the entire original message.
Please don't post mail messages from your browser with HTML mode turned on! Many users don't read mail with a browser!
This section describes how MySQL relates to the ANSI SQL standards. MySQL has many extensions to the ANSI SQL standards, and here you will find out what they are, and how to use them. You will also find information about functionality missing from MySQL, and how to work around some differences.
Our goal is to not, without a very good reason, restrict MySQL usability for any usage. Even if we don't have the resources to do development for every possible use, we are always willing to help and offer suggestions to people that is trying to use MySQL in new territories.
One of our main goals with the product is to continue to work towards ANSI 99
compliancy, but without sacrificing speed or reliability. We are not afraid to
add extensions to SQL or support for non-SQL features if this greatly increase
the usability of MySQL for a big part of our users. (The new
HANDLER interface in MySQL 4.0 is an example of this strategy. See
section 6.4.2
HANDLER Syntax.)
We will continue to support transactional and not transactional databases to satisfy both heavy web/logging usage and mission critical 24/7 usage.
MySQL was designed from the start to work with medium large databases (10-100 million rows / about 100 MB per table) on small computer systems. We will continue to extend MySQL to both work even better with terabyte size databases, but we are also doing work to make it possible to compile a reduced MySQL version that is more suitable for hand held devices and embedded usage. The compact design of MySQL makes both of these directions possible without any conflicts in the source tree.
We are currently not targeting real time support or clustered databases (even if you can already do a lot of things with our replication services).
We don't believe that one should have native XML support in the database, but will instead add the XML support our users request from us on the client side. We think it's better to keep the main server code as ``lean and clean'' as possible and instead develop libraries to deal with the complexity on the client side. This is part of the strategy mentioned above of not sacrificing speed or reliability in the server.
Entry level SQL92. ODBC levels 0-2.
We are aiming towards supporting the full ANSI SQL99 standard, but without concessions to speed and quality of the code.
If you start mysqld with the --ansi option, the
following behavior of MySQL changes:
|| is string concatenation instead of OR.
REAL will be a synonym for FLOAT instead of a
synonym of DOUBLE.
SERIALIZABLE. See
section 6.7.3
SET TRANSACTION Syntax. This is the same as using
--sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,
IGNORE_SPACE,SERIALIZE,ONLY_FULL_GROUP_BY.
MySQL includes some extensions that you probably will not
find in other SQL databases. Be warned that if you use them, your code will not
be portable to other SQL servers. In some cases, you can write code that
includes MySQL extensions, but is still portable, by using comments of the form
/*! ... */. In this case, MySQL will parse and execute the code
within the comment as it would any other MySQL statement, but other SQL servers
will ignore the extensions. For example:
SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ...
If you add a version number after the '!', the syntax will only
be executed if the MySQL version is equal to or newer than the used version
number:
CREATE /*!32302 TEMPORARY */ TABLE (a int);
The above means that if you have Version 3.23.02 or newer, then MySQL will
use the TEMPORARY keyword.
MySQL extensions are listed below:
MEDIUMINT, SET,
ENUM, and the different BLOB and TEXT
types.
AUTO_INCREMENT, BINARY,
NULL, UNSIGNED, and ZEROFILL.
BINARY
attribute or use the BINARY cast, which causes comparisons to be
done according to the ASCII order used on the MySQL server host.
db_name.tbl_name syntax. Some SQL servers provide the same
functionality but call this User space. MySQL doesn't support
tablespaces as in: create table ralph.my_table...IN
my_tablespace.
LIKE is allowed on numeric columns.
INTO OUTFILE and STRAIGHT_JOIN in a
SELECT statement. See section 6.4.1
SELECT Syntax.
SQL_SMALL_RESULT option in a SELECT
statement.
EXPLAIN SELECT to get a description on how tables are joined.
INDEX or KEY in a CREATE TABLE
statement. See section 6.5.3
CREATE TABLE Syntax.
TEMPORARY or IF NOT EXISTS with
CREATE TABLE.
COUNT(DISTINCT list) where 'list' is more than one
element.
CHANGE col_name, DROP col_name, or
DROP INDEX, IGNORE or RENAME in an
ALTER TABLE statement. See section 6.5.4
ALTER TABLE Syntax.
RENAME TABLE. See section 6.5.5
RENAME TABLE Syntax.
ADD, ALTER, DROP,
or CHANGE clauses in an ALTER TABLE statement.
DROP TABLE with the keywords IF EXISTS.
DROP TABLE
statement.
LIMIT clause of the DELETE statement.
DELAYED clause of the INSERT and
REPLACE statements.
LOW_PRIORITY clause of the INSERT,
REPLACE, DELETE, and UPDATE statements.
LOAD DATA INFILE. In many cases, this syntax is
compatible with Oracle's LOAD DATA INFILE. See section 6.4.9
LOAD DATA INFILE Syntax.
ANALYZE TABLE, CHECK TABLE, OPTIMIZE
TABLE, and REPAIR TABLE statements.
SHOW statement. See section 4.5.6
SHOW Syntax.
SET OPTION statement. See section 5.5.6
SET Syntax.
GROUP BY
part. This gives better performance for some very specific, but quite normal
queries. See section 6.3.6
Functions for Use with GROUP BY Clauses.
ASC and DESC with GROUP
BY.
|| and &&
operators to mean logical OR and AND, as in the C programming language. In
MySQL, || and OR are synonyms, as are
&& and AND. Because of this nice syntax,
MySQL doesn't support the ANSI SQL || operator for string
concatenation; use CONCAT() instead. Because
CONCAT() takes any number of arguments, it's easy to convert use
of the || operator to MySQL.
CREATE DATABASE or DROP DATABASE. See section 6.5.1
CREATE DATABASE Syntax.
% operator is a synonym for MOD(). That is,
N % M is equivalent to MOD(N,M). % is
supported for C programmers and for compatibility with PostgreSQL.
=, <>, <=
,<, >=,>,
<<, >>, <=>,
AND, OR, or LIKE operators may be used
in column comparisons to the left of the FROM in
SELECT statements. For example: mysql> SELECT col1=1 AND col2=2 FROM tbl_name;
LAST_INSERT_ID() function. See section 8.4.3.126
mysql_insert_id().
REGEXP and NOT REGEXP extended regular
expression operators.
CONCAT() or CHAR() with one argument or more
than two arguments. (In MySQL, these functions can take any number of
arguments.)
BIT_COUNT(), CASE, ELT(),
FROM_DAYS(), FORMAT(), IF(),
PASSWORD(), ENCRYPT(), MD5(),
ENCODE(), DECODE(), PERIOD_ADD(),
PERIOD_DIFF(), TO_DAYS(), or WEEKDAY()
functions.
TRIM() to trim substrings. ANSI SQL only supports
removal of single characters.
GROUP BY functions STD(),
BIT_OR(), and BIT_AND().
REPLACE instead of DELETE +
INSERT. See section 6.4.8
REPLACE Syntax.
FLUSH, RESET and DO statements.
:=: SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg FROM test_table; SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;
We try to make MySQL follow the ANSI SQL standard and the ODBC SQL standard, but in some cases MySQL does things differently:
VARCHAR columns, trailing spaces are removed when the
value is stored. See section 1.7.5 Known
Errors and Design Deficiencies in MySQL.
CHAR columns are silently changed to
VARCHAR columns. See section 6.5.3.1
Silent Column Specification Changes.
REVOKE to revoke privileges
for a table. See section 4.3.1
GRANT and REVOKE Syntax.
NULL AND FALSE will evaluate to NULL and not to
FALSE. This is because we don't think it's good to have to
evaluate a lot of extra conditions in this case. For a prioritised list indicating when new extensions will be added to MySQL, you should consult the online MySQL TODO list at http://www.mysql.com/documentation/manual.php?section=TODO. That is the latest version of the TODO list in this manual. See section 1.8 MySQL and The Future (The TODO).
SELECTsMySQL currently only supports nested queries of the form INSERT ...
SELECT ... and REPLACE ... SELECT .... You can however use
the function IN() in other contexts. Sub-selects are scheduled for
implementation in Version 4.x.
Meanwhile, you can often rewrite the query without a sub-select:
SELECT * FROM table1 WHERE id IN (SELECT id FROM table2);
This can be re-written as:
SELECT table1.* FROM table1,table2 WHERE table1.id=table2.id;
The queries:
SELECT * FROM table1 WHERE id NOT IN (SELECT id FROM table2);
SELECT * FROM table1 WHERE NOT EXISTS (SELECT id FROM table2
WHERE table1.id=table2.id);
Can be rewritten as:
SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.id=table2.id
WHERE table2.id IS NULL;
For more complicated subqueries you can often create temporary tables to hold
the subquery. In some cases, however this option will not work. The most
frequently encountered of these cases arises with DELETE
statements, for which standard SQL does not support joins (except in
sub-selects). For this situation there are two options available until
subqueries are supported by MySQL.
The first option is to use a procedural programming language (such as Perl or
PHP) to submit a SELECT query to obtain the primary keys for the
records to be deleted, and then use these values to construct the
DELETE statement (DELETE FROM ... WHERE ... IN (key1, key2,
...)).
The second option is to use interactive SQL to contruct a set of
DELETE statements automatically, using the MySQL extension
CONCAT() (in lieu of the standard || operator). For
example:
SELECT CONCAT('DELETE FROM tab1 WHERE pkid = ', tab1.pkid, ';')
FROM tab1, tab2
WHERE tab1.col1 = tab2.col2;
You can place this query in a script file and redirect input from it to the
mysql command-line interpreter, piping its output back to a second
instance of the interpreter:
shell> mysql --skip-column-names mydb < myscript.sql | mysql mydb
MySQL 4.0 supports multi-table deletes that can be used to efficiently delete rows based on information from one table or even from many tables at the same time.
SELECT INTO TABLEMySQL doesn't yet support the Oracle SQL extension: SELECT ... INTO
TABLE .... MySQL supports instead the ANSI SQL syntax INSERT INTO
... SELECT ..., which is basically the same thing. See section 6.4.3.1
INSERT ... SELECT Syntax.
INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID
FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;
Alternatively, you can use SELECT INTO OUTFILE... or
CREATE TABLE ... SELECT.
MySQL supports transactions with the InnoDB and BDB
Transactional table handlers. See section 7 MySQL
Table Types. InnoDB provides ACID compliancy.
However, the non-transactional table types in MySQL such as
MyISAM follow another paradigm for data integrity called
``Atomic Operations.'' Atomic operations often offer equal or even
better integrity with much better performance. With MySQL supporting both
paradigms, the user is able to decide if they need the speed of atomic
operations or if they need to use transactional features in their applications.
This choice can be made on a per-table basis.
How does one use the features of MySQL to maintain rigorous integrity and how do these features compare with the transactional paradigm?
ROLLBACK instead of
COMMIT in critical situations, then transactions are more
convenient. Transactions also ensure that unfinished updates or corrupting
activities are not committed to the database; the server is given the
opportunity to do an automatic rollback and your database is saved. MySQL, in
almost all cases, allows you to resolve potential problems by including simple
checks before updates and by running simple scripts that check the databases
for inconsistencies and automatically repair or warn if such an inconsistency
occurs. Note that just by using the MySQL log or even adding one extra log,
one can normally fix tables perfectly with no data integrity loss.
LOCK TABLES or atomic updates, ensuring that you
never will get an automatic abort from the database, which is a common problem
with transactional databases.
The transactional paradigm has its benefits and its drawbacks. Many users and application developers depend on the ease with which they can code around problems where an abort appears to be, or is necessary. However, even if you are new to the atomic operations paradigm, or more familiar with transactions, do consider the speed benefit that non-transactional tables can offer, on the order of three to five times the speed of the fastest and most optimally tuned transactional tables.
In situations where integrity is of highest importance, MySQL offers
transaction-level or better reliability and integrity even for non-transactional
tables. If you lock tables with LOCK TABLES, all updates will stall
until any integrity checks are made. If you only obtain a read lock (as opposed
to a write lock), then reads and inserts are still allowed to happen. The new
inserted records will not be seen by any of the clients that have a
READ lock until they release their read locks. With INSERT
DELAYED you can queue inserts into a local queue, until the locks are
released, without having the client wait for the insert to complete. See section
6.4.4
INSERT DELAYED Syntax.
``Atomic,'' in the sense that we mean it, is nothing magical. It only means that you can be sure that while each specific update is running, no other user can interfere with it, and there will never be an automatic rollback (which can happen with transactional tables if you are not very careful). MySQL also guarantees that there will not be any dirty reads.
Following are some techniques for working with non-transactional tables:
LOCK TABLES, and you don't need cursors when you can update
records on the fly.
ROLLBACK, you can use the following strategy:
LOCK TABLES ... to lock all the tables you want to
access.
UNLOCK TABLES to release your locks. ROLLBACKs, although not always. The only situation this solution
doesn't handle is when someone kills the threads in the middle of an update.
In this case, all locks will be released but some of the updates may not have
been executed.
WHERE
clause in the UPDATE statement. If the record wasn't updated, we
give the client a message: "Some of the data you have changed have been
changed by another user". Then we show the old row versus the new row in a
window, so the user can decide which version of the customer record he should
use. This gives us something that is similar to column locking but is actually
even better, because we only update some of the columns, using values that are
relative to their current values. This means that typical UPDATE
statements look something like these: UPDATE tablename SET pay_back=pay_back+'relative change';
UPDATE customer
SET
customer_date='current_date',
address='new address',
phone='new phone',
money_he_owes_us=money_he_owes_us+'new_money'
WHERE
customer_id=id AND address='old address' AND phone='old phone';
As you can see, this is very efficient and works even if another client
has changed the values in the pay_back or
money_he_owes_us columns.
ROLLBACK and/or LOCK TABLES for the purpose of
managing unique identifiers for some tables. This can be handled much more
efficiently by using an AUTO_INCREMENT column and either the SQL
function LAST_INSERT_ID() or the C API function
mysql_insert_id(). See section 8.4.3.126
mysql_insert_id(). Generally, you can code around row-level locking. Some cases
really need it, but they are very few. For instance, you can use a flag column
in the table and do something like this: UPDATE tbl_name SET row_flag=1 WHERE id=ID;MySQL returns 1 for the number of affected rows if the row was found and
row_flag wasn't already 1 in the original row. You can think of
it as MySQL changed the above query to: UPDATE tbl_name SET row_flag=1 WHERE id=ID and row_flag <> 1;
A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep reissuing the entire query but can refer to the stored procedure. This provides better performance because the query has to be parsed only once, and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server.
A trigger is a stored procedure that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that automatically deletes the corresponding customer from a customer table when all his transactions are deleted.
The planned update language will be able to handle stored procedures. Our aim is to have stored procedures implemented in MySQL 4.1. We are also looking at triggers.
Note that foreign keys in SQL are not used to join tables, but are used
mostly for checking referential integrity (foreign key constraints). If you want
to get results from multiple tables from a SELECT statement, you do
this by joining tables:
SELECT * from table1,table2 where table1.id = table2.id;
See section 6.4.1.1
JOIN Syntax. See section 3.5.6
Using Foreign Keys.
In MySQL 3.23.44 and up, InnoDB tables supports checking of
foreign key constraints. See section 7.5 InnoDB
Tables. For other table types, MySQL does parse the FOREIGN KEY
syntax in CREATE TABLE commands, but without further action being
taken.
The FOREIGN KEY syntax without ON DELETE ... is
mostly used for documentation purposes. Some ODBC applications may use this to
produce automatic WHERE clauses, but this is usually easy to
override. FOREIGN KEY is sometimes used as a constraint check, but
this check is unnecessary in practice if rows are inserted into the tables in
the right order.
In MySQL, you can work around the problem of ON DELETE ... not
being implemented by adding the appropriate DELETE statement to an
application when you delete records from a table that has a foreign key. In
practice this is as quick (in some cases quicker) and much more portable than
using foreign keys.
In MySQL 4.0 you can use multi-table delete to delete rows from many tables
with one command. See section 6.4.6
DELETE Syntax.
In the near future we will extend the FOREIGN KEY implementation
so that the information will be saved in the table specification file and may be
retrieved by mysqldump and ODBC. At a later stage we will implement
the foreign key constraints for applications that can't easily be coded to avoid
them.
Do keep in mind that foreign keys are often misused, which can cause severe problems. Even when used properly, it is not a magic solution for the referential integrity problem, although it does make things easier in some cases.
Some advantages of foreign key enforcement:
Disadvantages:
It is planned to implement views in MySQL around Version 4.1.
Views are mostly useful for letting users access a set of relations as one table (in read-only mode). Many SQL databases don't allow one to update any rows in a view, but you have to do the updates in the separate tables.
As MySQL is mostly used in applications and on web system where the application writer has full control on the database usage, most of our users haven't regarded views to be very important. (At least no one has been interested enough in this to be prepared to finance the implementation of views).
One doesn't need views in MySQL to restrict access to columns as MySQL has a very sophisticated privilege system. See section 4.2 General Security Issues and the MySQL Access Privilege System.
Some other SQL databases use `--' to start comments. MySQL has
`#' as the start comment character. You can also use the C comment
style /* this is a comment */ with MySQL. See section 6.1.5
Comment Syntax.
MySQL Version 3.23.3 and above supports the `--' comment style,
provided the comment is followed by a space. This is because this comment style
has caused many problems with automatically generated SQL queries that have used
something like the following code, where we automatically insert the value of
the payment for !payment!:
UPDATE tbl_name SET credit=credit-!payment!
Think about what happens if the value of payment is negative?
Because 1--1 is legal in SQL, the consequences of allowing comments
to start with `--' are terrible.
Using our implementation of this method of commenting in MySQL Version 3.23.3
and up, 1-- This is a comment is actually safe.
Another safe feature is that the mysql command-line client
removes all lines that start with `--'.
The following information is only relevant if you are running a MySQL version earlier than Version 3.23.3:
If you have a SQL program in a text file that contains `--' comments you should use:
shell> replace " --" " #" < text-file-with-funny-comments.sql \
| mysql database
instead of the usual:
shell> mysql database < text-file-with-funny-comments.sql
You can also edit the command file ``in place'' to change the `--' comments to `#' comments:
shell> replace " --" " #" -- text-file-with-funny-comments.sql
Change them back with this command:
shell> replace " #" " --" -- text-file-with-funny-comments.sql
The following problems are known and have a very high priority to get fixed:
ANALYZE TABLE on a BDB table may in some case make the table
unusable until one has restarted mysqld. When this happens you
will see errors like the following in the MySQL error file: 001207 22:07:56 bdb: log_flush: LSN past current end-of-log
ALTER TABLE on a BDB table on
which you are running not completed multi-statement transactions. (The
transaction will probably be ignored).
ANALYZE TABLE, OPTIMIZE TABLE and REPAIR
TABLE may cause problems on tables for which you are using INSERT
DELAYED.
LOCK TABLE .. and FLUSH TABLES ..
doesn't guarantee that there isn't a half-finished transaction in progress on
the table.
mysql client on the
database if you are not using the -A option or if you are using
rehash. This is especially notable when you have a big table
cache.
LOAD DATA
INFILE and line terminator characters of more than 1 character.
The following problems are known and will be fixed in due time:
SET CHARACTER SET, one can't use translated
characters in database, table and column names.
DELETE FROM merge_table used without a WHERE
will only clear the mapping for the table, not delete everything in the mapped
tables.
BLOB values can't ``reliably'' be used in GROUP
BY or ORDER BY or DISTINCT. Only the first
max_sort_length bytes (default 1024) are used when comparing
BLOBbs in these cases. This can be changed with the -O
max_sort_length option to mysqld. A workaround for most
cases is to use a substring: SELECT DISTINCT LEFT(blob,2048) FROM
tbl_name.
BIGINT or DOUBLE (both
are normally 64 bits long). It depends on the function which precision one
gets. The general rule is that bit functions are done with BIGINT
precision, IF, and ELT() with BIGINT or
DOUBLE precision and the rest with DOUBLE precision.
One should try to avoid using bigger unsigned long long values than 63 bits
(9223372036854775807) for anything else than bit fields! MySQL 4.0 has better
BIGINT handling than 3.23.
BLOB and TEXT
columns, automatically have all trailing spaces removed when retrieved. For
CHAR types this is okay, and may be regarded as a feature
according to ANSI SQL92. The bug is that in MySQL, VARCHAR
columns are treated the same way.
ENUM and SET columns
in one table.
safe_mysqld re-directs all messages from mysqld
to the mysqld log. One problem with this is that if you execute
mysqladmin refresh to close and reopen the log,
stdout and stderr are still redirected to the old
log. If you use --log extensively, you should edit
safe_mysqld to log to `'hostname'.err' instead of
`'hostname'.log' so you can easily reclaim the space for the old log
by deleting the old one and executing mysqladmin refresh.
UPDATE statement, columns are updated from left to
right. If you refer to an updated column, you will get the updated value
instead of the original value. For example: mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1;This will update
KEY with 2 instead of with
1.
select * from temporary_table, temporary_table as t2;
RENAME doesn't work with TEMPORARY tables or
tables used in a MERGE table.
DISTINCT differently if you are
using 'hidden' columns in a join or not. In a join, hidden columns are counted
as part of the result (even if they are not shown) while in normal queries
hidden columns doesn't participate in the DISTINCT comparison. We
will probably change this in the future to never compare the hidden columns
when executing DISTINCT An example of this is: SELECT DISTINCT mp3id FROM band_downloads
WHERE userid = 9 ORDER BY id DESC;
and SELECT DISTINCT band_downloads.mp3id
FROM band_downloads,band_mp3
WHERE band_downloads.userid = 9
AND band_mp3.id = band_downloads.mp3id
ORDER BY band_downloads.id DESC;
In the second case you may in MySQL 3.23.x get two identical rows in the
result set (because the hidden 'id' column may differ). Note that the this
only happens for queries where you don't have the ORDER BY columns in the
result, something that is you are not allowed to do in ANSI SQL.
rollback data, some things behave a
little differently in MySQL than in other SQL servers. This is just to ensure
that MySQL never need to do a rollback for a SQL command. This may be a little
awkward at times as column values must be checked in the application, but this
will actually give you a nice speed increase as it allows MySQL to do some
optimisations that otherwise would be very hard to do. If you set a column to
an incorrect value, MySQL will, instead of doing a rollback, store the
best possible value in the column:
NULL into a column that doesn't take
NULL values, MySQL will store 0 or '' (empty
string) in it instead. (This behavior can, however, be changed with the
-DDONT_USE_DEFAULT_FIELDS compile option).
DATE
and DATETIME columns. (Like 2000-02-31 or 2000-02-00). If the
date is totally wrong, MySQL will store the special 0000-00-00 date value in
the column.
ENUM column to an unsupported value, it will
be set to the error value 'empty string', with numeric value 0.
SET column to an unsupported value, the value
will be ignored. PROCEDURE on a query that returns an empty
set, in some cases the PROCEDURE will not transform the columns.
MERGE doesn't check if the
underlying tables are of compatible types.
NaN, -Inf and
Inf values in double. Using these will cause problems when trying
to export and import data. We should as an intermediate solution change
NaN to NULL (if possible) and -Inf and
Inf to the Minimum respective maximum possible
double value.
LIMIT on negative numbers are treated as big positive
numbers.
ALTER TABLE to first add an UNIQUE
index to a table used in a MERGE table and then use ALTER
TABLE to add a normal index on the MERGE table, the key
order will be different for the tables if there was an old not-unique key in
the table. This is because ALTER TABLE puts UNIQUE
keys before normal keys to be able to detect duplicate keys as early as
possible. The following are known bugs in earlier versions of MySQL:
DROP TABLE on a table
that is one among many tables that is locked with LOCK TABLES.
LOCK table with WRITE
FLUSH TABLES UPDATE that updated a key with
a WHERE on the same key may have failed because the key was used
to search for records and the same row may have been found multiple times: UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;A workaround is to use:
mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;This will work because MySQL will not use index on expressions in the
WHERE clause.
For platform-specific bugs, see the sections about compiling and porting.
This appendix lists the features that we plan to implement in MySQL.
Everything in this list is approximately in the order it will be done. If you want to affect the priority order, please register a license or support us and tell us what you want to have done more quickly. See section 1.4 MySQL Support and Licensing.
The plan is that we in the future will support the full ANSI SQL99 standard, but with a lot of useful extensions. The challenge is to do this without sacrifying the speed or compromise the code.
We have now shifted development to MySQL Version 4.0. Most of the basic things we want to have in 4.0 are already done. The target is to quickly implement the rest of the following features and then shift development to MySQL 4.1. See section 1.5 MySQL 4.0 In A Nutshell.
The news section for 4.0 includes a list of the features we have already implemented in the 4.0 tree. See section D.1 Changes in release 4.0.x (Development; Alpha).
This section lists features not yet implemented in the current version of MySQL 4.0, which will however be implemented in later versions of MySQL 4.0. This being very volatile information, please consider this list valid only if you are reading it from the MySQL web site (http://mysql.com/).
.frm files) This will
enable us to not run out of bits when adding more table options. One will
still be able to use the old .frm file format with 4.0. All newly
created tables will, however, use the new format. The new file format will
enable us to add new column types, more options for keys and FOREIGN
KEY support.
RAND() and user variables
@var.
DELETE on MyISAM tables to use the record
cache. To do this, we need to update the threads record cache when we update
the .MYD file.
SHOW COLUMNS FROM table_name (used by mysql
client to allow expansions of column names) should not open the table, but
only the definition file. This will require less memory and be much faster.
SET CHARACTER SET we should translate the whole
query at once and not only strings. This will enable users to use the
translated characters in database, table and column names.
gethostbyaddr_r() so that we
can change ip_to_hostname() to not block other threads while
doing DNS lookups.
record_in_range() method to MERGE tables to
be able to choose the right index when there is many to choose from. We should
also extend the info interface to get the key distribution for each index, of
analyze is run on all sub tables.
RENAME TABLE on a table used in an active MERGE
table may corrupt the table.
SET SQL_DEFAULT_TABLE_TYPE=[MyISAM | INNODB | BDB | HEAP].
select id from t where grp in (select grp from g where u
> 100)
update items,month set
items.price=month.price where items.id=month.id;;
SELECT a.col1, b.col2
FROM (SELECT MAX(col1) AS col1 FROM root_table) a,
other_table b
WHERE a.col1=b.col1;
This could be done by automatically creating temporary tables for the
derived tables for the duration of the query.
PREPARE of statements and sending of parameters to
mysqld.
INSERT ... SELECT to optionally use concurrent
inserts.
RENAME DATABASE. To make this safe for all table
handlers, it should work as follows:
RENAME command.
SELECT MIN(column) ...
GROUP BY.
PREPARE of statements and sending of parameters to
mysqld.
long_query_time with a
granularity in microseconds.
mysql command line client,
with options like database in use, time and date...
myisampack code into the server.
INSERT/DELETE/UPDATE
so that we can gracefully recover if the index file gets full.
ALTER TABLE on a table that is symlinked to
another disk, create temporary tables on this disk.
DATE/DATETIME type that handles time zone
information properly, so that dealing with dates in different time zones is
easier.
MyISAM) without threads.
INSERT SQL_CONCURRENT and mysqld
--concurrent-insert to do a concurrent insert at the end of the file if
the file is read-locked.
FOREIGN key definitions in the `.frm' file.
DELETE
lockd works with modern Linux kernels; If not, we
have to fix lockd! To test this, start mysqld with
--enable-locking and run the different fork* test suits. They
shouldn't give any errors if lockd works.
LIMIT, like in LIMIT
@a,@b.
UPDATE statements. For example:
UPDATE TABLE foo SET @a=a+b,a=@a, b=@a+c
GROUP BY, as in the following example: SELECT id,
@a:=count(*), sum(sum_col)/@a FROM table_name GROUP BY id.
DEFAULT values to columns. Give an error
when using an INSERT that doesn't contain a column that doesn't
have a DEFAULT.
SELECT
CACHED ...
mysql_query() commands
in a row without reading results or give a nice error message when one does
this.
BIT type to take 1 bit (now BIT takes 1
char).
ctime() doesn't work on some FreeBSD
systems.
IMAGE option to LOAD DATA INFILE to not
update TIMESTAMP and AUTO_INCREMENT fields.
LOAD DATE INFILE.. UPDATE syntax.
LOAD DATA INFILE ... REPLACE INTO is now. LOAD DATA INFILE understand syntax like: LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name
TEXT_FIELDS (text_field1, text_field2, text_field3)
SET table_field1=concatenate(text_field1, text_field2),
table_field3=23
IGNORE text_field3
This can be used to skip over extra columns in the text file, or update
columns based on expressions of the read data...
LOAD DATA INFILE 'file_name' INTO TABLE 'table_name' ERRORS TO
err_table_name This would cause any errors and warnings to be logged
into the err_table_name table. That table would have a structure
like: line_number - line number in data file error_message - the error/warning message and maybe data_line - the line from the data file
VARCHAR support (There is already support for this
in MyISAM).
mysql to Netscape.
LOCK DATABASES. (with various options)
DECIMAL and NUMERIC types can't read exponential
numbers; Field_decimal::store(const char *from,uint len) must be
recoded to fix this.
t1 JOIN t2 ON ... and t1 JOIN t2 USING
... Currently, you can only use this syntax with LEFT
JOIN.
unsigned long long type.
show status. Counts for:
INSERT/DELETE/UPDATE statements.
Records reads and updated. Selects on 1 table and selects with joins. Mean
number of tables in select. Number of ORDER BY and GROUP
BY queries.
mysql in the middle of a query, you should open
another connection and kill the old running query. Alternatively, an attempt
should be made to detect this in the server.
SHOW INFO FROM tbl_name for basic
table information should be implemented.
NATURAL JOIN and UNION JOIN
select a from crash_me left join crash_me2 using (a);
In this case a is assumed to come from the crash_me
table.
ON and USING works with the
JOIN join type.
CONNECT BY PRIOR ... to search hierarchy
structures.
mysqladmin copy database new-database; Requires
COPY command to be added to mysqld
SHOW HOSTS for printing information about the hostname cache.
DELETE and REPLACE options to the
UPDATE statement (this will delete rows when one gets a duplicate
key error while updating).
DATETIME to store fractions of seconds.
NULL for calculated
columns.
SELECT
COUNT(*)*(id+0) FROM table_name GROUP BY id
ALTER TABLE doesn't abort clients that executes
INSERT DELAYED.
UPDATE clause contains
the old values before the update started.
myisamchk, REPAIR and OPTIMIZE
TABLE should be able to handle cases where the data and/or index files
are symbolic links.
pread()/pwrite() on Windows to
enable concurrent inserts.
SUM(DISTINCT)
ANY(),EVERY() and SOME() group
functions. In ANSI SQL these only works on boolean columns, but we can extend
these to work on any columns/expressions by applying: value == 0 -> FALSE
and value <> 0 -> TRUE.
MAX(column) is the same as the column
type. create table t1 (a DATE); insert into t1 values (now()); create table t2 select MAX(a) from t1; show columns from t2;
UPDATE
the row if it exists and INSERT a new row if the row didn't
exist. (Like REPLACE works with INSERT /
DELETE) get_changed_tables(timeout,table1,table2,...)
SHOW
commands.
SET TIMESTAMP=#;
MINUS, INTERSECT and FULL OUTER
JOIN. (Currently UNION (in 4.0) and LEFT OUTER
JOIN are supported)
UNIQUE on fields that can be NULL.
SQL_OPTION MAX_SELECT_TIME=# to put a time limit on a query.
LIMIT to retrieve data from the end.
safe_mysqld: according to FSSTND
(which Debian tries to follow) PID files should go into
`/var/run/<progname>.pid' and log files into
`/var/log'. It would be nice if you could put the "DATADIR" in the
first declaration of "pidfile" and "log", so the placement of these files can
be changed with a single statement.
zlib() for gzip-ed files to
LOAD DATA INFILE.
BLOB columns (partly solved now).
AUTO_INCREMENT value when one sets a
column to 0. Use NULL instead.
JOIN with parentheses.
GET_LOCK. When doing
this, one must also handle the possible deadlocks this change will introduce.
Time is given according to amount of work, not real time.
Our users have successfully run their own benchmarks against a number of
Open Source and traditional database servers. We are aware of tests
against Oracle, DB/2, Microsoft SQL
Server and other commercial products. Due to legal reasons we are
restricted from publishing some of those benchmarks in our reference manual.
This section includes a comparison with mSQL for historical
reasons and with PostgreSQL as it is also an Open Source database.
If you have benchmark results that we can publish, please contact us at benchmarks@mysql.com.
For comparative lists of all supported functions and types as well as
measured operational limits of many different database systems, see the
crash-me web page at http://www.mysql.com/information/crash-me.php.
mSQLmSQL should be
quicker at:
INSERT operations into very simple tables with few columns
and keys.
CREATE TABLE and DROP TABLE.
SELECT on something that isn't an index. (A table scan is
very easy.) mSQL (and most other SQL implementations) on the
following:
SELECT operations.
VARCHAR columns.
SELECT with many expressions.
SELECT on large tables.
mSQL, once one connection is
established, all others must wait until the first has finished, regardless
of whether the connection is running a query that is short or long. When the
first connection terminates, the next can be served, while all the others
wait again, etc.
mSQL can become pathologically slow if you change
the order of tables in a SELECT. In the benchmark suite, a time
more than 15000 times slower than MySQL was seen. This is due to
mSQL's lack of a join optimiser to order tables in the optimal
order. However, if you put the tables in exactly the right order in
mSQL2 and the WHERE is simple and uses index
columns, the join will be relatively fast! See section 5.1.4
The MySQL Benchmark Suite.
ORDER BY and GROUP BY.
DISTINCT.
TEXT or BLOB columns. GROUP BY and HAVING. mSQL does
not support GROUP BY at all. MySQL supports a full GROUP
BY with both HAVING and the following functions:
COUNT(), AVG(), MIN(),
MAX(), SUM(), and STD().
COUNT(*) is optimised to return very quickly if the
SELECT retrieves from one table, no other columns are
retrieved, and there is no WHERE clause. MIN() and
MAX() may take string arguments.
INSERT and UPDATE with calculations. MySQL can
do calculations in an INSERT or UPDATE. For
example: mysql> UPDATE SET x=x*10+y WHERE x<20;
SELECT with functions. MySQL has many functions (too many
to list here; see section 6.3
Functions for Use in SELECT and WHERE
Clauses). MEDIUMINT that is 3 bytes long. If you have
100,000,000 records, saving even one byte per record is very important.
mSQL2 has a more limited set of column types, so it is more
difficult to get small tables.
mSQL
stability, so we cannot say anything about that.
mSQL, and is also less expensive than mSQL.
Whichever product you choose to use, remember to at least consider paying for
a license or e-mail support.
mSQL with
some added features.
mSQL has a
JDBC driver, but we have too little experience with it to compare.
GROUP BY, and
so on are still not implemented in mSQL, it has a lot of catching
up to do. To get some perspective on this, you can view the mSQL
`HISTORY' file for the last year and compare it with the News section
of the MySQL Reference Manual (see section D MySQL
change history). It should be pretty obvious which one has developed most
rapidly.
mSQL and MySQL have many interesting third-party tools.
Because it is very easy to port upward (from mSQL to MySQL),
almost all the interesting applications that are available for
mSQL are also available for MySQL. MySQL comes with a simple
msql2mysql program that fixes differences in spelling between
mSQL and MySQL for the most-used C API functions. For example, it
changes instances of msqlConnect() to
mysql_connect(). Converting a client program from
mSQL to MySQL usually requires only minor effort. mSQL Tools for
MySQLAccording to our experience, it doesn't take long to convert tools such as
msql-tcl and msqljava that use the mSQL C
API so that they work with the MySQL C API.
The conversion procedure is:
msql2mysql on the source. This requires
the replace program, which is distributed with MySQL.
Differences between the mSQL C API and the MySQL C API are:
MYSQL structure as a connection type
(mSQL uses an int).
mysql_connect() takes a pointer to a MYSQL
structure as a parameter. It is easy to define one globally or to use
malloc() to get one. mysql_connect() also takes two
parameters for specifying the user and password. You may set these to
NULL, NULL for default use.
mysql_error() takes the MYSQL structure as a
parameter. Just add the parameter to your old msql_error() code
if you are porting old code.
mSQL returns only a text error message.
mSQL and MySQL Client/Server
Communications Protocols DifferThere are enough differences that it is impossible (or at least not easy) to support both.
The most significant ways in which the MySQL protocol differs from the
mSQL protocol are listed below:
mSQL 2.0 SQL Syntax Differs
from MySQLColumn types
MySQL
CREATE TABLE Syntax):
ENUM type for one of a set of strings.
SET type for many of a set of strings.
BIGINT type for 64-bit integers. UNSIGNED option for integer columns.
ZEROFILL option for integer columns.
AUTO_INCREMENT option for integer columns that are a
PRIMARY KEY. See section 8.4.3.126
mysql_insert_id().
DEFAULT value for all columns. mSQL2
mSQL column types correspond to the MySQL types shown below:
mSQL type |
Corresponding MySQL type |
CHAR(len) |
CHAR(len) |
TEXT(len) |
TEXT(len). len is the maximal length. And
LIKE works. |
INT |
INT. With many more options! |
REAL |
REAL. Or FLOAT. Both 4- and 8-byte
versions are available. |
UINT |
INT UNSIGNED |
DATE |
DATE. Uses ANSI SQL format rather than
mSQL's own format. |
TIME |
TIME |
MONEY |
DECIMAL(12,2). A fixed-point value with two decimals.
|
Index Creation
MySQL
CREATE
TABLE statement.
mSQL
CREATE INDEX statements. To Insert a Unique Identifier into a Table
MySQL
AUTO_INCREMENT as a column type specifier. See section 8.4.3.126
mysql_insert_id().
mSQL
SEQUENCE on a table and select the _seq
column. To Obtain a Unique Identifier for a Row
MySQL
PRIMARY KEY or UNIQUE key to the table and
use this. New in Version 3.23.11: If the PRIMARY or
UNIQUE key consists of only one column and this is of type
integer, one can also refer to it as _rowid.
mSQL
_rowid column. Observe that _rowid may
change over time depending on many factors. To Get the Time a Column Was Last Modified
MySQL
TIMESTAMP column to the table. This column is
automatically set to the current date and time for INSERT or
UPDATE statements if you don't give the column a value or if you
give it a NULL value.
mSQL
_timestamp column. NULL Value Comparisons
MySQL
NULL is always
NULL.
mSQL
mSQL, NULL = NULL is TRUE. You must change
=NULL to IS NULL and <>NULL to
IS NOT NULL when porting old code from mSQL to
MySQL. String Comparisons
MySQL
BINARY attribute, which causes comparisons to be done according
to the ASCII order used on the MySQL server host.
mSQL
Case-insensitive Searching
MySQL
LIKE is a case-insensitive or case-sensitive operator,
depending on the columns involved. If possible, MySQL uses indexes if the
LIKE argument doesn't start with a wild-card character.
mSQL
CLIKE. Handling of Trailing Spaces
MySQL
CHAR and VARCHAR
columns. Use a TEXT column if this behavior is not desired.
mSQL
WHERE Clauses
MySQL
AND is evaluated
before OR). To get mSQL behavior in MySQL, use
parentheses (as shown in an example below).
mSQL
mSQL
query: mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4;To make MySQL evaluate this the way that
mSQL would, you
must add parentheses: mysql> SELECT * FROM table WHERE (a=1 AND (b=2 OR (a=3 AND (b=4))));
Access Control
MySQL
mSQL
PostgreSQLWhen reading the following, please note that both products are continually evolving. We at MySQL AB and the PostgreSQL developers are both working on making our respective database as good as possible, so we are both a serious alternative to any commercial database.
The following comparison is made by us at MySQL AB. We have tried to be as accurate and fair as possible, but because while we know MySQL througly we don't have a full knowledge of all PostgreSQL features, so we may have got some things wrong. We will however correct these when they come to our attention.
We would first like to note that PostgreSQL and MySQL are both widely used
products, but with different design goals, even if we are both striving towards
ANSI SQL compliancy. This means that for some applications MySQL is more suited,
while for others PostgreSQL is more suited. When choosing which database to use,
you should first check if the database's feature set satisfies your application.
If you need raw speed, MySQL is probably your best choice. If you need some of
the extra features that only PostgreSQL can offer, you should use
PostgreSQL.
When adding things to MySQL we take pride to do an optimal, definite solution. The code should be so good that we shouldn't have any need to change it in the foreseeable future. We also do not like to sacrifice speed for features but instead will do our utmost to find a solution that will give maximal throughput. This means that development will take a little longer, but the end result will be well worth this. This kind of development is only possible because all server code are checked by one of a few (currently two) persons before it's included in the MySQL server.
We at MySQL AB believe in frequent releases to be able to push out new features quickly to our users. Because of this we do a new small release about every three weeks, and a major branch every year. All releases are throughly tested with our testing tools on a lot of different platforms.
PostgreSQL is based on a kernel with lots of contributors. In this setup it makes sense to prioritise adding a lot of new features, instead of implementing them optimally, because one can always optimise things later if there arises a need for this.
Another big difference between MySQL and PostgreSQL is that nearly all of the code in the MySQL server are coded by developers that are employed by MySQL AB and are still working on the server code. The exceptions are the transaction engines, and the regexp library.
This is in sharp contrast to the PostgreSQL code where the majority of the code is coded by a big group of people with different backgrounds. It was only recently that the PostgreSQL developers announced that their current developer group had finally had time to take a look at all the code in the current PostgreSQL release.
Both of the above development methods have their own merits and drawbacks. We here at MySQL AB think of course that our model is better because our model gives better code consistency, more optimal and reusable code, and in our opinion, fewer bugs. Because we are the authors of the MySQL server code, we are better able to coordinate new features and releases.
On the crash-me page (http://www.mysql.com/information/crash-me.php) you can find a list of those database constructs and limits that one can detect automatically with a program. Note however that a lot of the numerical limits may be changed with startup options for respective database. The above web page is however extremely useful when you want to ensure that your applications works with many different databases or when you want to convert your application from one database to another.
MySQL offers the following advantages over PostgreSQL:
MySQL is generally much faster than PostgreSQL.
Cygwin emulation. We have heard that PostgreSQL is not
yet that stable on Windows but we haven't been able to verify this ourselves.
VACUUM() once in a while to reclaim space
from UPDATE and DELETE commands and to perform
statistics analyses that are critical to get good performance with PostgreSQL.
VACUUM() is also needed after adding a lot of new rows to a
table. On a busy system with lots of changes, VACUUM() must be
run very frequently, in the worst cases even many times a day. During the
VACUUM() run, which may take hours if the database is big, the
database is from a production standpoint, practically dead. The PostgreSQL
team has fixing this on their TODO, but we assume that this is not an easy
thing to fix permanently.
PostgreSQL.
ALTER TABLE.
HEAP
tables or disk based MyISAM. See section 7
MySQL Table Types.
InnoDB and BerkeleyDB. Because every
transaction engine performs differently under different conditions, this gives
the application writer more options to find an optimal solution for his or her
setup, if need be per individual table. See section 7
MySQL Table Types.
MERGE tables gives you a unique way to instantly make a view
over a set of identical tables and use these as one. This is perfect for
systems where you have log files that you order for example by month. See
section 7.2 MERGE
Tables.
INSERT, SELECT, and
UPDATE/DELETE grants per user on a database or a table, MySQL
allows you to define a full set of different privileges on database, table and
column level. MySQL also allows you to specify the privilege on host and user
combinations. See section 4.3.1
GRANT and REVOKE Syntax.
Drawbacks with MySQL compared to PostgreSQL:
MyISAM
tables, is in many cases faster than page locks, row locks or versioning. The
drawback however is that if one doesn't take into account how table locks
work, a single long-running query can block a table for updates for a long
time. This can usually be avoided when designing the application. If not, one
can always switch the trouble table to use one of the transactional table
types. See section 5.3.2
Table Locking Issues.
UPDATE and in
MySQL 4.1 with subselects. In MySQL 4.0 one can use multi-table deletes to
delete from many tables at the same time. See section 6.4.6
DELETE Syntax. PostgreSQL currently offers the following advantages over MySQL:
Note that because we know the MySQL road map, we have included in the following table the version when MySQL should support this feature. Unfortunately we couldn't do this for previous comparison, because we don't know the PostgreSQL roadmap.
| Feature | MySQL version |
| Subselects | 4.1 |
| Foreign keys | 4.0 and 4.1 |
| Views | 4.2 |
| Stored procedures | 4.1 |
| Extensible type system | Not planned |
| Unions | 4.0 |
| Full join | 4.0 or 4.1 |
| Triggers | 4.1 |
| Constraints | 4.1 |
| Cursors | 4.1 or 4.2 |
| Extensible index types like R-trees | R-trees are planned for 4.2 |
| Inherited tables | Not planned |
Other reasons someone may consider for using PostgreSQL:
Drawbacks with PostgreSQL compared to MySQL:
VACUUM() makes PostgreSQL hard to use in a 24/7 environment.
INSERT, DELETE, and
UPDATE. For a complete list of drawbacks, you should also examine the first table in this section.
The only open source benchmark that we know of that can be used to benchmark MySQL and PostgreSQL (and other databases) is our own. It can be found at http://mysql.com/information/benchmarks.html.
We have many times asked the PostgreSQL developers and some PostgreSQL users to help us extend this benchmark to make it the definitive benchmark for databases, but unfortunately we haven't gotten any feedback for this.
We the MySQL developers have, because of this, spent a lot of hours to get maximum performance from PostgreSQL for the benchmarks, but because we don't know PostgreSQL intimately, we are sure that there are things that we have missed. We have on the benchmark page documented exactly how we did run the benchmark so that it should be easy for anyone to repeat and verify our results.
The benchmarks are usually run with and without the --fast
option. When run with --fast we are trying to use every trick the
server can do to get the code to execute as fast as possible. The idea is that
the normal run should show how the server would work in a default setup and the
--fast run shows how the server would do if the application
developer would use extensions in the server to make his application run faster.
When running with PostgreSQL and --fast we do a
VACUUM() after every major table UPDATE and DROP
TABLE to make the database in perfect shape for the following
SELECTs. The time for VACUUM() is measured separately.
When running with PostgreSQL 7.1.1 we could, however, not run with
--fast because during the INSERT test, the postmaster
(the PostgreSQL deamon) died and the database was so corrupted that it was
impossible to restart postmaster. After this happened twice, we decided to
postpone the --fast test until next PostgreSQL release. The details
about the machine we run the benchmark can be found on the benchmark page.
Before going to the other benchmarks we know of, we would like to give some background on benchmarks:
It's very easy to write a test that shows any database to be the best database in the world, by just restricting the test to something the database is very good at and not testing anything that the database is not good at. If one, after doing this, summarises the result with as a single figure, things are even easier.
This would be like us measuring the speed of MySQL compared to PostgreSQL by looking at the summary time of the MySQL benchmarks on our web page. Based on this MySQL would be more than 40 times faster than PostgreSQL, something that is of course not true. We could make things even worse by just taking the test where PostgreSQL performs worst and claim that MySQL is more than 2000 times faster than PostgreSQL.
The case is that MySQL does a lot of optimisations that PostgreSQL doesn't do. This is of course also true the other way around. An SQL optimiser is a very complex thing, and a company could spend years on just making the optimiser faster and faster.
When looking at the benchmark results you should look for things that you do in your application and just use these results to decide which database would be best suited for your application. The benchmark results also shows things a particular database is not good at and should give you a notion about things to avoid and what you may have to do in other ways.
We know of two benchmark tests that claims that PostgreSQL performs better than MySQL. These both where multi-user tests, a test that we here at MySQL AB haven't had time to write and include in the benchmark suite, mainly because it's a big task to do this in a manner that is fair against all databases.
One is the benchmark paid for by Great Bridge, the company that for 16 months attempted to build a business based on PostgreSQL but now has ceased operations. This is the probably worst benchmark we have ever seen anyone conduct. This was not only tuned to only test what PostgreSQL is absolutely best at, it was also totally unfair against every other database involved in the test.
Note: We know that even some of the main PostgreSQL developers did not like the way Great Bridge conducted the benchmark, so we don't blame the PostgreSQL team for the way the benchmark was done.
This benchmark has been condemned in a lot of postings and newsgroups so we will here just shortly repeat some things that were wrong with it.
VACUUM() before the test) and tuned the startup for the
tests, something they hadn't done for any of the other databases involved. To
say ``This process optimises indexes and frees up disk space a bit. The
optimised indexes boost performance by some margin.'' Our benchmarks clearly
indicate that the difference in running a lot of selects on a database with
and without VACUUM() can easily differ by a factor of ten.
SELECTs and JOINs (especially after a
VACUUM()), but doesn't perform as well on INSERTs or
UPDATEs. The benchmarks seem to indicate that only
SELECTs were done (or very few updates). This could easily
explain they good results for PostgreSQL in this test. The bad results for
MySQL will be obvious a bit down in this document.
Tim Perdue, a long time PostgreSQL fan and a reluctant MySQL user published a comparison on PHPbuilder (http://www.phpbuilder.com/columns/tim20001112.php3).
When we became aware of the comparison, we phoned Tim Perdue about this because there were a lot of strange things in his results. For example, he claimed that MySQL had a problem with five users in his tests, when we know that there are users with similar machines as his that are using MySQL with 2000 simultaneous connections doing 400 queries per second. (In this case the limit was the web bandwidth, not the database.)
It sounded like he was using a Linux kernel that either had some problems with many threads, such as kernels before 2.4, which had a problem with many threads on multi-CPU machines. We have documented in this manual how to fix this and Tim should be aware of this problem.
The other possible problem could have been an old glibc library and that Tim didn't use a MySQL binary from our site, which is linked with a corrected glibc library, but had compiled a version of his own with. In any of the above cases, the symptom would have been exactly what Tim had measured.
We asked Tim if we could get access to his data so that we could repeat the benchmark and if he could check the MySQL version on the machine to find out what was wrong and he promised to come back to us about this. He has not done that yet.
Because of this we can't put any trust in this benchmark either :(
Over time things also changes and the above benchmarks are not that relevant anymore. MySQL now have a couple of different table handlers with different speed/concurrency tradeoffs. See section 7 MySQL Table Types. It would be interesting to see how the above tests would run with the different transactional table types in MySQL. PostgreSQL has of course also got new features since the test was made. As the above test are not publicly available there is no way for us to know how the database would preform in the same tests today.
Conclusion:
The only benchmarks that exist today that anyone can download and run against MySQL and PostgreSQL is the MySQL benchmarks. We here at MySQL believe that open source databases should be tested with open source tools! This is the only way to ensure that no one does tests that nobody can reproduce and use this to claim that a database is better than another. Without knowing all the facts it's impossible to answer the claims of the tester.
The thing we find strange is that every test we have seen about PostgreSQL, that is impossible to reproduce, claims that PostgreSQL is better in most cases while our tests, which anyone can reproduce, clearly shows otherwise. With this we don't want to say that PostgreSQL isn't good at many things (it is!) or that it isn't faster than MySQL under certain conditions. We would just like to see a fair test where they are very good so that we could get some friendly competition going!
For more information about our benchmarks suite See section 5.1.4 The MySQL Benchmark Suite.
We are working on an even better benchmark suite, including multi user tests, and a better documentation of what the individual tests really do and how to add more tests to the suite.
This chapter describes how to obtain and install MySQL:
The recommended way to install MySQL on Linux is by using an RPM file. The
MySQL RPMs are currently being built on a RedHat Version 6.2 system but should
work on other versions of Linux that support rpm and use
glibc.
If you have problems with an RPM file, for example, if you receive the error
``Sorry, the host 'xxxx' could not be looked up'', see section 2.6.1.1
Linux Notes for Binary Distributions.
The RPM files you may want to use are:
MySQL-VERSION.i386.rpm The MySQL server. You will need this
unless you only want to connect to a MySQL server running on another machine.
MySQL-client-VERSION.i386.rpm The standard MySQL client
programs. You probably always want to install this package.
MySQL-bench-VERSION.i386.rpm Tests and benchmarks. Requires
Perl and msql-mysql-modules RPMs.
MySQL-devel-VERSION.i386.rpm Libraries and include files
needed if you want to compile other MySQL clients, such as the Perl modules.
MySQL-VERSION.src.rpm This contains the source code for all
of the above packages. It can also be used to try to build RPMs for other
architectures (for example, Alpha or SPARC). To see all files in an RPM package, run:
shell> rpm -qpl MySQL-VERSION.i386.rpm
To perform a standard minimal installation, run:
shell> rpm -i MySQL-VERSION.i386.rpm MySQL-client-VERSION.i386.rpm
To install just the client package, run:
shell> rpm -i MySQL-client-VERSION.i386.rpm
The RPM places data in `/var/lib/mysql'. The RPM also creates the appropriate entries in `/etc/rc.d/' to start the server automatically at boot time. (This means that if you have performed a previous installation, you may want to make a copy of your previously installed MySQL startup file if you made any changes to it, so you don't lose your changes.)
After installing the RPM file(s), the mysqld daemon should be
running and you should now be able to start using MySQL. See section 2.4
Post-installation Setup and Testing.
If something goes wrong, you can find more information in the binary installation chapter. See section 2.2.7 Installing a MySQL Binary Distribution.
The MySQL server for Windows is available in two distribution types:
Generally speaking, you should use the binary distribution.
You will need the following:
ZIP program to unpacked the distribution file.
ODBC, you will
also need the MyODBC driver. See section 8.3 MySQL
ODBC Support. C:\> NET STOP MySQLOtherwise, use:
C:\mysql\bin> mysqladmin -u root shutdown
C:\mysql\bin> mysqld-max-nt --remove
Browse button to specify your
preferred directory.
Starting with MySQL 3.23.38, the Windows distribution includes both the normal and the MySQL-Max server binaries. Here is a list of the different MySQL servers you can use:
| Binary | Description |
mysqld |
Compiled with full debugging and automatic memory allocation checking, symbolic links, InnoDB and BDB tables. |
mysqld-opt |
Optimised binary with no support for transactional tables. |
mysqld-nt |
Optimised binary for NT with support for named pipes. You can run this version on Win98, but in this case no named pipes are created and you must have TCP/IP installed. |
mysqld-max |
Optimised binary with support for symbolic links, InnoDB and BDB tables. |
mysqld-max-nt |
Like mysqld-max, but compiled with support for named
pipes. |
All of the above binaries are optimised for the Pentium Pro processor but should work on any Intel processor >= i386.
In the following circumstances you will need to use the MySQL configuration file:
There are two configuration files with the same function: `my.cnf'
and `my.ini' file, however please note that only of one these should
can used. Both files are plain text. The `my.cnf' file should be
created in the root directory of drive C and the `my.ini' file on the
WinDir directory e.g: `C:\WINDOWS' or `C:\WINNT'. If your PC
uses a boot loader where the C drive isn't the boot drive, then your only option
is to use the `my.ini' file. Also note that if you use the
WinMySQLAdmin tool, only the `my.ini' file is used. The
`\mysql\bin' directory contains a help file with instructions for using
this tool.
Using notepad.exe, create the configuration file and edit the
base section and keys:
[mysqld] basedir=the_install_path #e.g. c:/mysql datadir=the_data_path #e.g. c:/mysql/data or d:/mydata/data
If the data directory is other than the default `c:\mysql\data', you must cut the whole `\data\mysql' directory and paste it on the your option new directory, e.g.: `d:\mydata\mysql'.
If you want to use the InnoDB transactional tables, you need to
manually create two new directories to hold the InnoDB data and log files, e.g.
`c:\ibdata' and `c:\iblogs'. You will also need to add some
extra lines to the configuration file. See section 7.5.2
InnoDB Startup Options.
If you don't want to use InnoDB tables, add the
skip-innodb option to the configuration file.
Now you are ready to test starting the server.
Testing from a DOS command prompt is the best thing to do because the server prints messages, so if something is wrong with your configuration you will see a more accurate error message which will make it easier for you to identify and fix any problems.
Make sure you are in the right directory, then enter:
C:\mysql\bin> mysqld-max --standalone
You should see the below print messages:
InnoDB: The first specified data file c:\ibdata\ibdata1 did not exist: InnoDB: a new database to be created! InnoDB: Setting file c:\ibdata\ibdata1 size to 209715200 InnoDB: Database physically writes the file full: wait... InnoDB: Log file c:\iblogs\ib_logfile0 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile0 size to 31457280 InnoDB: Log file c:\iblogs\ib_logfile1 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile1 size to 31457280 InnoDB: Log file c:\iblogs\ib_logfile2 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile2 size to 31457280 InnoDB: Doublewrite buffer not found: creating new InnoDB: Doublewrite buffer created InnoDB: creating foreign key constraint system tables InnoDB: foreign key constraint system tables created 011024 10:58:25 InnoDB: Started
For further information about running MySQL on Windows, see section 2.6.2 Windows Notes.
Check the MySQL homepage (http://mysql.com/) for information about the current version and for downloading instructions.
Our main download mirror is located at:
http://mirrors.sunsite.dk/mysql/
If you are interested in becoming a MySQL mirror site, you may anonymously
rsync with: rsync://sunsite.dk/ftp/mirrors/mysql/. Please send
e-mail to webmaster@mysql.com notifying
us of your mirror to be added to the list below.
If you have problems downloading from our main site, try using one of the mirrors listed below.
Please report bad or out-of-date mirrors to webmaster@mysql.com.
Europe:
Austria [Univ. of
Technology/Vienna] @ WWW (http://gd.tuwien.ac.at/db/mysql/)
FTP (ftp://gd.tuwien.ac.at/db/mysql/)
Belgium [BELNET] @ WWW
(http://mysql.belnet.be/) FTP (ftp://ftp.belnet.be/mirror/ftp.mysql.com/pub/mysql/)
Bulgaria
[online.bg/Sofia] @ WWW (http://mysql.online.bg/) FTP (ftp://mysql.online.bg/)
Czech Republic
[Masaryk University in Brno] @ WWW (http://mysql.linux.cz/) FTP (ftp://ftp.fi.muni.cz/pub/mysql/)
Czech Republic
[www.gin.cz] @ WWW (http://mysql.gin.cz/)
FTP (ftp://ftp.gin.cz/pub/MIRRORS/www.mysql.com/)
Czech Republic
[www.sopik.cz] @ WWW (http://www.mysql.cz/)
Denmark [Borsen] @ WWW
(http://mysql.borsen.dk/)
Denmark [SunSITE] @ WWW
(http://mirrors.sunsite.dk/mysql/)
FTP (ftp://sunsite.dk/mirrors/mysql/)
Estonia [OK
Interactive] @ WWW (http://mysql.mirror.ok.ee/)
Finland [KPNQwest] @
WWW (http://mysql.kpnqwest.fi/)
Finland [tonnikala.net]
@ WWW (http://mysql.tonnikala.org/)
France [fastorama.com,
Chatenois] @ WWW (http://mysql.fastorama.com/) FTP (ftp://ftp.fastorama.com/unix/mysql/)
France [mtesa.net] @ WWW
(http://mysql.mtesa.net/)
France [Omegatomic] @
WWW (http://mysql.omegatomic.com/)
Germany [GWDG] @ WWW
(http://ftp.gwdg.de/pub/misc/mysql/)
FTP (ftp://ftp.gwdg.de/pub/misc/mysql/)
Germany
[Kernelnotes.de, Bonn] @ WWW (http://www.kernelnotes.de/mysql/)
FTP (ftp://ftp.kernelnotes.de/mysql.com/)
Germany [SunSITE
Central Europe] @ WWW (http://sunsite.informatik.rwth-aachen.de/mysql/)
FTP (ftp://sunsite.informatik.rwth-aachen.de/pub/mirror/www.mysql.com/)
Germany [Wolfenbuettel]
@ WWW (http://www.fh-wolfenbuettel.de/ftp/pub/database/mysql/)
FTP (ftp://ftp.fh-wolfenbuettel.de/pub/database/mysql/)
Greece [NTUA, Athens] @
WWW (http://www.ntua.gr/mysql/) FTP
(ftp://ftp.ntua.gr/pub/databases/mysql/)
Hungary [stop.hu] @ WWW
(http://mysql.mirror.stop.hu/)
Hungary [TiszaneT] @
WWW (http://mysql.tiszanet.hu/) FTP
(ftp://mysql.tiszanet.hu/pub/mirrors/mysql/)
Hungary [Xenia] @ WWW
(http://mysql.sote.hu/) FTP (ftp://xenia.sote.hu/pub/mirrors/www.mysql.com/)
Iceland [GM] @ WWW (http://mysql.gm.is/) FTP (ftp://ftp.gm.is/pub/mysql/)
Ireland [Esat Net] @
WWW (http://ftp.esat.net/mirrors/download.sourceforge.net/pub/mirrors/mysql/)
FTP (ftp://ftp.esat.net/mirrors/download.sourceforge.net/pub/mirrors/mysql/)
Italy [feelinglinux.com]
@ WWW (http://mysql.feelinglinux.com/)
Italy [Teta Srl] @ WWW
(http://www.teta.it/mysql/)
Italy [tzone.it] @ WWW
(http://mysql.tzone.it/)
Latvia [linux.lv] @ FTP
(ftp://ftp.linux.lv/pub/software/mysql/)
Netherlands
[OMS-Net] @ WWW (http://mysql.oms-net.nl/)
Netherlands
[ProServe] @ WWW (http://mysql.proserve.nl/)
Netherlands [WideXS
BV] @ WWW (http://mysql.mirror.widexs.nl/) FTP
(ftp://mirror.widexs.nl/pub/mysql/)
Poland
[ncservice.com/Gdansk] @ WWW (http://mysql.service.net.pl/)
Poland [SunSITE] @ WWW
(http://sunsite.icm.edu.pl/mysql/)
FTP (ftp://sunsite.icm.edu.pl/pub/unix/mysql/)
Portugal [Instituto
Supertior Técnico] @ WWW (http://darkstar.ist.utl.pt/mysql/)
FTP (ftp://darkstar.ist.utl.pt/pub/mysql/)
Portugal [Netc] @ WWW
(http://ftp.netc.pt/pub/mysql/)
FTP (ftp://ftp.netc.pt/pub/mysql/)
Romania
[roedu.net/Bucharest] @ FTP (ftp://ftp.roedu.net/pub/mirrors/ftp.mysql.com/)
Russia [DirectNet] @ WWW
(http://mysql.directnet.ru/) FTP (ftp://ftp.dn.ru/pub/MySQL/)
Russia [Scientific
Center/Chernogolovka] @ FTP (ftp://ftp.chg.ru/pub/databases/mysql/)
Spain [GMC Control
Systems] @ WWW (http://mysql.neptuno2000.com/) FTP
(ftp://ftp.neptuno2000.com/pub/mysql/)
Sweden [Sunet] @ WWW (http://ftp.sunet.se/pub/unix/databases/relational/mysql/)
FTP (ftp://ftp.sunet.se/pub/unix/databases/relational/mysql/)
Switzerland
[SunSITE] @ WWW (http://sunsite.cnlab-switch.ch/ftp/mirror/mysql/)
FTP (ftp://sunsite.cnlab-switch.ch/mirror/mysql/)
Turkey [proGEN] @ WWW
(http://mysql.progen.com.tr/)
UK [PLiG/UK] @
WWW (http://ftp.plig.org/pub/mysql/) FTP
(ftp://ftp.plig.org/pub/mysql/)
Ukraine [ISP Alkar
Teleport/Dnepropetrovsk] @ WWW (http://mysql.dp.ua/) FTP (ftp://ftp.tlk-l.net/pub/mirrors/mysql.com/)
Ukraine [PACO] @ WWW
(http://mysql.paco.net.ua/) FTP (ftp://mysql.paco.net.ua/)
Yugoslavia
[bolex.co.yu] @ WWW (http://mysql.boa.org.yu/) FTP (ftp://ftp.linux.org.yu/pub/MySQL/)
North America:
Canada [Tryc] @ WWW (http://web.tryc.on.ca/mysql/)
Mexico [UAM] @ WWW (http://mysql.azc.uam.mx/) FTP (ftp://mysql.azc.uam.mx/mirrors/mysql/)
Mexico [UNAM] @ WWW (http://mysql.unam.mx/) FTP (ftp://mysql.unam.mx/pub/mysql/)
USA [adgrafix.com/Boston,
MA] @ WWW (http://mysql.adgrafix.com/)
USA [Ahaza Systems/Seattle,
WA] @ WWW (http://mysql.mirrortree.com/) FTP (ftp://mysql.mirrortree.com/pub/mysql/)
USA [Hurricane Electric/San
Jose] @ WWW (http://mysql.he.net/)
USA [netNumina/Cambridge,
MA] @ WWW (http://mysql.mirrors.netnumina.com/)
USA [NIXC/Vienna, VA] @ WWW
(http://mysql.nixc.net/) FTP (ftp://mysql.nixc.net/pub/mysql/)
USA [University of
Wisconsin/Wisconsin] @ WWW (http://mirror.sit.wisc.edu/mysql/)
FTP (ftp://mirror.sit.wisc.edu/mirrors/mysql/)
USA [ValueClick, Los
Angeles CA] @ WWW (http://mysql.valueclick.com/) FTP (ftp://mysql.valueclick.com/pub/mysql/Downloads/)
South America:
Argentina
[bannerlandia.com] @ WWW (http://mysql.bannerlandia.com.ar/)
FTP (ftp://mysql.bannerlandia.com.ar/mirrors/mysql/)
Chile [PSINet] @ WWW (http://mysql.psinet.cl/) FTP (ftp://ftp.psinet.cl/pub/database/mysql/)
Chile [Tecnoera] @ WWW
(http://mysql.tecnoera.com/)
Chile [Vision] @ WWW (http://mysql.vision.cl/) Asia:
China [Gremlins/Hong
Kong] @ WWW (http://mysql.gremlins.com.hk/) FTP
(ftp://ftp.mirrors.gremlins.com.hk/mysql/)
China [HKLPG/Hong Kong] @
WWW (http://mysql.hklpg.org/)
China [linuxforum.net] @
FTP (http://www2.linuxforum.net/mirror/mysql/)
China [shellhung.org/Hong
Kong] @ WWW (http://mysql.shellhung.org/) FTP (ftp://ftp.shellhung.org/pub/Mirror/mysql/)
Indonesia [incaf.net]
@ WWW (http://mysql.incaf.net/)
Indonesia [web.id] @
WWW (http://mysql.itb.web.id/) FTP (ftp://mysql.itb.web.id/pub/MySQL/)
Japan [Soft Agency] @ WWW
(http://www.softagency.co.jp/MySQL/)
Japan [u-aizu.ac.jp/Aizu]
@ FTP (ftp://ftp.u-aizu.ac.jp/ftp/pub/dbms/mysql/mysql.com/)
Philippines [Ateneo
de Zamboanga University] @ WWW (http://mysql.adzu.edu.ph/)
Singapore [HJC] @ WWW
(http://mysql.hjc.edu.sg/) FTP (ftp://ftp.hjc.edu.sg/mysql/)
South Korea
[PanworldNet] @ WWW (http://mysql.holywar.net/)
South Korea
[Webiiz] @ WWW (http://mysql.webiiz.com/)
Taiwan
[nctu.edu/HsinChu] @ WWW (http://mysql.nctu.edu.tw/)
Taiwan [TTN] @ WWW (http://mysql.ttn.net/) Australia:
Australia
[planetmirror.com] @ WWW (http://mysql.planetmirror.com/) FTP
(ftp://planetmirror.com/pub/mysql/)
Africa:
South African
Republic [Mweb] @ WWW (http://www.mysql.mweb.co.za/)
South African
Republic [The Internet Solution/Johannesburg] @ FTP (ftp://ftp.is.co.za/linux/mysql/)
We use GNU Autoconf, so it is possible to port MySQL to all modern systems with working Posix threads and a C++ compiler. (To compile only the client code, a C++ compiler is required but not threads.) We use and develop the software ourselves primarily on Sun Solaris (Versions 2.5 - 2.7) and SuSE Linux Version 7.x.
Note that for many operating systems, the native thread support works only in the latest versions. MySQL has been reported to compile successfully on the following operating system/thread package combinations:
glibc 2.0.7+. See
section 2.6.1 Linux
Notes (All Linux Versions).
Note that not all platforms are suited equally well for running MySQL. How well a certain platform is suited for a high-load mission critical MySQL server is determined by the following factors:
pthread_mutex_lock() is too anxious to yield CPU, this will hurt
MySQL tremendously. If this issue is not taken care of, adding extra CPUs will
actually make MySQL slower.
Based on the above criteria, the best platforms for running MySQL at this point are x86 with SuSE Linux 7.1, 2.4 kernel and ReiserFS (or any similar Linux distribution) and Sparc with Solaris 2.7 or 2.8. FreeBSD comes third, but we really hope it will join the top club once the thread library is improved. We also hope that at some point we will be able to include all other platforms on which MySQL compiles, runs okay, but not quite with the same level of stability and performance, into the top category. This will require some effort on our part in cooperation with the developers of the OS/library components MySQL depends upon. If you are interested in making one of those components better, are in a position to influence their development, and need more detailed instructions on what MySQL needs to run better, send an e-mail to internals@lists.mysql.com.
Please note that the comparison above is not to say that one OS is better or worse than the other in general. We are talking about choosing a particular OS for a dedicated purpose - running MySQL, and compare platforms in that regard only. With this in mind, the result of this comparison would be different if we included more issues into it. And in some cases, the reason one OS is better than the other could simply be that we have put forth more effort into testing on and optimising for that particular platform. We are just stating our observations to help you make a decision on which platform to use MySQL on in your setup.
The first decision to make is whether you want to use the latest development release or the last stable release:
The second decision to make is whether you want to use a source distribution or a binary distribution. In most cases you should probably use a binary distribution, if one exists for your platform, as this generally will be easier to install than a source distribution.
In the following cases you probably will be better off with a source installation:
MySQL clients can
connect to both MySQL versions. The extended MySQL binary distribution is
marked with the -max suffix and is configured with the same
options as mysqld-max. See section 4.7.5
mysqld-max, An extended mysqld server. If you want to use the
MySQL-Max RPM, you must first install the standard
MySQL RPM.
mysqld with some extra features that
are not in the standard binary distributions. Here is a list of the most
common extra options that you may want to use:
--with-innodb
--with-berkeley-db
--with-raid
--with-libwrap
--with-named-z-lib (This is done for some of the binaries)
--with-debug[=full] pgcc) or use compiler options that are better optimised for
your processor.
The MySQL naming scheme uses release numbers that consist of three numbers
and a suffix. For example, a release name like mysql-3.21.17-beta
is interpreted like this:
3) describes the file format. All Version 3
releases have the same file format.
21) is the release level. Normally there
are two to choose from. One is the release/stable branch (currently
23) and the other is the development branch (currently
4.0). Normally both are stable, but the development version may
have quirks, missing documentation on new features, or may fail to compile on
some systems.
17) is the version number within the
release level. This is incremented for each new distribution. Usually you want
the latest version for the release level you have chosen.
beta) indicates the stability level of the
release. The possible suffixes are:
alpha indicates that the release contains some large
section of new code that hasn't been 100% tested. Known bugs (usually there
are none) should be documented in the News section. See section D MySQL
change history. There are also new commands and extensions in most alpha
releases. Active development that may involve major code changes can occur
on an alpha release, but everything will be tested before doing a release.
There should be no known bugs in any MySQL release.
beta means that all new code has been tested. No major new
features that could cause corruption on old code are added. There should be
no known bugs. A version changes from alpha to beta when there haven't been
any reported fatal bugs within an alpha version for at least a month and we
don't plan to add any features that could make any old command more
unreliable.
gamma is a beta that has been around a while and seems to
work fine. Only minor fixes are added. This is what many other companies
call a release.
All versions of MySQL are run through our standard tests and benchmarks to ensure that they are relatively safe to use. Because the standard tests are extended over time to check for all previously found bugs, the test suite keeps getting better.
Note that all releases have been tested at least with:
crash-me test
Another test is that we use the newest MySQL version in our internal production environment, on at least one machine. We have more than 100 gigabytes of data to work with.
This section describes the default layout of the directories created by installing binary and source distributions.
A binary distribution is installed by unpacking it at the installation location you choose (typically `/usr/local/mysql') and creates the following directories in that location:
| Directory | Contents of directory |
| `bin' | Client programs and the mysqld server |
| `data' | Log files, databases |
| `include' | Include (header) files |
| `lib' | Libraries |
| `scripts' | mysql_install_db |
| `share/mysql' | Error message files |
| `sql-bench' | Benchmarks |
A source distribution is installed after you configure and compile it. By default, the installation step installs files under `/usr/local', in the following subdirectories:
| Directory | Contents of directory |
| `bin' | Client programs and scripts |
| `include/mysql' | Include (header) files |
| `info' | Documentation in Info format |
| `lib/mysql' | Libraries |
| `libexec' | The mysqld server |
| `share/mysql' | Error message files |
| `sql-bench' | Benchmarks and crash-me test |
| `var' | Databases and log files |
Within an installation directory, the layout of a source installation differs from that of a binary installation in the following ways:
mysqld server is installed in the `libexec'
directory rather than in the `bin' directory.
mysql_install_db is installed in the
`/usr/local/bin' directory rather than in
`/usr/local/mysql/scripts'.
You can create your own binary installation from a compiled source distribution by executing the script `scripts/make_binary_distribution'.
MySQL is evolving quite rapidly here at MySQL AB and we want to share this with other MySQL users. We try to make a release when we have very useful features that others seem to have a need for.
We also try to help out users who request features that are easy to implement. We take note of what our licensed users want to have, and we especially take note of what our extended e-mail supported customers want and try to help them out.
No one has to download a new release. The News section will tell you if the new release has something you really want. See section D MySQL change history.
We use the following policy when updating MySQL:
The current stable release is Version 3.23; We have already moved active development to Version 4.0. Bugs will still be fixed in the stable version. We don't believe in a complete freeze, as this also leaves out bug fixes and things that ``must be done.'' ``Somewhat frozen'' means that we may add small things that ``almost surely will not affect anything that's already working.''
As a service, we at MySQL AB provide a set of binary distributions of MySQL that are compiled at our site or at sites where customers kindly have given us access to their machines.
These distributions are generated with
scripts/make_binary_distribution and are configured with the
following compilers and options:
gcc 2.7.2.1
CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors" ./configure
--prefix=/usr/local/mysql --disable-shared --with-extra-charsets=complex
--enable-assembler
egcs 1.0.3a or 2.90.27 or
gcc 2.95.2 and newer
CC=gcc CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors
-fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql
--with-low-memory --with-extra-charsets=complex --enable-assembler
gcc 2.8.1
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
--with-low-memory --with-extra-charsets=complex
pgcc 2.90.29 (egcs
1.0.3a)
CFLAGS="-O3 -mpentium -mstack-align-double" CXX=gcc CXXFLAGS="-O3
-mpentium -mstack-align-double -felide-constructors -fno-exceptions -fno-rtti"
./configure --prefix=/usr/local/mysql --enable-assembler
--with-mysqld-ldflags=-all-static --with-extra-charsets=complex
gcc 2.95.2
CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro
-felide-constructors -fno-exceptions -fno-rtti" ./configure
--prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static
--disable-shared --with-extra-charset=complex
gcc 2.7-95q4
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
--with-extra-charsets=complex
gcc 2.7.2.2
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
--with-extra-charsets=complex
gcc 2.8.1
CC=gcc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 ./configure
--prefix=/usr/local/mysql --with-low-memory
--with-extra-charsets=complex
gcc 2.8.0
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
--with-extra-charsets=complex
gcc 2.7.2.1
CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql
--with-extra-charsets=complex
gcc 2.7.2
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
--with-extra-charsets=complex Anyone who has more optimal options for any of the configurations listed above can always mail them to the developer's mailing list at internals@lists.mysql.com.
RPM distributions prior to MySQL Version 3.22 are user-contributed. Beginning with Version 3.22, the RPMs are generated by us at MySQL AB.
If you want to compile a debug version of MySQL, you should add
--with-debug or --with-debug=full to the above
configure lines and remove any -fomit-frame-pointer options.
For the Windows distribution, please see section 2.1.2 Installing MySQL on Windows.
See also section 2.1.2.1 Installing the Binaries, section 2.1.1 Installing MySQL on Linux, and section 8.4.7 Building Client Programs.
You need the following tools to install a MySQL binary distribution:
gunzip to uncompress the distribution.
tar to unpack the distribution. GNU
tar is known to work. Sun tar is known to have
problems. An alternative installation method under Linux is to use RPM (RedHat Package Manager) distributions. See section 2.1.1 Installing MySQL on Linux.
If you run into problems, please always use
mysqlbug when posting questions to mysql@lists.mysql.com. Even if the
problem isn't a bug, mysqlbug gathers system information that will
help others solve your problem. By not using mysqlbug, you lessen
the likelihood of getting a solution to your problem! You will find
mysqlbug in the `bin' directory after you unpack the
distribution. See section 1.6.2.3
How to Report Bugs or Problems.
The basic commands you must execute to install and use a MySQL binary distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> cd /usr/local shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysql shell> cd mysql shell> scripts/mysql_install_db shell> chown -R root /usr/local/mysql shell> chown -R mysql /usr/local/mysql/data shell> chgrp -R mysql /usr/local/mysql shell> chown -R root /usr/local/mysql/bin shell> bin/safe_mysqld --user=mysql &
You can add new users using the bin/mysql_setpermission script
if you install the DBI and Msql-Mysql-modules Perl
modules.
A more detailed description follows.
To install a binary distribution, follow the steps below, then proceed to section 2.4 Post-installation Setup and Testing, for post-installation setup and testing:
root.)
tar archives and have names like
`mysql-VERSION-OS.tar.gz', where VERSION is a number
(for example, 3.21.15), and OS indicates the type of
operating system for which the distribution is intended (for example,
pc-linux-gnu-i586).
-max prefix,
this means that the binary has support for transaction-safe tables and other
features. See section 4.7.5
mysqld-max, An extended mysqld server. Note that all binaries are built
from the same MySQL source distribution.
mysqld to run as: shell> groupadd mysql shell> useradd -g mysql mysqlThese commands add the
mysql group and the
mysql user. The syntax for useradd and
groupadd may differ slightly on different versions of Unix. They
may also be called adduser and addgroup. You may
wish to call the user and group something else instead of mysql.
shell> cd /usr/local
shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysqlThe first command creates a directory named `mysql-VERSION-OS'. The second command makes a symbolic link to that directory. This lets you refer more easily to the installation directory as `/usr/local/mysql'.
shell> cd mysqlYou will find several files and subdirectories in the
mysql
directory. The most important for installation purposes are the `bin'
and `scripts' subdirectories.
PATH environment variable so that your shell finds the
MySQL programs properly. See section F
Environment Variables.
mysql_install_db script used to
initialise the mysql database containing the grant tables that
store the server access permissions. mysqlaccess and have the MySQL
distribution in some non-standard place, you must change the location where
mysqlaccess expects to find the mysql client. Edit
the `bin/mysqlaccess' script at approximately line 18. Search for a
line that looks like this: $MYSQL = '/usr/local/bin/mysql'; # path to mysql executableChange the path to reflect the location where
mysql
actually is stored on your system. If you do not do this, you will get a
Broken pipe error when you run mysqlaccess.
shell> scripts/mysql_install_dbNote that MySQL versions older than Version 3.22.10 started the MySQL server when you run
mysql_install_db. This is no longer true!
root and ownership of the
data directory to the user that you will run mysqld as: shell> chown -R root /usr/local/mysql shell> chown -R mysql /usr/local/mysql/data shell> chgrp -R mysql /usr/local/mysqlThe first command changes the
owner attribute of the files
to the root user, the second one changes the owner
attribute of the data directory to the mysql user, and the third
one changes the group attribute to the mysql group.
DBI/DBD interface, see section 2.7
Perl Installation Comments.
support-files/mysql.server to the location where
your system has its startup files. More information can be found in the
support-files/mysql.server script itself and in section 2.4.3
Starting and Stopping MySQL Automatically. After everything has been unpacked and installed, you should initialise and test your distribution.
You can start the MySQL server with the following command:
shell> bin/safe_mysqld --user=mysql &
See section 4.7.2 safe_mysqld, the wrapper around mysqld.
See section 2.4 Post-installation Setup and Testing.
Before you proceed with the source installation, check first to see if our binary is available for your platform and if it will work for you. We put in a lot of effort into making sure that our binaries are built with the best possible options.
You need the following tools to build and install MySQL from source:
gunzip to uncompress the distribution.
tar to unpack the distribution. GNU
tar is known to work. Sun tar is known to have
problems.
gcc >= 2.95.2,
egcs >= 1.0.2 or egcs 2.91.66, SGI C++, and
SunPro C++ are some of the compilers that are known to work.
libg++ is not needed when using gcc.
gcc 2.7.x has a bug that makes it impossible to compile some
perfectly legal C++ files, such as `sql/sql_base.cc'. If you only
have gcc 2.7.x, you must upgrade your gcc to be able
to compile MySQL. gcc 2.8.1 is also known to have problems on
some platforms so it should be avoided if there exists a new compiler for the
platform.. gcc >= 2.95.2 is recommended when compiling MySQL
Version 3.23.x.
make program. GNU make is always
recommended and is sometimes required. If you have problems, we recommend
trying GNU make 3.75 or newer. If you are using a recent version of gcc, recent enough to
understand -fno-exceptions option, it is very
important that you use it. Otherwise, you may compile a binary that
crashes randomly. We also recommend that you use
-felide-contructors and -fno-rtti along with
-fno-exceptions. When in doubt, do the following:
CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static
On most systems this will give you a fast and stable binary.
If you run into problems, please always use
mysqlbug when posting questions to mysql@lists.mysql.com. Even if the
problem isn't a bug, mysqlbug gathers system information that will
help others solve your problem. By not using mysqlbug, you lessen
the likelihood of getting a solution to your problem! You will find
mysqlbug in the `scripts' directory after you unpack the
distribution. See section 1.6.2.3
How to Report Bugs or Problems.
The basic commands you must execute to install a MySQL source distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> gunzip < mysql-VERSION.tar.gz | tar -xvf - shell> cd mysql-VERSION shell> ./configure --prefix=/usr/local/mysql shell> make shell> make install shell> scripts/mysql_install_db shell> chown -R root /usr/local/mysql shell> chown -R mysql /usr/local/mysql/var shell> chgrp -R mysql /usr/local/mysql shell> cp support-files/my-medium.cnf /etc/my.cnf shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &
If you want have support for InnoDB tables, you should edit the
/etc/my.cnf file and remove the # character before the
parameters that starts with innodb_.... See section 4.1.2
my.cnf Option Files. See section 7.5.2
InnoDB Startup Options.
If you start from a source RPM, then do the following:
shell> rpm --rebuild MySQL-VERSION.src.rpm
This will make a binary RPM that you can install.
You can add new users using the bin/mysql_setpermission script
if you install the DBI and Msql-Mysql-modules Perl
modules.
A more detailed description follows.
To install a source distribution, follow the steps below, then proceed to section 2.4 Post-installation Setup and Testing, for post-installation initialisation and testing:
tar archives and have names like `mysql-VERSION.tar.gz',
where VERSION is a number like 4.0.1-alpha.
mysqld to run as: shell> groupadd mysql shell> useradd -g mysql mysqlThese commands add the
mysql group, and the
mysql user. The syntax for useradd and
groupadd may differ slightly on different versions of Unix. They
may also be called adduser and addgroup. You may
wish to call the user and group something else instead of mysql.
shell> gunzip < /path/to/mysql-VERSION.tar.gz | tar xvf -This command creates a directory named `mysql-VERSION'.
shell> cd mysql-VERSIONNote that currently you must configure and build MySQL from this top-level directory. You can not build it in a different directory.
shell> ./configure --prefix=/usr/local/mysql shell> makeWhen you run
configure, you might want to specify some
options. Run ./configure --help for a list of options. section 2.3.3
Typical configure Options, discusses some of the more useful
options. If configure fails, and you are going to send mail to mysql@lists.mysql.com to ask for
assistance, please include any lines from `config.log' that you think
can help solve the problem. Also include the last couple of lines of output
from configure if configure aborts. Post the bug
report using the mysqlbug script. See section 1.6.2.3
How to Report Bugs or Problems. If the compile fails, see section 2.3.5
Problems Compiling?, for help with a number of common problems.
shell> make installYou might need to run this command as
root.
shell> scripts/mysql_install_dbNote that MySQL versions older than Version 3.22.10 started the MySQL server when you run
mysql_install_db. This is no longer true!
root and ownership of the
data directory to the user that you will run mysqld as: shell> chown -R root /usr/local/mysql shell> chown -R mysql /usr/local/mysql/var shell> chgrp -R mysql /usr/local/mysqlThe first command changes the
owner attribute of the files
to the root user, the second one changes the owner
attribute of the data directory to the mysql user, and the third
one changes the group attribute to the mysql group.
DBI/DBD interface, see section 2.7
Perl Installation Comments.
support-files/mysql.server to the location where
your system has its startup files. More information can be found in the
support-files/mysql.server script itself and in section 2.4.3
Starting and Stopping MySQL Automatically. After everything has been installed, you should initialise and test your distribution:
shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &
If that command fails immediately with mysqld daemon ended then
you can find some information in the file
`mysql-data-directory/'hostname'.err'. The likely reason is that you
already have another mysqld server running. See section 4.1.4
Running Multiple MySQL Servers on the Same Machine.
See section 2.4 Post-installation Setup and Testing.
Sometimes patches appear on the mailing list or are placed in the patches area of the MySQL web site (http://mysql.com/Downloads/Patches/).
To apply a patch from the mailing list, save the message in which the patch appears in a file, change into the top-level directory of your MySQL source tree, and run these commands:
shell> patch -p1 < patch-file-name shell> rm config.cache shell> make clean
Patches from the FTP site are distributed as plain text files or as files
compressed with gzip. Apply a plain patch as shown above for
mailing list patches. To apply a compressed patch, change into the top-level
directory of your MySQL source tree and run these commands:
shell> gunzip < patch-file-name.gz | patch -p1 shell> rm config.cache shell> make clean
After applying a patch, follow the instructions for a normal source install,
beginning with the ./configure step. After running the make
install step, restart your MySQL server.
You may need to bring down any currently running server before you run
make install. (Use mysqladmin shutdown to do this.)
Some systems do not allow you to install a new version of a program if it
replaces the version that is currently executing.
configure OptionsThe configure script gives you a great deal of control over how
you configure your MySQL distribution. Typically you do this using options on
the configure command line. You can also affect
configure using certain environment variables. See section F
Environment Variables. For a list of options supported by
configure, run this command:
shell> ./configure --help
Some of the more commonly-used configure options are described
below:
--without-server option: shell> ./configure --without-serverIf you don't have a C++ compiler,
mysql will not compile
(it is the one client program that requires C++). In this case, you can remove
the code in configure that tests for the C++ compiler and then
run ./configure with the --without-server option.
The compile step will still try to build mysql, but you can
ignore any warnings about `mysql.cc'. (If make stops,
try make -k to tell it to continue with the rest of the build
even if errors occur.)
libmysqld.a) you
should use the --with-embedded-server option.
configure command, something
like one of these: shell> ./configure --prefix=/usr/local/mysql
shell> ./configure --prefix=/usr/local \
--localstatedir=/usr/local/mysql/data
The first command changes the installation prefix so that everything is
installed under `/usr/local/mysql' rather than the default of
`/usr/local'. The second command preserves the default installation
prefix, but overrides the default location for database directories (normally
`/usr/local/var') and changes it to
/usr/local/mysql/data. After you have compiled MySQL, you can
change these options with option files. See section 4.1.2
my.cnf Option Files.
configure command like this: shell> ./configure --with-unix-socket-path=/usr/local/mysql/tmp/mysql.sockNote that the given file must be an absolute pathname! You can also later change the location `mysql.sock' by using the MySQL option files. See section A.4.5 How to Protect or change the MySQL socket file `/tmp/mysql.sock'.
configure like this: shell> ./configure --with-client-ldflags=-all-static \
--with-mysqld-ldflags=-all-static
gcc and don't have libg++ or
libstdc++ installed, you can tell configure to use
gcc as your C++ compiler: shell> CC=gcc CXX=gcc ./configureWhen you use
gcc as your C++ compiler, it will not attempt
to link in libg++ or libstdc++. Here is some common
environment variables to set depending on the compiler you are using:
| Compiler | Recommended options |
| gcc 2.7.2.1 | CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors" |
| egcs 1.0.3a | CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" |
| gcc 2.95.2 | CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro -felide-constructors -fno-exceptions -fno-rtti" |
| pgcc 2.90.29 or newer | CFLAGS="-O3 -mpentiumpro -mstack-align-double" CXX=gcc CXXFLAGS="-O3 -mpentiumpro -mstack-align-double -felide-constructors -fno-exceptions -fno-rtti" |
--prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-staticThe full configure line would in other words be something like the following for all recent gcc versions:
CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-staticThe binaries we provide on the MySQL web site at http://mysql.com/ are all compiled with full optimisation and should be perfect for most users. See section 2.2.6 MySQL Binaries Compiled by MySQL AB. There are some things you can tweak to make an even faster binary, but this is only for advanced users. See section 5.5.3 How Compiling and Linking Affects the Speed of MySQL. If the build fails and produces errors about your compiler or linker not being able to create the shared library `libmysqlclient.so.#' (`#' is a version number), you can work around this problem by giving the
--disable-shared option to configure. In this case,
configure will not build a shared
libmysqlclient.so.# library.
DEFAULT column values for
non-NULL columns (that is, columns that are not allowed to be
NULL). This causes INSERT statements to generate an
error unless you explicitly specify values for all columns that require a
non-NULL value. To suppress use of default values, run
configure like this: shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure
--with-charset option: shell> ./configure --with-charset=CHARSET
CHARSET may be one of big5,
cp1251, cp1257, czech,
danish, dec8, dos, euc_kr,
gb2312, gbk, german1,
hebrew, hp8, hungarian,
koi8_ru, koi8_ukr, latin1,
latin2, sjis, swe7,
tis620, ujis, usa7, or
win1251ukr. See section 4.6.1
The Character Set Used for Data and Sorting. If you want to convert
characters between the server and the client, you should take a look at the
SET OPTION CHARACTER SET command. See section 5.5.6
SET Syntax. Warning: If
you change character sets after having created any tables, you will have to
run myisamchk -r -q on every table. Your indexes may be sorted
incorrectly otherwise. (This can happen if you install MySQL, create some
tables, then reconfigure MySQL to use a different character set and reinstall
it.) With the option --with-extra-charset=LIST you can define
which additional character sets should be incompiled in the server. Here
LIST is either a list of character set separated with space,
complex to include all characters that can't be dynamically
loaded or all to include all character sets into the binaries.
--with-debug
option: shell> ./configure --with-debugThis causes a safe memory allocator to be included that can find some errors and that provides output about what is happening. See section E.1 Debugging a MySQL server.
--enable-thread-safe-client configure options. This will create a
libmysqlclient_r library with which you should link your threaded
applications. See section 8.4.8
How to Make a Threaded Client.
Caution: You should read this section only if you are interested in helping us test our new code. If you just want to get MySQL up and running on your system, you should use a standard release distribution (either a source or binary distribution will do).
To obtain our most recent development source tree, use these instructions:
shell> bk clone bk://work.mysql.com:7000 mysqlTo clone the 4.0 branch, use this command instead:
shell> bk clone bk://work.mysql.com:7001 mysql-4.0In the above examples the source tree will be set up in the `mysql/' or `mysql-4.0/' subdirectory of your current directory. The initial download of the source tree may take a while, depending on the speed of your connection; be patient.
autoconf 2.13, automake 1.4,
libtool, and m4 to run the next set of commands.
Note that the new versions of autoconf (2.52) and
automake (1.5) do not work. If you get some strange error during
this stage, check that you really have libtool installed! shell> cd mysql shell> bk -r edit shell> aclocal; autoheader; autoconf; automake; shell> ./configure # Add your favorite options here shell> makeA collection of our standard configure scripts is located in the `BUILD/' subdirectory. If you are lazy, you can use `BUILD/compile-pentium-debug'. To compile on a different architecture, modify the script removing flags that are Pentium-specific.
make install. Be careful with
this on a production machine; the command may overwrite your live release
installation. If you have another installation of MySQL, we recommand that you
run ./configure with different values for the
prefix, tcp-port, and unix-socket-path
options than those used for your production server.
make test. See section 9.1.2
MySQL Test Suite.
make stage and the distribution
does not compile, please report it to bugs@lists.mysql.com. If you have
installed the latest versions of the required GNU tools, and they crash trying
to process our configuration files, please report that also. However, if you
execute aclocal and get a command not found error or
a similar problem, do not report it. Instead, make sure all the necessary
tools are installed and that your PATH variable is set correctly
so your shell can find them.
bk clone operation to get the source tree,
you should run bk pull periodically to get the updates.
bk sccstool. If you see some funny diffs or code that you
have a question about, do not hesitate to send e-mail to internals@lists.mysql.com. Also,
if you think you have a better idea on how to do something, send an e-mail to
the same address with a patch. bk diffs will produce a patch for
you after you have made changes to the source. If you do not have the time to
code your idea, just send a description.
bk helptool. All MySQL programs compile cleanly for us with no warnings on Solaris using
gcc. On other systems, warnings may occur due to differences in
system include files. See section 2.3.6
MIT-pthreads Notes for warnings that may occur when using MIT-pthreads. For
other problems, check the list below.
The solution to many problems involves reconfiguring. If you do need to reconfigure, take note of the following:
configure is run after it already has been run, it may use
information that was gathered during its previous invocation. This information
is stored in `config.cache'. When configure starts up,
it looks for that file and reads its contents if it exists, on the assumption
that the information is still correct. That assumption is invalid when you
reconfigure.
configure, you must run make
again to recompile. However, you may want to remove old object files from
previous builds first, because they were compiled using different
configuration options. To prevent old configuration information or object files from being used, run
these commands before rerunning configure:
shell> rm config.cache shell> make clean
Alternatively, you can run make distclean.
The list below describes some of the problems compiling MySQL that have been found to occur most often:
Internal compiler error: program cc1plus got fatal signal 11 or Out of virtual memory or Virtual memory exhaustedThe problem is that
gcc requires huge amounts of memory to
compile `sql_yacc.cc' with inline functions. Try running
configure with the --with-low-memory option: shell> ./configure --with-low-memoryThis option causes
-fno-inline to be added to the compile
line if you are using gcc and -O0 if you are using
something else. You should try the --with-low-memory option even
if you have so much memory and swap space that you think you can't possibly
have run out. This problem has been observed to occur even on systems with
generous hardware configurations, and the --with-low-memory
option usually fixes it.
configure picks c++ as the compiler
name and GNU c++ links with -lg++. If you are using
gcc, that behavior can cause problems during configuration such
as this: configure: error: installation or configuration problem: C++ compiler cannot create executables.You might also observe problems during compilation related to
g++, libg++, or
libstdc++. One cause of these problems is that you may not have
g++, or you may have g++ but not
libg++, or libstdc++. Take a look at the
`config.log' file. It should contain the exact reason why your c++
compiler didn't work! To work around these problems, you can use
gcc as your C++ compiler. Try setting the environment variable
CXX to "gcc -O3". For example: shell> CXX="gcc -O3" ./configureThis works because
gcc compiles C++ sources as well as
g++ does, but does not link in libg++ or
libstdc++ by default. Another way to fix these problems, of
course, is to install g++, libg++ and
libstdc++.
make to GNU make: making all in mit-pthreads make: Fatal error in reader: Makefile, line 18: Badly formed macro assignment or make: file `Makefile' line 18: Must be a separator (: or pthread.h: No such file or directorySolaris and FreeBSD are known to have troublesome
make programs. GNU make Version 3.75 is known to
work.
CFLAGS and CXXFLAGS
environment variables. You can also specify the compiler names this way using
CC and CXX. For example: shell> CC=gcc shell> CFLAGS=-O3 shell> CXX=gcc shell> CXXFLAGS=-O3 shell> export CC CFLAGS CXX CXXFLAGSSee section 2.2.6 MySQL Binaries Compiled by MySQL AB, for a list of flag definitions that have been found to be useful on various systems.
gcc compiler: client/libmysql.c:273: parse error before `__attribute__'
gcc 2.8.1 is known to work, but we recommend using
gcc 2.95.2 or egcs 1.0.3a instead.
mysqld, configure didn't correctly detect the type
of the last argument to accept(), getsockname(), or
getpeername(): cxx: Error: mysqld.cc, line 645: In this statement, the referenced
type of the pointer value "&length" is "unsigned long", which
is not compatible with "int".
new_sock = accept(sock, (struct sockaddr *)&cAddr, &length);
To fix this, edit the `config.h' file (which is generated by
configure). Look for these lines: /* Define as the base type of the last arg to accept */ #define SOCKET_SIZE_TYPE XXXChange
XXX to size_t or int,
depending on your operating system. (Note that you will have to do this each
time you run configure, because configure
regenerates `config.h'.)
"sql_yacc.yy", line xxx fatal: default action causes potential...This is a sign that your version of
yacc is deficient. You
probably need to install bison (the GNU version of
yacc) and use that instead.
mysqld or a MySQL client, run
configure with the --with-debug option, then
recompile and link your clients with the new client library. See section E.2
Debugging a MySQL client. This section describes some of the issues involved in using MIT-pthreads.
Note that on Linux you should NOT use MIT-pthreads but install LinuxThreads! See section 2.6.1 Linux Notes (All Linux Versions).
If your system does not provide native thread support, you will need to build MySQL using the MIT-pthreads package. This includes older FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. See section 2.2.2 Operating Systems Supported by MySQL.
configure with the --with-mit-threads option: shell> ./configure --with-mit-threadsBuilding in a non-source directory is not supported when using MIT-pthreads, because we want to minimise our changes to this code.
--without-server to
build only the client code, clients will not know whether or not MIT-pthreads
is being used and will use Unix socket connections by default. Because Unix
sockets do not work under MIT-pthreads, this means you will need to use
-h or --host when you run client programs.
--use-locking option.
bind() command fails to bind to a
socket without any error message (at least on Solaris). The result is that all
connections to the server fail. For example: shell> mysqladmin version mysqladmin: connect to server at '' failed; error: 'Can't connect to mysql server on localhost (146)'The solution to this is to kill the
mysqld server and
restart it. This has only happened to us when we have forced the server down
and done a restart immediately.
sleep() system call isn't
interruptible with SIGINT (break). This is only noticeable when
you run mysqladmin --sleep. You must wait for the
sleep() call to terminate before the interrupt is served and the
process stops.
ld: warning: symbol `_iob' has differing sizes:
(file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
file /usr/lib/libc.so value=0x140);
/my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
ld: warning: symbol `__iob' has differing sizes:
(file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
file /usr/lib/libc.so value=0x140);
/my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
implicit declaration of function `int strtoll(...)' implicit declaration of function `int strtoul(...)'
readline to work with MIT-pthreads. (This
isn't needed, but may be interesting for someone.) You will need the following:
Building MySQL
File menu, select Open Workspace.
Build menu, select the Set Active
Configuration menu.
mysqld - Win32 Debug and
click OK.
F7 to begin the build of the debug server, libs and
some client applications.
Set up and start the server in the same way as for the binary Windows distribution. See section 2.1.2.2 Preparing the Windows MySQL Environment.
Once you've installed MySQL (from either a binary or source distribution), you need to initialise the grant tables, start the server, and make sure that the server works okay. You may also wish to arrange for the server to be started and stopped automatically when your system starts up and shuts down.
Normally you install the grant tables and start the server like this for installation from a source distribution:
shell> ./scripts/mysql_install_db shell> cd mysql_installation_directory shell> ./bin/safe_mysqld --user=mysql &
For a binary distribution (not RPM or pkg packages), do this:
shell> cd mysql_installation_directory shell> ./bin/mysql_install_db shell> ./bin/safe_mysqld --user=mysql &
This creates the mysql database which will hold all database
privileges, the test database which you can use to test MySQL and
also privilege entries for the user that run mysql_install_db and a
root user (without any passwords). This also starts the
mysqld server.
mysql_install_db will not overwrite any old privilege tables, so
it should be safe to run in any circumstances. If you don't want to have the
test database you can remove it with mysqladmin -u root drop
test.
Testing is most easily done from the top-level directory of the MySQL distribution. For a binary distribution, this is your installation directory (typically something like `/usr/local/mysql'). For a source distribution, this is the main directory of your MySQL source tree.
In the commands shown below in this section and in the following subsections,
BINDIR is the path to the location in which programs like
mysqladmin and safe_mysqld are installed. For a binary
distribution, this is the `bin' directory within the distribution. For
a source distribution, BINDIR is probably
`/usr/local/bin', unless you specified an installation directory other
than `/usr/local' when you ran configure.
EXECDIR is the location in which the mysqld server is
installed. For a binary distribution, this is the same as BINDIR.
For a source distribution, EXECDIR is probably
`/usr/local/libexec'.
Testing is described in detail below:
mysqld server and set up the initial
MySQL grant tables containing the privileges that determine how users are
allowed to connect to the server. This is normally done with the
mysql_install_db script: shell> scripts/mysql_install_dbTypically,
mysql_install_db needs to be run only the first
time you install MySQL. Therefore, if you are upgrading an existing
installation, you can skip this step. (However, mysql_install_db
is quite safe to use and will not update any tables that already exist, so if
you are unsure of what to do, you can always run
mysql_install_db.) mysql_install_db creates six
tables (user, db, host,
tables_priv, columns_priv, and func) in
the mysql database. A description of the initial privileges is
given in section 4.3.4
Setting Up the Initial MySQL Privileges. Briefly, these privileges allow
the MySQL root user to do anything, and allow anybody to create
or use databases with a name of 'test' or starting with
'test_'. If you don't set up the grant tables, the following
error will appear in the log file when you start the server: mysqld: Can't find file: 'host.frm'The above may also happen with a binary MySQL distribution if you don't start MySQL by executing exactly
./bin/safe_mysqld! See section
4.7.2
safe_mysqld, the wrapper around mysqld. You might need to run
mysql_install_db as root. However, if you prefer,
you can run the MySQL server as an unprivileged (non-root) user,
provided that user can read and write files in the database directory.
Instructions for running MySQL as an unprivileged user are given in section A.3.2
How to Run MySQL As a Normal User. If you have problems with
mysql_install_db, see section 2.4.1
Problems Running mysql_install_db. There are some
alternatives to running the mysql_install_db script as it is
provided in the MySQL distribution:
mysql_install_db before running it, to
change the initial privileges that are installed into the grant tables. This
is useful if you want to install MySQL on a lot of machines with the same
privileges. In this case you probably should need only to add a few extra
INSERT statements to the mysql.user and
mysql.db tables!
mysql_install_db, then use mysql -u root
mysql to connect to the grant tables as the MySQL root
user and issue SQL statements to modify the grant tables directly.
mysql_install_db. shell> cd mysql_installation_directory shell> bin/safe_mysqld &If you have problems starting the server, see section 2.4.2 Problems Starting the MySQL Server.
mysqladmin to verify that the server is running. The
following commands provide a simple test to check that the server is up and
responding to connections: shell> BINDIR/mysqladmin version shell> BINDIR/mysqladmin variablesThe output from
mysqladmin version varies slightly
depending on your platform and version of MySQL, but should be similar to that
shown below: shell> BINDIR/mysqladmin version mysqladmin Ver 8.14 Distrib 3.23.32, for linux on i586 Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB This software comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to modify and redistribute it under the GPL license Server version 3.23.32-debug Protocol version 10 Connection Localhost via Unix socket TCP port 3306 UNIX socket /tmp/mysql.sock Uptime: 16 sec Threads: 1 Questions: 9 Slow queries: 0 Opens: 7 Flush tables: 2 Open tables: 0 Queries per second avg: 0.000 Memory in use: 132K Max memory used: 16773KTo get a feeling for what else you can do with
BINDIR/mysqladmin, invoke it with the --help option.
shell> BINDIR/mysqladmin -u root shutdown
safe_mysqld or by invoking mysqld directly. For
example: shell> BINDIR/safe_mysqld --log &If
safe_mysqld fails, try running it from the MySQL
installation directory (if you are not already there). If that doesn't work,
see section 2.4.2
Problems Starting the MySQL Server.
shell> BINDIR/mysqlshow +-----------+ | Databases | +-----------+ | mysql | +-----------+ shell> BINDIR/mysqlshow mysql Database: mysql +--------------+ | Tables | +--------------+ | columns_priv | | db | | func | | host | | tables_priv | | user | +--------------+ shell> BINDIR/mysql -e "select host,db,user from db" mysql +------+--------+------+ | host | db | user | +------+--------+------+ | % | test | | | % | test_% | | +------+--------+------+There is also a benchmark suite in the `sql-bench' directory (under the MySQL installation directory) that you can use to compare how MySQL performs on different platforms. The `sql-bench/Results' directory contains the results from many runs against different databases and platforms. To run all tests, execute these commands:
shell> cd sql-bench shell> run-all-testsIf you don't have the `sql-bench' directory, you are probably using an RPM for a binary distribution. (Source distribution RPMs include the benchmark directory.) In this case, you must first install the benchmark suite before you can use it. Beginning with MySQL Version 3.22, there are benchmark RPM files named `mysql-bench-VERSION-i386.rpm' that contain benchmark code and data. If you have a source distribution, you can also run the tests in the `tests' subdirectory. For example, to run `auto_increment.tst', do this:
shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tstThe expected results are shown in the `./tests/auto_increment.res' file.
mysql_install_dbThe purpose of the mysql_install_db script is to generate new
MySQL privilege tables. It will not affect any other data! It will also not do
anything if you already have MySQL privilege tables installed!
If you want to re-create your privilege tables, you should take down the
mysqld server, if it's running, and then do something like:
mv mysql-data-directory/mysql mysql-data-directory/mysql-old mysql_install_db
This section lists problems you might encounter when you run
mysql_install_db:
mysql_install_db doesn't install the grant
tables
mysql_install_db fails to install the grant
tables and terminates after displaying the following messages: starting mysqld daemon with databases from XXXXXX mysql daemon endedIn this case, you should examine the log file very carefully! The log should be located in the directory `XXXXXX' named by the error message, and should indicate why
mysqld didn't start. If you
don't understand what happened, include the log when you post a bug report
using mysqlbug! See section 1.6.2.3
How to Report Bugs or Problems.
mysqld daemon running
mysql_install_db
at all. You have to run mysql_install_db only once, when you
install MySQL the first time.
mysqld daemon doesn't work when
one daemon is running
Can't start server: Bind on TCP/IP port:
Address already in use or Can't start server : Bind on unix
socket.... See section 4.1.3
Installing Many Servers on the Same Machine.
mysql_install_db or when starting or using
mysqld. You can specify a different socket and temporary
directory as follows: shell> TMPDIR=/some_tmp_dir/ shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock shell> export TMPDIR MYSQL_UNIX_PORTSee section A.4.5 How to Protect or change the MySQL socket file `/tmp/mysql.sock'. `some_tmp_dir' should be the path to some directory for which you have write permission. See section F Environment Variables. After this you should be able to run
mysql_install_db and start the server with these commands: shell> scripts/mysql_install_db shell> BINDIR/safe_mysqld &
mysqld crashes immediately
glibc
older than 2.0.7-5, you should make sure you have installed all
glibc patches! There is a lot of information about this in the
MySQL mail archives. Links to the mail archives are available online at http://lists.mysql.com/. Also, see section
2.6.1
Linux Notes (All Linux Versions). You can also start mysqld
manually using the --skip-grant-tables option and add the
privilege information yourself using mysql: shell> BINDIR/safe_mysqld --skip-grant-tables & shell> BINDIR/mysql -u root mysqlFrom
mysql, manually execute the SQL commands in
mysql_install_db. Make sure you run mysqladmin
flush-privileges or mysqladmin reload afterward to tell
the server to reload the grant tables. If you are going to use tables that support transactions (InnoDB, BDB), you should first create a my.cnf file and set startup options for the table types you plan to use. See section 7 MySQL Table Types.
Generally, you start the mysqld server in one of these ways:
mysql.server. This script is used primarily at
system startup and shutdown, and is described more fully in section 2.4.3
Starting and Stopping MySQL Automatically.
safe_mysqld, which tries to determine the proper
options for mysqld and then runs it with those options. See
section 4.7.2
safe_mysqld, the wrapper around mysqld.
mysqld directly. When the mysqld daemon starts up, it changes directory to the
data directory. This is where it expects to write log files and the pid (process
ID) file, and where it expects to find databases.
The data directory location is hardwired in when the distribution is
compiled. However, if mysqld expects to find the data directory
somewhere other than where it really is on your system, it will not work
properly. If you have problems with incorrect paths, you can find out what
options mysqld allows and what the default path settings are by
invoking mysqld with the --help option. You can
override the defaults by specifying the correct pathnames as command-line
arguments to mysqld. (These options can be used with
safe_mysqld as well.)
Normally you should need to tell mysqld only the base directory
under which MySQL is installed. You can do this with the --basedir
option. You can also use --help to check the effect of changing
path options (note that --help must be the final option of
the mysqld command). For example:
shell> EXECDIR/mysqld --basedir=/usr/local --help
Once you determine the path settings you want, start the server without the
--help option.
Whichever method you use to start the server, if it fails to start up
correctly, check the log file to see if you can find out why. Log files are
located in the data directory (typically `/usr/local/mysql/data' for a
binary distribution, `/usr/local/var' for a source distribution,
`\mysql\data\mysql.err' on Windows). Look in the data directory for
files with names of the form `host_name.err' and
`host_name.log' where host_name is the name of your server
host. Then check the last few lines of these files:
shell> tail host_name.err shell> tail host_name.log
If you find something like the following in the log file:
000729 14:50:10 bdb: Recovery function for LSN 1 27595 failed 000729 14:50:10 bdb: warning: ./test/t1.db: No such file or directory 000729 14:50:10 Can't init databases
This means that you didn't start mysqld with
--bdb-no-recover and Berkeley DB found something wrong with its log
files when it tried to recover your databases. To be able to continue, you
should move away the old Berkeley DB log file from the database directory to
some other place, where you can later examine these. The log files are named
`log.0000000001', where the number will increase over time.
If you are running mysqld with BDB table support and
mysqld core dumps at start this could be because of some problems
with the BDB recover log. In this case you can try starting mysqld
with --bdb-no-recover. If this helps, then you should remove all
`log.*' files from the data directory and try starting
mysqld again.
If you get the following error, it means that some other program (or another
mysqld server) is already using the TCP/IP port or socket
mysqld is trying to use:
Can't start server: Bind on TCP/IP port: Address already in use or Can't start server : Bind on unix socket...
Use ps to make sure that you don't have another
mysqld server running. If you can't find another server running,
you can try to execute the command telnet your-host-name
tcp-ip-port-number and press Enter a couple of times. If you don't get an
error message like telnet: Unable to connect to remote host: Connection
refused, something is using the TCP/IP port mysqld is trying
to use. See section 2.4.1
Problems Running mysql_install_db and section 4.1.4
Running Multiple MySQL Servers on the Same Machine.
If mysqld is currently running, you can find out what path
settings it is using by executing this command:
shell> mysqladmin variables
or
shell> mysqladmin -h 'your-host-name' variables
If you get Errcode 13, which means Permission
denied, when starting mysqld this means that you didn't have
the right to read/create files in the MySQL database or log directory. In this
case you should either start mysqld as the root user or change the
permissions for the involved files and directories so that you have the right to
use them.
If safe_mysqld starts the server but you can't connect to it,
you should make sure you have an entry in `/etc/hosts' that looks like
this:
127.0.0.1 localhost
This problem occurs only on systems that don't have a working thread library and for which MySQL must be configured to use MIT-pthreads.
If you can't get mysqld to start you can try to make a trace
file to find the problem. See section E.1.2
Creating trace files.
If you are using InnoDB tables, refer to the InnoDB-specific startup options. See section 7.5.2 InnoDB Startup Options.
If you are using BDB (Berkeley DB) tables, you should familiarise yourself with the different BDB specific startup options. See section 7.6.3 BDB startup options.
The mysql.server and safe_mysqld scripts can be
used to start the server automatically at system startup time.
mysql.server can also be used to stop the server.
The mysql.server script can be used to start or stop the server
by invoking it with start or stop arguments:
shell> mysql.server start shell> mysql.server stop
mysql.server can be found in the `share/mysql'
directory under the MySQL installation directory or in the
`support-files' directory of the MySQL source tree.
Before mysql.server starts the server, it changes directory to
the MySQL installation directory, then invokes safe_mysqld. You
might need to edit mysql.server if you have a binary distribution
that you've installed in a non-standard location. Modify it to cd
into the proper directory before it runs safe_mysqld. If you want
the server to run as some specific user, add an appropriate user
line to the `/etc/my.cnf' file, as shown later in this section.
mysql.server stop brings down the server by sending a signal to
it. You can take down the server manually by executing mysqladmin
shutdown.
You might want to add these start and stop commands to the appropriate places
in your `/etc/rc*' files when you start using MySQL for production
applications. Note that if you modify mysql.server, then upgrade
MySQL sometime, your modified version will be overwritten, so you should make a
copy of your edited version that you can reinstall.
If your system uses `/etc/rc.local' to start external scripts, you should append the following to it:
/bin/sh -c 'cd /usr/local/mysql ; ./bin/safe_mysqld --user=mysql &'
You can also add options for mysql.server in
a global `/etc/my.cnf' file. A typical `/etc/my.cnf' file
might look like this:
[mysqld] datadir=/usr/local/mysql/var socket=/var/tmp/mysql.sock port=3306 user=mysql [mysql.server] basedir=/usr/local/mysql
The mysql.server script understands the following options:
datadir, basedir, and pid-file.
The following table shows which option groups each of the startup scripts read from option files:
| Script | Option groups |
mysqld |
mysqld and server |
mysql.server |
mysql.server, mysqld, and
server |
safe_mysqld |
mysql.server, mysqld, and
server |
See section 4.1.2 my.cnf Option Files.
You can always move the MySQL form and data files between different versions
on the same architecture as long as you have the same base version of MySQL. The
current base version is 3. If you change the character set when running MySQL
(which may also change the sort order), you must run myisamchk -r
-q on all tables. Otherwise your indexes may not be ordered correctly.
If you are afraid of new versions, you can always rename your old
mysqld to something like mysqld-'old-version-number'.
If your new mysqld then does something unexpected, you can simply
shut it down and restart with your old mysqld!
When you do an upgrade you should also back up your old databases, of course.
If after an upgrade, you experience problems with recompiled client programs,
like Commands out of sync or unexpected core dumps, you probably
have used an old header or library file when compiling your programs. In this
case you should check the date for your `mysql.h' file and
`libmysqlclient.a' library to verify that they are from the new MySQL
distribution. If not, please recompile your programs!
If you get some problems that the new mysqld server doesn't want
to start or that you can't connect without a password, check that you don't have
some old `my.cnf' file from your old installation! You can check this
with: program-name --print-defaults. If this outputs anything other
than the program name, you have an active my.cnf file that will
affect things!
It is a good idea to rebuild and reinstall the
Msql-Mysql-modules distribution whenever you install a new release
of MySQL, particularly if you notice symptoms such as all your DBI
scripts dumping core after you upgrade MySQL.
You can use your old data files without any modification with Version 4.0. If
you want to move your data from a MySQL 4.0 server to an older server, you have
to use mysqldump.
Old clients should work with a Version 4.0 server without any problems.
The following lists tell what you have to watch out for when upgrading to version 4.0;
MATCH ... AGAINST (... IN BOOLEAN MODE) with your
tables, you need to rebuild them with ALTER TABLE table_name
TYPE=MyISAM, even if they are of MyISAM
type.
LOCATE() and INSTR() are case sensitive if
neither argument is a binary string.
HEX(string) now returns the characters in string converted to
hexadecimal. If you want to convert a number to hexadecimal, you should ensure
that you call HEX() with a numeric argument.
INSERT INTO ... SELECT always had
IGNORE enabled. In 4.0.1, MySQL will stop (and possibly roll
back) in case of an error if you don't specify IGNORE.
mysql_drop_db,
mysql_create_db and mysql_connect are not supported
anymore, unless you compile MySQL with
CFLAGS=-DUSE_OLD_FUNCTIONS. Instead of doing this, it is
preferable to change the client to use the new 4.0 API.
MYSQL_FIELD structure, length and
max_length has changed from unsigned int to
unsigned long. This should not cause any other problems than some
warnings if you use these to printf() type function.
TRUNCATE TABLE when you want to delete all
rows from a table and you don't care of how many rows where deleted. (Because
TRUNCATE TABLE is faster than DELETE FROM
table_name).
LOCK TABLES or
transaction when trying to execute TRUNCATE TABLE or DROP
DATABASE.
SHOW OPEN TABLE has changed.
mysql_thread_init() and
mysql_thread_end(). See section 8.4.8
How to Make a Threaded Client.
drop_db() call.
RAND(seed) returns a different random number series in 4.0
than in 3.23; This was done to get RAND(seed) and
RAND(seed+1) more different. MySQL Version 3.23 supports tables of the new MyISAM type and
the old ISAM type. You don't have to convert your old tables to use
these with Version 3.23. By default, all new tables will be created with type
MyISAM (unless you start mysqld with the
--default-table-type=isam option). You can change an
ISAM table to a MyISAM table with ALTER TABLE
table_name TYPE=MyISAM or the Perl script
mysql_convert_table_format.
Version 3.22 and 3.21 clients will work without any problems with a Version 3.23 server.
The following lists tell what you have to watch out for when upgrading to Version 3.23:
tis620 character set must be fixed
with myisamchk -r or REPAIR TABLE.
DROP DATABASE on a symbolic linked database, both
the link and the original database is deleted. (This didn't happen in 3.22
because configure didn't detect the readlink system call).
OPTIMIZE TABLE now only works for MyISAM
tables. For other table types, you can use ALTER TABLE to
optimise the table. During OPTIMIZE TABLE the table is now locked
from other threads.
mysql is now by default started with the
option --no-named-commands (-g). This option can be disabled with
--enable-named-commands (-G). This may cause incompatibility
problems in some cases, for example in SQL scripts that use named commands
without a semicolon! Long format commands still work from the first line.
MONTH()) will
now return 0 for 0000-00-00 dates. (MySQL 3.22 returned
NULL).
german character sort order, you must
repair all your tables with isamchk -r, as we have made some
changes in the sort order!
IF will now depend on both
arguments and not only the first argument.
AUTO_INCREMENT will not work with negative numbers. The
reason for this is that negative numbers caused problems when wrapping from -1
to 0. AUTO_INCREMENT is now for MyISAM tables handled at a lower
level and is much faster than before. For MyISAM tables old numbers are also
not reused anymore, even if you delete some rows from the table.
CASE, DELAYED, ELSE,
END, FULLTEXT, INNER,
RIGHT, THEN and WHEN are now reserved
words.
FLOAT(X) is now a true floating-point type and not a value
with a fixed number of decimals.
DECIMAL(length,dec) the length argument no
longer includes a place for the sign or the decimal point.
TIME string must now be of one of the following formats:
[[[DAYS] [H]H:]MM:]SS[.fraction] or
[[[[[H]H]H]H]MM]SS[.fraction]
LIKE now compares strings using the same character comparison
rules as '='. If you require the old behavior, you can compile
MySQL with the CXXFLAGS=-DLIKE_CMP_TOUPPER flag.
REGEXP is now case insensitive for normal (not binary)
strings.
CHECK TABLE or
myisamchk for MyISAM tables (.MYI) and
isamchk for ISAM (.ISM) tables.
mysqldump files to be compatible between
MySQL Version 3.22 and Version 3.23, you should not use the --opt
or --full option to mysqldump.
DATE_FORMAT() to make sure there is a
`%' before each format character. (Later MySQL Version 3.22 did
allow this syntax.)
mysql_fetch_fields_direct is now a function (it was a macro)
and it returns a pointer to a MYSQL_FIELD instead of a
MYSQL_FIELD.
mysql_num_fields() can no longer be used on a
MYSQL* object (it's now a function that takes
MYSQL_RES* as an argument. You should now use
mysql_field_count() instead.
SELECT DISTINCT ... was
almost always sorted. In Version 3.23, you must use GROUP BY or
ORDER BY to obtain sorted output.
SUM() now returns NULL, instead of 0, if there
is no matching rows. This is according to ANSI SQL.
AND or OR with NULL values will
now return NULL instead of 0. This mostly affects queries that
use NOT on an AND/OR expression as NOT
NULL = NULL. LPAD() and RPAD()
will shorten the result string if it's longer than the length argument.
Nothing that affects compatibility has changed between Version 3.21 and 3.22.
The only pitfall is that new tables that are created with DATE type
columns will use the new way to store the date. You can't access these new
fields from an old version of mysqld.
After installing MySQL Version 3.22, you should start the new server and then
run the mysql_fix_privilege_tables script. This will add the new
privileges that you need to use the GRANT command. If you forget
this, you will get Access denied when you try to use ALTER
TABLE, CREATE INDEX, or DROP INDEX. If your
MySQL root user requires a password, you should give this as an argument to
mysql_fix_privilege_tables.
The C API interface to mysql_real_connect() has changed. If you
have an old client program that calls this function, you must place a
0 for the new db argument (or recode the client to
send the db element for faster connections). You must also call
mysql_init() before calling mysql_real_connect()! This
change was done to allow the new mysql_options() function to save
options in the MYSQL handler structure.
The mysqld variable key_buffer has changed names to
key_buffer_size, but you can still use the old name in your startup
files.
If you are running a version older than Version 3.20.28 and want to switch to Version 3.21, you need to do the following:
You can start the mysqld Version 3.21 server with
safe_mysqld --old-protocol to use it with clients from a Version
3.20 distribution. In this case, the new client function
mysql_errno() will not return any server error, only
CR_UNKNOWN_ERROR (but it works for client errors), and the server
uses the old password() checking rather than the new one.
If you are not using the --old-protocol option
to mysqld, you will need to make the following changes:
scripts/add_long_password must be run to convert
the Password field in the mysql.user table to
CHAR(16).
mysql.user table (to
get 62-bit rather than 31-bit passwords).
MySQL Version 3.20.28 and above can handle the new user table
format without affecting clients. If you have a MySQL version earlier than
Version 3.20.28, passwords will no longer work with it if you convert the
user table. So to be safe, you should first upgrade to at least
Version 3.20.28 and then upgrade to Version 3.21.
The new client code works with a 3.20.x
mysqld server, so if you experience problems with 3.21.x, you can
use the old 3.20.x server without having to recompile the clients again.
If you are not using the --old-protocol option to
mysqld, old clients will issue the error message:
ERROR: Protocol mismatch. Server Version = 10 Client Version = 9
The new Perl DBI/DBD interface also supports the
old mysqlperl interface. The only change you have to make if you
use mysqlperl is to change the arguments to the
connect() function. The new arguments are: host,
database, user, password (the
user and password arguments have changed places). See
section 8.2.2
The DBI Interface.
The following changes may affect queries in old applications:
HAVING must now be specified before any ORDER BY
clause.
LOCATE() have been swapped.
DATE,
TIME, and TIMESTAMP. If you are using MySQL Version 3.23, you can copy the .frm,
.MYI, and .MYD files between different architectures
that support the same floating-point format. (MySQL takes care of any byte
swapping issues.)
The MySQL ISAM data and index files (`.ISD' and
`*.ISM', respectively) are architecture-dependent and in some cases
OS-dependent. If you want to move your applications to another machine that has
a different architecture or OS than your current machine, you should not try to
move a database by simply copying the files to the other machine. Use
mysqldump instead.
By default, mysqldump will create a file full of SQL statements.
You can then transfer the file to the other machine and feed it as input to the
mysql client.
Try mysqldump --help to see what options are available. If you
are moving the data to a newer version of MySQL, you should use mysqldump
--opt with the newer version to get a fast, compact dump.
The easiest (although not the fastest) way to move a database between two machines is to run the following commands on the machine on which the database is located:
shell> mysqladmin -h 'other hostname' create db_name
shell> mysqldump --opt db_name \
| mysql -h 'other hostname' db_name
If you want to copy a database from a remote machine over a slow network, you can use:
shell> mysqladmin create db_name
shell> mysqldump -h 'other hostname' --opt --compress db_name \
| mysql db_name
You can also store the result in a file, then transfer the file to the target machine and load the file into the database there. For example, you can dump a database to a file on the source machine like this:
shell> mysqldump --quick db_name | gzip > db_name.contents.gz
(The file created in this example is compressed.) Transfer the file containing the database contents to the target machine and run these commands there:
shell> mysqladmin create db_name shell> gunzip < db_name.contents.gz | mysql db_name
You can also use mysqldump
and mysqlimport to accomplish the database transfer. For big
tables, this is much faster than simply using mysqldump. In the
commands shown below, DUMPDIR represents the full pathname of the
directory you use to store the output from mysqldump.
First, create the directory for the output files and dump the database:
shell> mkdir DUMPDIR shell> mysqldump --tab=DUMPDIR db_name
Then transfer the files in the DUMPDIR directory to some
corresponding directory on the target machine and load the files into MySQL
there:
shell> mysqladmin create db_name # create database shell> cat DUMPDIR/*.sql | mysql db_name # create tables in database shell> mysqlimport db_name DUMPDIR/*.txt # load data into tables
Also, don't forget to copy the mysql database, because that's
where the grant tables (user, db, host)
are stored. You may have to run commands as the MySQL root user on
the new machine until you have the mysql database in place.
After you import the mysql database on the new machine, execute
mysqladmin flush-privileges so that the server reloads the grant
table information.
The notes below regarding glibc apply only to the situation when you build MySQL yourself. If you are running Linux on an x86 machine, in most cases it is much better for you to just use our binary. We link our binaries against the best patched version of glibc we can come up with and with the best compiler options, in an attempt to make it suitable for a high-load server. So if you read the text below, and are in doubt about what you should do, try our binary first to see if it meets your needs, and worry about your own build only after you have discovered that our binary is not good enough. In that case, we would appreciate a note about it, so we can build a better binary next time. For a typical user, even for setups with a lot of concurrent connections and/or tables exceeding 2GB limit, our binary in most cases is the best choice.
MySQL uses LinuxThreads on Linux. If you are using an old Linux version that
doesn't have glibc2, you must install LinuxThreads before trying to
compile MySQL. You can get LinuxThreads at http://mysql.com/Downloads/Linux/.
Note: We have seen some strange problems with Linux 2.2.14 and MySQL on SMP systems; If you have a SMP system, we recommend you to upgrade to Linux 2.4 as soon as possible! Your system will be faster and more stable by doing this!
Note that glibc versions before and including Version 2.1.1 have
a fatal bug in pthread_mutex_timedwait handling, which is used when
you do INSERT DELAYED. We recommend you to not use INSERT
DELAYED before upgrading glibc.
If you plan to have 1000+ concurrent connections, you will need to make some
changes to LinuxThreads, recompile it, and relink MySQL against the new
`libpthread.a'. Increase PTHREAD_THREADS_MAX in
`sysdeps/unix/sysv/linux/bits/local_lim.h' to 4096 and decrease
STACK_SIZE in `linuxthreads/internals.h' to 256 KB. The
paths are relative to the root of glibc Note that MySQL will not be
stable with around 600-1000 connections if STACK_SIZE is the
default of 2 MB.
If you have a problem with that MySQL can't open enough files, or connections, it may be that you haven't configured Linux to handle enough files.
In Linux 2.2 and forwards, you can check the number of allocated file handlers by doing:
cat /proc/sys/fs/file-max cat /proc/sys/fs/dquot-max cat /proc/sys/fs/super-max
If you have more than 16M of memory, you should add something like the following in your boot script (`/etc/rc/boot.local' on SuSE):
echo 65536 > /proc/sys/fs/file-max echo 8192 > /proc/sys/fs/dquot-max echo 1024 > /proc/sys/fs/super-max
You can also run the above from the command line as root, but in this case your old limits will be used next time your computer reboots.
You should also add /etc/my.cnf:
[safe_mysqld] open-files-limit=8192
The above should allow MySQL to create up to 8192 connections + files.
The STACK_SIZE constant in LinuxThreads controls the spacing of
thread stacks in the address space. It needs to be large enough so that there
will be plenty of room for the stack of each individual thread, but small enough
to keep the stack of some thread from running into the global
mysqld data. Unfortunately, the Linux implementation of
mmap(), as we have experimentally discovered, will successfully
unmap an already mapped region if you ask it to map out an address already in
use, zeroing out the data on the entire page, instead of returning an error. So,
the safety of mysqld or any other threaded application depends on
the "gentleman" behavior of the code that creates threads. The user must take
measures to make sure the number of running threads at any time is sufficiently
low for thread stacks to stay away from the global heap. With
mysqld, you should enforce this "gentleman" behavior by setting a
reasonable value for the max_connections variable.
If you build MySQL yourself and do not want to mess with patching
LinuxThreads, you should set max_connections to a value no higher
than 500. It should be even less if you have a large key buffer, large heap
tables, or some other things that make mysqld allocate a lot of
memory or if you are running a 2.2 kernel with a 2GB patch. If you are using our
binary or RPM version 3.23.25 or later, you can safely set
max_connections at 1500, assuming no large key buffer or heap
tables with lots of data. The more you reduce STACK_SIZE in
LinuxThreads the more threads you can safely create. We recommend the values
between 128K and 256K.
If you use a lot of concurrent connections, you may suffer from a "feature"
in the 2.2 kernel that penalises a process for forking or cloning a child in an
attempt to prevent a fork bomb attack. This will cause MySQL not to scale well
as you increase the number of concurrent clients. On single CPU systems, we have
seen this manifested in a very slow thread creation, which means it may take a
long time to connect to MySQL (as long as 1 minute), and it may take just as
long to shut it down. On multiple CPU systems, we have observed a gradual drop
in query speed as the number of clients increases. In the process of trying to
find a solution, we have received a kernel patch from one of our users, who
claimed it made a lot of difference for his site. The patch is available here
(http://mysql.com/Downloads/Patches/linux-fork.patch).
We have now done rather extensive testing of this patch on both development and
production systems. It has significantly improved MySQL performance
without causing any problems and we now recommend it to our users who are still
running high-load servers on 2.2 kernels. This issue has been fixed in the 2.4
kernel, so if you are not satisfied with the current performance of your system,
rather than patching your 2.2 kernel, it might be easier to just upgrade to 2.4,
which will also give you a nice SMP boost in addition to fixing this fairness
bug.
We have tested MySQL on the 2.4 kernel on a 2 CPU machine and found MySQL
scales MUCH better - there was virtually no slowdown on query throughput all the
way up to 1000 clients, and MySQL scaling factor ( computed as the ratio of
maximum throughput to the throughput with one client) was 180%. We have observed
similar results on a 4-CPU system - virtually no slowdown as the number of
clients was increased up to 1000, and 300% scaling factor. So for a high-load
SMP server we would definitely recommend the 2.4 kernel at this point. We have
discovered that it is essential to run mysqld process with the
highest possible priority on the 2.4 kernel to achieve maximum performance. This
can be done by adding renice -20 $$ command to
safe_mysqld. In our testing on a 4-CPU machine, increasing the
priority gave 60% increase in throughput with 400 clients.
We are currently also trying to collect more info on how well
MySQL performs on 2.4 kernel on 4-way and 8-way systems. If you
have access such a system and have done some benchmarks, please send a mail to
docs@mysql.com with the results - we will
include them in the manual.
There is another issue that greatly hurts MySQL performance, especially on SMP systems. The implementation of mutex in LinuxThreads in glibc-2.1 is very bad for programs with many threads that only hold the mutex for a short time. On an SMP system, ironic as it is, if you link MySQL against unmodified LinuxThreads, removing processors from the machine improves MySQL performance in many cases. We have made a patch available for glibc 2.1.3 to correct this behavior (http://mysql.com/Downloads/Linux/linuxthreads-2.1-patch).
With glibc-2.2.2 MySQL version 3.23.36 will use the adaptive
mutex, which is much better than even the patched one in
glibc-2.1.3. Be warned, however, that under some conditions,
the current mutex code in glibc-2.2.2 overspins, which hurts
MySQL performance. The chance of this condition can be reduced by renicing
mysqld process to the highest priority. We have also been able to
correct the overspin behavior with a patch, available at http://mysql.com/Downloads/Linux/linuxthreads-2.2.2.patch.
It combines the correction of overspin, maximum number of threads, and stack
spacing all in one. You will need to apply it in the linuxthreads
directory with patch -p0 </tmp/linuxthreads-2.2.2.patch. We hope
it will be included in some form in to the future releases of
glibc-2.2. In any case, if you link against
glibc-2.2.2 you still need to correct STACK_SIZE and
PTHREAD_THREADS_MAX. We hope that the defaults will be corrected to
some more acceptable values for high-load MySQL setup in the future, so that
your own build can be reduced to ./configure; make; make install.
We recommend that you use the above patches to build a special static version
of libpthread.a and use it only for statically linking against
MySQL. We know that the patches are safe for MySQL and
significantly improve its performance, but we cannot say anything about other
applications. If you link other applications against the patched version of the
library, or build a patched shared version and install it on your system, you
are doing it at your own risk with regard to other applications that depend on
LinuxThreads.
If you experience any strange problems during the installation of MySQL, or with some common utilties hanging, it is very likely that they are either library or compiler related. If this is the case, using our binary will resolve them.
One known problem with the binary distribution is that with older Linux
systems that use libc (like RedHat 4.x or Slackware), you will get
some non-fatal problems with hostname resolution. See section 2.6.1.1
Linux Notes for Binary Distributions.
When using LinuxThreads you will see a minimum of three processes running. These are in fact threads. There will be one thread for the LinuxThreads manager, one thread to handle connections, and one thread to handle alarms and signals.
Note that the Linux kernel and the LinuxThread library can by default only have 1024 threads. This means that you can only have up to 1021 connections to MySQL on an unpatched system. The page http://www.volano.com/linuxnotes.html contains information how to go around this limit.
If you see a dead mysqld daemon process with ps,
this usually means that you have found a bug in MySQL or you have a corrupted
table. See section A.4.1 What
To Do If MySQL Keeps Crashing.
To get a core dump on Linux if mysqld dies with a SIGSEGV
signal, you can start mysqld with the --core-file
option. Note that you also probably need to raise the core file
size by adding ulimit -c 1000000 to safe_mysqld
or starting safe_mysqld with
--core-file-sizes=1000000. See section 4.7.2
safe_mysqld, the wrapper around mysqld.
If you are linking your own MySQL client and get the error:
ld.so.1: ./my: fatal: libmysqlclient.so.4: open failed: No such file or directory
When executing them, the problem can be avoided by one of the following methods:
-Lpath):
-Wl,r/path-libmysqlclient.so.
libmysqclient.so to `/usr/lib'.
libmysqlclient.so is
located to the LD_RUN_PATH environment variable before running
your client. If you are using the Fujitsu compiler (fcc / FCC) you will have
some problems compiling MySQL because the Linux header files are very
gcc oriented.
The following configure line should work with
fcc/FCC:
CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE -DCONST=const -DNO_STRTOLL_PROTO" CXX=FCC CXXFLAGS="-O -K fast -K lib -K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE -DCONST=const -Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO '-D_EXTERN_INLINE=static __inline'" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-low-memory
MySQL needs at least Linux Version 2.0.
WARNING: We have have reports from some MySQL users that they have got serious stability problems with MySQL with Linux kernel 2.2.14. If you are using this kernel you should upgrade to 2.2.19 (or newer) or to a 2.4 kernel. If you have a multi-cpu box, then you should seriously consider using 2.4 as this will give you a significant speed boost.
The binary release is linked with -static, which means you do
not normally need to worry about which version of the system libraries you have.
You need not install LinuxThreads, either. A program linked with
-static is slightly bigger than a dynamically linked program but
also slightly faster (3-5%). One problem, however, is that you can't use
user-definable functions (UDFs) with a statically linked program. If you are
going to write or use UDF functions (this is something only for C or C++
programmers), you must compile MySQL yourself, using dynamic linking.
If you are using a libc-based system (instead of a
glibc2 system), you will probably get some problems with hostname
resolving and getpwnam() with the binary release. (This is because
glibc unfortunately depends on some external libraries to resolve
hostnames and getpwent(), even when compiled with
-static). In this case you probably get the following error message
when you run mysql_install_db:
Sorry, the host 'xxxx' could not be looked up
or the following error when you try to run mysqld with the
--user option:
getpwnam: No such file or directory
You can solve this problem in one of the following ways:
tar.gz
distribution) and install this instead.
mysql_install_db --force; This will not execute the
resolveip test in mysql_install_db. The downside is
that you can't use host names in the grant tables; you must use IP numbers
instead (except for localhost). If you are using an old MySQL
release that doesn't support --force, you have to remove the
resolveip test in mysql_install with an editor.
mysqld with su instead of using
--user. The Linux-Intel binary and RPM releases of MySQL are configured for the highest possible speed. We are always trying to use the fastest stable compiler available.
MySQL Perl support requires Version Perl 5.004_03 or newer.
On some Linux 2.2 versions, you may get the error Resource temporarily
unavailable when you do a lot of new connections to a mysqld
server over TCP/IP.
The problem is that Linux has a delay between when you close a TCP/IP socket and until this is actually freed by the system. As there is only room for a finite number of TCP/IP slots, you will get the above error if you try to do too many new TCP/IP connections during a small time, like when you run the MySQL `test-connect' benchmark over TCP/IP.
We have mailed about this problem a couple of times to different Linux mailing lists but have never been able to resolve this properly.
The only known 'fix' to this problem is to use persistent connections in your
clients or use sockets, if you are running the database server and clients on
the same machine. We hope that the Linux 2.4 kernel will fix this
problem in the future.
MySQL requires libc Version 5.4.12 or newer. It's known to work
with libc 5.4.46. glibc Version 2.0.6 and later should
also work. There have been some problems with the glibc RPMs from
RedHat, so if you have problems, check whether or not there are any updates! The
glibc 2.0.7-19 and 2.0.7-29 RPMs are known to work.
If you are using gcc 3.0 and above to compile MySQL, you must install the
libstdc++v3 library before compiling MySQL; If you don't do this
you will get an error about a missing __cxa_pure_virtual symbol
during linking!
On some older Linux distributions, configure may produce an
error like this:
Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file. See the Installation chapter in the Reference Manual.
Just do what the error message says and add an extra underscore to the
_P macro that has only one underscore, then try again.
You may get some warnings when compiling; those shown below can be ignored:
mysqld.cc -o objs-thread/mysqld.o mysqld.cc: In function `void init_signals()': mysqld.cc:315: warning: assignment of negative value `-1' to `long unsigned int' mysqld.cc: In function `void * signal_hand(void *)': mysqld.cc:346: warning: assignment of negative value `-1' to `long unsigned int'
In Debian GNU/Linux, if you want MySQL to start automatically when the system boots, do the following:
shell> cp support-files/mysql.server /etc/init.d/mysql.server shell> /usr/sbin/update-rc.d mysql.server defaults 99
mysql.server can be found in the `share/mysql'
directory under the MySQL installation directory or in the
`support-files' directory of the MySQL source tree.
If mysqld always core dumps when it starts up, the problem may
be that you have an old `/lib/libc.a'. Try renaming it, then remove
`sql/mysqld' and do a new make install and try again. This
problem has been reported on some Slackware installations.
If you get the following error when linking mysqld, it means
that your `libg++.a' is not installed correctly:
/usr/lib/libc.a(putc.o): In function `_IO_putc': putc.o(.text+0x0): multiple definition of `_IO_putc'
You can avoid using `libg++.a' by running configure
like this:
shell> CXX=gcc ./configure
If you are running gcc 3.0 and above, you can't use the above trick with setting to CXX=gcc.
In some implementations, readdir_r() is broken. The symptom is
that SHOW DATABASES always returns an empty set. This can be fixed
by removing HAVE_READDIR_R from `config.h' after
configuring and before compiling.
Some problems will require patching your Linux installation. The patch can be
found at http://mysql.com/Downloads/patches/Linux-sparc-2.0.30.diff.
This patch is against the Linux distribution `sparclinux-2.0.30.tar.gz'
that is available at vger.rutgers.edu (a version of Linux that was
never merged with the official 2.0.30). You must also install LinuxThreads
Version 0.6 or newer.
MySQL Version 3.23.12 is the first MySQL version that is tested on Linux-Alpha. If you plan to use MySQL on Linux-Alpha, you should ensure that you have this version or newer.
We have tested MySQL on Alpha with our benchmarks and test suite, and it appears to work nicely. The main thing we haven't yet had time to test is how things works with many concurrent users.
When we compiled the standard MySQL binary we are using SuSE 6.4, kernel 2.2.13-SMP, Compaq C compiler (V6.2-504) and Compaq C++ compiler (V6.3-005) on a Comaq DS20 machine with an Alpha EV6 processor.
You can find the above compilers at http://www.support.compaq.com/alpha-tools/). By using these compilers, instead of gcc, we get about 9-14 % better performance with MySQL.
Note that the configure line optimised the binary for the current CPU; This means you can only use our binary if you have an Alpha EV6 processor. We also compile statically to avoid library problems.
CC=ccc CFLAGS="-fast" CXX=cxx CXXFLAGS="-fast -noexceptions -nortti" ./configure --prefix=/usr/local/mysql --disable-shared --with-extra-charsets=complex --enable-thread-safe-client --with-mysqld-ldflags=-non_shared --with-client-ldflags=-non_shared
If you want to use egcs the following configure line worked for us:
CFLAGS="-O3 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --disable-shared
Some known problems when running MySQL on Linux-Alpha:
gdb
4.18. You should download and use gdb 5.1 instead!
mysqld statically when using
gcc, the resulting image will core dump at start. In other words,
don't use --with-mysqld-ldflags=-all-static with
gcc. MySQL should work on MkLinux with the newest glibc package
(tested with glibc 2.0.7).
To get MySQL to work on Qube2, (Linux Mips), you need the newest
glibc libraries (glibc-2.0.7-29C2 is known to work).
You must also use the egcs C++ compiler (egcs-1.0.2-9,
gcc 2.95.2 or newer).
To get MySQL to compile on Linux Ia64, we use the following compile line:
Using gcc-2.96:
CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql "--with-comment=Official MySQL binary" --with-extra-charsets=complex
On Ia64 the MySQL client binaries are using shared libraries. This means that
if you install our binary distribution in some other place than
`/usr/local/mysql' you need to either modify `/etc/ld.so.conf'
or add the path to the directory where you have `libmysqlclient.so' to
the LD_LIBRARY_PATH environment variable.
See section A.3.1 Problems When Linking with the MySQL Client Library.
This section describes using MySQL on Windows. This information is also provided in the `README' file that comes with the MySQL Windows distribution. See section 2.1.2 Installing MySQL on Windows.
MySQL uses TCP/IP to connect a client to a server. (This will allow any machine on your network to connect to your MySQL server.) Because of this, you must install TCP/IP on your machine before starting MySQL. You can find TCP/IP on your Windows CD-ROM.
Note that if you are using an old Win95 release (for example OSR2), it's likely that you have an old Winsock package; MySQL requires Winsock 2! You can get the newest Winsock from http://www.microsoft.com/. Win98 has the new Winsock 2 library, so the above doesn't apply for Win98.
To start the mysqld server, you should start an MS-DOS window
and type:
C:\> C:\mysql\bin\mysqld
This will start mysqld in the background without a window.
You can kill the MySQL server by executing:
C:\> C:\mysql\bin\mysqladmin -u root shutdown
This calls the MySQL administation utility as user `root', which is the default Administrator in the MySQL grant system. Please note that the MySQL grant system is wholly independent from any login users under Windows.
Note that Win95 and Win98 don't support creation of named pipes. On Win95 and
Win98, you can only use named pipes to connect to a remote MySQL server running
on a Windows NT/2000 server host. (The MySQL server must also support named
pipes, of course. For example, using mysqld-opt under NT/2000 will
not allow named pipe connections. You should use either mysqld-nt
or mysqld-max-nt.)
If mysqld doesn't start, please check the
`\mysql\data\mysql.err' file to see if the server wrote any message
there to indicate the cause of the problem. You can also try to start the server
with mysqld --standalone; In this case, you may get some useful
information on the screen that may help solve the problem.
The last option is to start mysqld with --standalone
--debug. In this case mysqld will write a log file
`C:\mysqld.trace' that should contain the reason why
mysqld doesn't start. See section E.1.2
Creating trace files.
Use mysqld --help to display all the options that
mysqld understands!
To get MySQL to work with TCP/IP on Windows NT 4, you must install service pack 3 (or newer)!
Normally you should install MySQL as a service on NT/Win2000. In case the server was already running, first stop it using the following command:
C:\mysql\bin> mysqladmin -u root shutdown
This calls the MySQL administation utility as user `root', which
is the default Administrator in the MySQL grant system. Please note
that the MySQL grant system is wholly independent from any login users under
Windows.
Now install the server service:
C:\mysql\bin> mysqld-max-nt --install
If any options are required, they must be specified as ``Start
parameters'' in the Windows Services utility before you
start the MySQL service.
The Services utility (Windows Service Control
Manager) can be found in the Windows Control Panel (under
Administrative Tools on Windows 2000). It is advisable to close the
Services utility while performing the --install or
--remove operations, this prevents some odd errors.
For information about which server binary to run, see section 2.1.2.2 Preparing the Windows MySQL Environment.
Please note that from MySQL version 3.23.44, you have the choice of set up
the service as Manual instead (if you don't wish the service to be
started automatically during the boot process):
C:\mysql\bin> mysqld-max-nt --install-manual
The service is installed with the name MySQL. Once installed, it
can be immediately started from the Services utility, or by using
the command NET START MySQL.
Once running, mysqld-max-nt can be stopped using
mysqladmin, from the Services utility or by using the command
NET STOP MySQL.
Please note that when run as a service, mysqld-max-nt has no
access to a console and so no messages can be seen. Errors can be checked in
`c:\mysql\data\mysql.err'.
If you have problems installing mysqld-max-nt as a service, try
starting it with the full path:
C:\> C:\mysql\bin\mysqld-max-nt --install
If this doesn't work, you can get mysqld-max-nt to start
properly by fixing the path in the registry!
If you don't want to start mysqld-max-nt as a service, you can
start it as follows:
C:\> C:\mysql\bin\mysqld-max-nt --standalone
or
C:\> C:\mysql\bin\mysqld --standalone --debug
The last method gives you a debug trace in `C:\mysqld.trace'. See section E.1.2 Creating trace files.
MySQL supports TCP/IP on all Windows platforms and named pipes on NT/2000. The default is to use named pipes for local connections on NT/2000 and TCP/IP for all other cases if the client has TCP/IP installed. The host name specifies which protocol is used:
| Host name | Protocol |
| NULL (none) | On NT/2000, try named pipes first; if that doesn't work, use TCP/IP. On Win95/Win98, TCP/IP is used. |
| . | Named pipes |
| localhost | TCP/IP to current host |
| hostname | TCP/IP |
You can force a MySQL client to use named pipes by specifying the
--pipe option or by specifying . as the host name. Use
the --socket option to specify the name of the pipe.
You can test whether or not MySQL is working by executing the following commands:
C:\> C:\mysql\bin\mysqlshow C:\> C:\mysql\bin\mysqlshow -u root mysql C:\> C:\mysql\bin\mysqladmin version status proc C:\> C:\mysql\bin\mysql test
If mysqld is slow to answer to connections on Win95/Win98, there
is probably a problem with your DNS. In this case, start mysqld
with --skip-name-resolve and use only localhost and IP
numbers in the MySQL grant tables. You can also avoid DNS when connecting to a
mysqld-nt MySQL server running on NT by using the
--pipe argument to specify use of named pipes. This works for most
MySQL clients.
There are two versions of the MySQL command-line tool:
| Binary | Description |
mysql |
Compiled on native Windows, which offers very limited text editing capabilities. |
mysqlc |
Compiled with the Cygnus GNU compiler and libraries, which offers
readline editing. |
If you want to use mysqlc.exe, you must copy
`C:\mysql\lib\cygwinb19.dll' to your Windows system directory
(`\windows\system' or similar place).
The default privileges on Windows give all local users full privileges to all
databases without specifying a password. To make MySQL more secure, you should
set a password for all users and remove the row in the mysql.user
table that has Host='localhost' and User=''.
You should also add a password for the root user. The following
example starts by removing the anonymous user that can be used by anyone to
access the test database, then sets a root user
password:
C:\> C:\mysql\bin\mysql mysql mysql> DELETE FROM user WHERE Host='localhost' AND User=''; mysql> QUIT C:\> C:\mysql\bin\mysqladmin reload C:\> C:\mysql\bin\mysqladmin -u root password your_password
After you've set the password, if you want to take down the
mysqld server, you can do so using this command:
C:\> mysqladmin --user=root --password=your_password shutdown
If you are using the old shareware version of MySQL Version 3.21 under
Windows, the above command will fail with an error: parse error near 'SET
OPTION password'. The fix is in to upgrade to the current MySQL version,
which is freely available.
With the current MySQL versions you can easily add new users and change
privileges with GRANT and REVOKE commands. See section
4.3.1
GRANT and REVOKE Syntax.
Here is a note about how to connect to get a secure connection to remote MySQL server with SSH (by David Carlson dcarlson@mplcomm.com):
SecureCRT from http://www.vandyke.com/. Another option is
f-secure from http://www.f-secure.com/. You can also
find some free ones on Google at http://directory.google.com/Top/Computers/Security/Products_and_Tools/Cryptography/SSH/Clients/Windows/.
Host_Name =
yourmysqlserver_URL_or_IP. Set userid=your_userid to log
in to your server (probably not the same as your MySQL login/password.
local_port:
3306, remote_host: yourmysqlservername_or_ip,
remote_port: 3306 ) or a local forward (Set port:
3306, host: localhost, remote port: 3306).
localhost for the MySQL
host server -- not yourmysqlservername. You should now have an ODBC connection to MySQL, encrypted using SSH.
Beginning with MySQL Version 3.23.16, the mysqld-max and
mysql-max-nt servers in the MySQL distribution are compiled with
the -DUSE_SYMDIR option. This allows you to put a database on
different disk by adding a symbolic link to it (in a manner similar to the way
that symbolic links work on Unix).
On Windows, you make a symbolic link to a database by creating a file that contains the path to the destination directory and saving this in the `mysql_data' directory under the filename `database.sym'. Note that the symbolic link will be used only if the directory `mysql_data_dir\database' doesn't exist.
For example, if the MySQL data directory is `C:\mysql\data' and you
want to have database foo located at `D:\data\foo', you
should create the file `C:\mysql\data\foo.sym' that contains the text
D:\data\foo\. After that, all tables created in the database
foo will be created in `D:\data\foo'.
Note that because of the speed penalty you get when opening every table, we
have not enabled this by default even if you have compiled MySQL with support
for this. To enable symlinks you should put in your my.cnf or
my.ini file the following entry:
[mysqld] use-symbolic-links
In MySQL 4.0 we will enable symlinks by default. Then you should instead use
the skip-symlink option if you want to disable this.
In your source files, you should include `windows.h' before you include `mysql.h':
#if defined(_WIN32) || defined(_WIN64) #include <windows.h> #endif #include <mysql.h>
You can either link your code with the dynamic `libmysql.lib' library, which is just a wrapper to load in `libmysql.dll' on demand, or link with the static `mysqlclient.lib' library.
Note that as the mysqlclient libraries are compiled as threaded libraries, you should also compile your code to be multi-threaded!
MySQL-Windows has by now proven itself to be very stable. This version of MySQL has the same features as the corresponding Unix version with the following exceptions:
mysqld for an extended time on Win95 if your server handles many
connections! WinNT and Win98 don't suffer from this bug.
pread() and pwrite() calls
to be able to mix INSERT and SELECT. Currently we
use mutexes to emulate pread()/pwrite(). We will, in
the long run, replace the file level interface with a virtual interface so
that we can use the readfile()/writefile() interface
on NT to get more speed. The current implementation limits the number of open
files MySQL can use to 1024, which means that you will not be able to run as
many concurrent threads on NT as on Unix.
mysqladmin kill will not work on a sleeping connection.
mysqladmin shutdown can't abort as long as there are
sleeping connections. DROP DATABASE
mysqladmin shutdown.
LOAD DATA INFILE or SELECT ... INTO OUTFILE, you
must double the `\' character: mysql> LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr; mysql> SELECT * INTO OUTFILE 'C:\\tmp\\skr.txt' FROM skr;Alternatively, use Unix style filenames with `/' characters:
mysql> LOAD DATA INFILE "C:/tmp/skr.txt" INTO TABLE skr; mysql> SELECT * INTO OUTFILE 'C:/tmp/skr.txt' FROM skr;
Can't open named pipe error
error 2017: can't open named pipe to host: . pipe...This is because the release version of MySQL uses named pipes on NT by default. You can avoid this error by using the
--host=localhost option to the new MySQL clients or create an
option file `C:\my.cnf' that contains the following information: [client] host = localhost
Access denied for user error
Access denied for user: 'some-user@unknown' to
database 'mysql' when accessing a MySQL server on the same machine,
this means that MySQL can't resolve your host name properly. To fix this, you
should create a file `\windows\hosts' with the following information:
127.0.0.1 localhost
ALTER TABLE
ALTER TABLE statement, the table
is locked from usage by other threads. This has to do with the fact that on
Windows, you can't delete a file that is in use by another threads. (In the
future, we may find some way to work around this problem.)
DROP TABLE on a table that is in use by a MERGE
table will not work on Windows because MERGE handler does the
table mapping hidden from the upper layer of MySQL. Because Windows doesn't
allow you to drop files that are open, you first must flush all
MERGE tables (with FLUSH TABLES) or drop the
MERGE table before dropping the table. We will fix this at the
same time we introduce VIEWs.
DATA DIRECTORY and INDEX DIRECTORY directives in
CREATE TABLE is ignored on Windows, because Windows doesn't
support symbolic links. Here are some open issues for anyone who might want to help us with the Windows release:
MYSQL.DLL server. This should include
everything in a standard MySQL server, except thread creation. This will make
MySQL much easier to use in applications that don't need a true client/server
and don't need to access the server from other hosts.
mysqld as a service with
--install (on NT) it would be nice if you could also add default
options on the command line. For the moment, the workaround is to list the
parameters in the `C:\my.cnf' file instead.
mysqld from the task
manager. For the moment, you must use mysqladmin shutdown.
readline to Windows for use in the mysql
command line tool.
mysql,
mysqlshow, mysqladmin, and mysqldump)
would be nice.
mysqladmin kill on Windows.
mysqld always starts in the "C" locale and not in the default
locale. We would like to have mysqld use the current locale for
the sort order.
.DLLs.
Other Windows-specific issues are described in the `README' file that comes with the MySQL-Windows distribution.
On Solaris, you may run into trouble even before you get the MySQL
distribution unpacked! Solaris tar can't handle long file names, so
you may see an error like this when you unpack MySQL:
x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks tar: directory checksum error
In this case, you must use GNU tar (gtar) to unpack
the distribution. You can find a precompiled copy for Solaris at http://mysql.com/Downloads/.
Sun native threads work only on Solaris 2.5 and higher. For Version 2.4 and earlier, MySQL will automatically use MIT-pthreads. See section 2.3.6 MIT-pthreads Notes.
If you get the following error from configure:
checking for restartable system calls... configure: error can not run test programs while cross compiling
This means that you have something wrong with your compiler installation! In this case you should upgrade your compiler to a newer version. You may also be able to solve this problem by inserting the following row into the `config.cache' file:
ac_cv_sys_restartable_syscalls=${ac_cv_sys_restartable_syscalls='no'}
If you are using Solaris on a SPARC, the recommended compiler is
gcc 2.95.2. You can find this at http://gcc.gnu.org/. Note that egcs
1.1.1 and gcc 2.8.1 don't work reliably on SPARC!
The recommended configure line when using gcc
2.95.2 is:
CC=gcc CFLAGS="-O3" \ CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory --enable-assembler
If you have a ultra sparc, you can get 4 % more performance by adding "-mcpu=v8 -Wa,-xarch=v8plusa" to CFLAGS and CXXFLAGS.
If you have Sun Workshop (Fortre) 5.3 (or newer) compiler, you can run
configure like this:
CC=cc CFLAGS="-Xa -fast -xO4 -native -xstrconst -mt" \ CXX=CC CXXFLAGS="-noex -xO4 -mt" \ ./configure --prefix=/usr/local/mysql --enable-assembler
In the MySQL benchmarks, we got a 6 % speedup on an Ultrasparc when using Sun Workshop 5.3 compared to using gcc with -mcpu flags.
If you get a problem with fdatasync or sched_yield,
you can fix this by adding LIBS=-lrt to the configure line
The following paragraph is only relevant for older compilers than WorkShop 5.3:
You may also have to edit the configure script to change this
line:
#if !defined(__STDC__) || __STDC__ != 1
to this:
#if !defined(__STDC__)
If you turn on __STDC__ with the -Xc option, the
Sun compiler can't compile with the Solaris `pthread.h' header file.
This is a Sun bug (broken compiler or broken include file).
If mysqld issues the error message shown below when you run it,
you have tried to compile MySQL with the Sun compiler without enabling the
multi-thread option (-mt):
libc internal error: _rmutex_unlock: rmutex not held
Add -mt to CFLAGS and CXXFLAGS and try
again.
If you are using the SFW version of gcc (which comes with Solaris 8), you
must add `/opt/sfw/lib' to the environment variable
LD_LIBRARY_PATH before running configure. If you are using the gcc
available from sunfreeware.com, you may have many problems. You
should recompile gcc and GNU binutils on the machine you will be running them
from to avoid any problems.
If you get the following error when compiling MySQL with gcc, it
means that your gcc is not configured for your version of Solaris:
shell> gcc -O3 -g -O2 -DDBUG_OFF -o thr_alarm ... ./thr_alarm.c: In function `signal_hand': ./thr_alarm.c:556: too many arguments to function `sigwait'
The proper thing to do in this case is to get the newest version of
gcc and compile it with your current gcc compiler! At
least for Solaris 2.5, almost all binary versions of gcc have old,
unusable include files that will break all programs that use threads (and
possibly other programs)!
Solaris doesn't provide static versions of all system libraries
(libpthreads and libdl), so you can't compile MySQL
with --static. If you try to do so, you will get the error:
ld: fatal: library -ldl: not found or undefined reference to `dlopen' or cannot find -lrt
If too many processes try to connect very rapidly to mysqld, you
will see this error in the MySQL log:
Error in accept: Protocol error
You might try starting the server with the --set-variable
back_log=50 option as a workaround for this. See section 4.1.1
mysqld Command-line Options.
If you are linking your own MySQL client, you might get the following error when you try to execute it:
ld.so.1: ./my: fatal: libmysqlclient.so.#: open failed: No such file or directory
The problem can be avoided by one of the following methods:
-Lpath):
-Wl,r/full-path-to-libmysqlclient.so.
LD_RUN_PATH environment variable before running
your client. If you have problems with configure trying to link with -lz and
you don't have zlib installed, you have two options:
--with-named-z-libs=no. If you are using gcc and have problems with loading UDF
functions into MySQL, try adding -lgcc to the link line for the
UDF function.
If you would like MySQL to start automatically, you can copy `support-files/mysql.server' to `/etc/init.d' and create a symbolic link to it named `/etc/rc3.d/S99mysql.server'.
You can normally use a Solaris 2.6 binary on Solaris 2.7 and 2.8. Most of the Solaris 2.6 issues also apply for Solaris 2.7 and 2.8.
Note that MySQL Version 3.23.4 and above should be able to autodetect new versions of Solaris and enable workarounds for the following problems!
Solaris 2.7 / 2.8 has some bugs in the include files. You may see the
following error when you use gcc:
/usr/include/widec.h:42: warning: `getwc' redefined /usr/include/wchar.h:326: warning: this is the location of the previous definition
If this occurs, you can do the following to fix the problem:
Copy /usr/include/widec.h to
.../lib/gcc-lib/os/gcc-version/include and change line 41 from:
#if !defined(lint) && !defined(__lint) to #if !defined(lint) && !defined(__lint) && !defined(getwc)
Alternatively, you can edit `/usr/include/widec.h' directly. Either
way, after you make the fix, you should remove `config.cache' and run
configure again!
If you get errors like this when you run make, it's because
configure didn't detect the `curses.h' file (probably
because of the error in `/usr/include/widec.h'):
In file included from mysql.cc:50: /usr/include/term.h:1060: syntax error before `,' /usr/include/term.h:1081: syntax error before `;'
The solution to this is to do one of the following:
CFLAGS=-DHAVE_CURSES_H CXXFLAGS=-DHAVE_CURSES_H
./configure.
#define HAVE_TERM line from `config.h'
file and run make again. If you get a problem that your linker can't find -lz when
linking your client program, the problem is probably that your
`libz.so' file is installed in `/usr/local/lib'. You can fix
this by one of the following methods:
LD_LIBRARY_PATH.
--with-named-z-libs=no option.
On Solaris 2.8 on x86, mysqld will core dump if you run 'strip'
in.
If you are using gcc or egcs on Solaris x86 and you
experience problems with core dumps under load, you should use the following
configure command:
CC=gcc CFLAGS="-O3 -fomit-frame-pointer -DHAVE_CURSES_H" \ CXX=gcc \ CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti -DHAVE_CURSES_H" \ ./configure --prefix=/usr/local/mysql
This will avoid problems with the libstdc++ library and with C++
exceptions.
If this doesn't help, you should compile a debug version and run it with a
trace file or under gdb. See section E.1.3
Debugging mysqld under gdb.
This section provides information for the various BSD flavours, as well as specific versions within those.
FreeBSD 3.x is recommended for running MySQL since the thread package is much more integrated.
The easiest and therefor the preferred way to install is to use the mysql-server and mysql-client ports available on http://www.freebsd.org/.
Using these gives you:
It is recommended you use MIT-pthreads on FreeBSD 2.x and native threads on
Versions 3 and up. It is possible to run with native threads on some late 2.2.x
versions but you may encounter problems shutting down mysqld.
The MySQL `Makefile's require GNU make (gmake) to work.
If you want to compile MySQL you need to install GNU make first.
Be sure to have your name resolver setup correct. Otherwise you may
experience resolver delays or failures when connecting to mysqld.
Make sure that the localhost entry in the `/etc/hosts'
file is correct (otherwise you will have problems connecting to the database).
The `/etc/hosts' file should start with a line:
127.0.0.1 localhost localhost.your.domain
The recommended way to compile and install MySQL on FreeBSD with gcc (2.95.2 and up) is:
CC=gcc CFLAGS="-O2 -fno-strength-reduce" \ CXX=gcc CXXFLAGS="-O2 -fno-rtti -fno-exceptions -felide-constructors -fno-strength-reduce" \ ./configure --prefix=/usr/local/mysql --enable-assembler gmake gmake install ./scripts/mysql_install_db cd /usr/local/mysql ./bin/mysqld_safe &
If you notice that configure will use MIT-pthreads, you should
read the MIT-pthreads notes. See section 2.3.6
MIT-pthreads Notes.
If you get an error from make install that it can't find
`/usr/include/pthreads', configure didn't detect that you
need MIT-pthreads. This is fixed by executing these commands:
shell> rm config.cache shell> ./configure --with-mit-threads
FreeBSD is also known to have a very low default file handle limit. See
section A.2.16
File Not Found. Uncomment the ulimit -n section in safe_mysqld or raise the
limits for the mysqld user in /etc/login.conf (and rebuild it with
cap_mkdb /etc/login.conf). Also be sure you set the appropriate class for this
user in the password file if you are not using the default (use: chpass
mysqld-user-name). See section 4.7.2
safe_mysqld, the wrapper around mysqld.
If you have a lot of memory you should consider rebuilding the kernel to
allow MySQL to take more than 512M of RAM. Take a look at option
MAXDSIZ in the LINT config file for more info.
If you get problems with the current date in MySQL, setting the
TZ variable will probably help. See section F
Environment Variables.
To get a secure and stable system you should only use FreeBSD kernels that
are marked -RELEASE.
To compile on NetBSD you need GNU make. Otherwise the compile
will crash when make tries to run lint on C++ files.
On OpenBSD Version 2.5, you can compile MySQL with native threads with the following options:
CFLAGS=-pthread CXXFLAGS=-pthread ./configure --with-mit-threads=no
Our users have reported that OpenBSD 2.8 has a threading bug which causes problems with MySQL. The OpenBSD Developers have fixed the problem, but as of January 25th, 2001, it's only available in the ``-current'' branch. The symptoms of this threading bug are: slow response, high load, high CPU usage, and crashes.
If you get the following error when compiling MySQL, your ulimit
value for virtual memory is too low:
item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)': item_func.h:28: virtual memory exhausted make[2]: *** [item_func.o] Error 1
Try using ulimit -v 80000 and run make again. If
this doesn't work and you are using bash, try switching to
csh or sh; some BSDI users have reported problems with
bash and ulimit.
If you are using gcc, you may also use have to use the
--with-low-memory flag for configure to be able to
compile `sql_yacc.cc'.
If you get problems with the current date in MySQL, setting the
TZ variable will probably help. See section F
Environment Variables.
Upgrade to BSD/OS Version 3.1. If that is not possible, install BSDIpatch M300-038.
Use the following command when configuring MySQL:
shell> env CXX=shlicc++ CC=shlicc2 \
./configure \
--prefix=/usr/local/mysql \
--localstatedir=/var/mysql \
--without-perl \
--with-unix-socket-path=/var/mysql/mysql.sock
The following is also known to work:
shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \
./configure \
--prefix=/usr/local/mysql \
--with-unix-socket-path=/var/mysql/mysql.sock
You can change the directory locations if you wish, or just use the defaults by not specifying any locations.
If you have problems with performance under heavy load, try using the
--skip-thread-priority option to mysqld! This will run
all threads with the same priority; on BSDI Version 3.1, this gives better
performance (at least until BSDI fixes their thread scheduler).
If you get the error virtual memory exhausted while compiling,
you should try using ulimit -v 80000 and run make
again. If this doesn't work and you are using bash, try switching
to csh or sh; some BSDI users have reported problems
with bash and ulimit.
BSDI Version 4.x has some thread-related bugs. If you want to use MySQL on this, you should install all thread-related patches. At least M400-023 should be installed.
On some BSDI Version 4.x systems, you may get problems with shared libraries.
The symptom is that you can't execute any client programs, for example,
mysqladmin. In this case you need to reconfigure not to use shared
libraries with the --disable-shared option to configure.
Some customers have had problems on BSDI 4.0.1 that the mysqld
binary after a while can't open tables. This is because some library/system
related bug causes mysqld to change current directory without
asking for this!
The fix is to either upgrade to 3.23.34 or after running
configure remove the line #define HAVE_REALPATH from
config.h before running make.
Note that the above means that you can't symbolic link a database directories to another database directory or symbolic link a table to another database on BSDI! (Making a symbolic link to another disk is okay).
MySQL should work without any problems on Mac OS X Public Beta (Darwin). You don't need the pthread patches for this OS!
Before trying to configure MySQL on Mac OS X server you must first install the pthread package from http://www.prnet.de/RegEx/mysql.html.
Our binary for Mac OS X is compiled on Rhapsody 5.5 with the following configure line:
CC=gcc CFLAGS="-O2 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O2 -fomit-frame-pointer" ./configure --prefix=/usr/local/mysql "--with-comment=Official MySQL binary" --with-extra-charsets=complex --disable-shared
You might want to also add aliases to your shell's resource file to access
mysql and mysqladmin from the command line:
alias mysql '/usr/local/mysql/bin/mysql' alias mysqladmin '/usr/local/mysql/bin/mysqladmin'
Some of the binary distributions of MySQL for HP-UX is distributed as an HP depot file and as a tar file. To use the depot file you must be running at least HP-UX 10.x to have access to HP's software depot tools.
The HP version of MySQL was compiled on an HP 9000/8xx server under HP-UX 10.20, and uses MIT-pthreads. It is known to work well under this configuration. MySQL Version 3.22.26 and newer can also be built with HP's native thread package.
Other configurations that may work:
The following configurations almost definitely won't work:
To install the distribution, use one of the commands below, where
/path/to/depot is the full pathname of the depot file:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.full
shell> /usr/sbin/swinstall -s /path/to/depot mysql.server
shell> /usr/sbin/swinstall -s /path/to/depot mysql.client
shell> /usr/sbin/swinstall -s /path/to/depot mysql.developer
The depot places binaries and libraries in `/opt/mysql' and data in
`/var/opt/mysql'. The depot also creates the appropriate entries in
`/etc/init.d' and `/etc/rc2.d' to start the server
automatically at boot time. Obviously, this entails being root to
install.
To install the HP-UX tar.gz distribution, you must have a copy of GNU
tar.
There are a couple of small problems when compiling MySQL on HP-UX. We
recommend that you use gcc instead of the HP-UX native compiler,
because gcc produces better code!
We recommend using gcc 2.95 on HP-UX. Don't use high optimisation flags (like -O6) as this may not be safe on HP-UX.
Note that MIT-pthreads can't be compiled with the HP-UX compiler because it
can't compile .S (assembler) files.
The following configure line should work:
CFLAGS="-DHPUX -I/opt/dce/include -fpic" CXXFLAGS="-DHPUX -I/opt/dce/include -felide-constructors -fno-exceptions -fno-rtti" CXX=gcc ./configure --with-pthread --with-named-thread-libs='-ldce' --prefix=/usr/local/mysql --disable-shared
If you are compiling gcc 2.95 yourself, you should NOT link it
with the DCE libraries (libdce.a or libcma.a) if you
want to compile MySQL with MIT-pthreads. If you mix the DCE and MIT-pthreads
packages you will get a mysqld to which you cannot connect. Remove
the DCE libraries while you compile gcc 2.95!
For HP-UX Version 11.x we recommend MySQL Version 3.23.15 or later.
Because of some critical bugs in the standard HP-UX libraries, you should install the following patches before trying to run MySQL on HP-UX 11.0:
PHKL_22840 Streams cumulative PHNE_22397 ARPA cumulative
This will solve a problem that one gets EWOULDBLOCK from
recv() and EBADF from accept() in
threaded applications.
If you are using gcc 2.95.1 on an unpatched HP-UX 11.x system,
you will get the error:
In file included from /usr/include/unistd.h:11,
from ../include/global.h:125,
from mysql_priv.h:15,
from item.cc:19:
/usr/include/sys/unistd.h:184: declaration of C function ...
/usr/include/sys/pthread.h:440: previous declaration ...
In file included from item.h:306,
from mysql_priv.h:158,
from item.cc:19:
The problem is that HP-UX doesn't define pthreads_atfork()
consistently. It has conflicting prototypes in
`/usr/include/sys/unistd.h':184 and
`/usr/include/sys/pthread.h':440 (details below).
One solution is to copy `/usr/include/sys/unistd.h' into `mysql/include' and edit `unistd.h' and change it to match the definition in `pthread.h'. Here's the diff:
183,184c183,184 < extern int pthread_atfork(void (*prepare)(), void (*parent)(), < void (*child)()); --- > extern int pthread_atfork(void (*prepare)(void), void (*parent)(void), > void (*child)(void));
After this, the following configure line should work:
CFLAGS="-fomit-frame-pointer -O3 -fpic" CXX=gcc CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -O3" ./configure --prefix=/usr/local/mysql --disable-shared
Here is some information that a HP-UX Version 11.x user sent us about compiling MySQL with HP-UX:x compiler:
Environment:
proper compilers.
setenv CC cc
setenv CXX aCC
flags
setenv CFLAGS -D_REENTRANT
setenv CXXFLAGS -D_REENTRANT
setenv CPPFLAGS -D_REENTRANT
% aCC -V
aCC: HP ANSI C++ B3910B X.03.14.06
% cc -V /tmp/empty.c
cpp.ansi: HP92453-01 A.11.02.00 HP C Preprocessor (ANSI)
ccom: HP92453-01 A.11.01.00 HP C Compiler
cc: "/tmp/empty.c", line 1: warning 501: Empty source file.
configuration:
./configure --with-pthread \
--prefix=/source-control/mysql \
--with-named-thread-libs=-lpthread \
--with-low-memory
added '#define _CTYPE_INCLUDED' to include/m_ctype.h. This
symbol is the one defined in HP's /usr/include/ctype.h:
/* Don't include std ctype.h when this is included */
#define _CTYPE_H
#define __CTYPE_INCLUDED
#define _CTYPE_INCLUDED
#define _CTYPE_USING /* Don't put names in global namespace. */
-D_REENTRANT to get the
compiler to recognise the prototype for localtime_r.
Alternatively I could have supplied the prototype for
localtime_r. But I wanted to catch other bugs without needing to
run into them. I wasn't sure where I needed it, so I added it to all flags.
If you get the following error from configure
checking for cc option to accept ANSI C... no configure: error: MySQL requires a ANSI C compiler (and a C++ compiler). Try gcc. See the Installation chapter in the Reference Manual.
Check that you don't have the path to the K&R compiler before the path to the HP-UX C and C++ compiler.
Automatic detection of xlC is missing from Autoconf, so a
configure command something like this is needed when compiling
MySQL (This example uses the IBM compiler):
export CC="xlc_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192 " export CXX="xlC_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192" export CFLAGS="-I /usr/local/include" export LDLFAGS="-L /usr/local/lib" export CPPFLAGS=$CFLAGS export CXXFLAGS=$CFLAGS ./configure --prefix=/usr/local \ --localstatedir=/var/mysql \ --sysconfdir=/etc/mysql \ --sbindir='/usr/local/bin' \ --libexecdir='/usr/local/bin' \ --enable-thread-safe-client \ --enable-large-files
Above are the options used to compile the MySQL distribution that can be found at http://www-frec.bull.com/.
If you change the -O3 to -O2 in the above configure
line, you must also remove the -qstrict option (this is a
limitation in the IBM C compiler).
If you are using gcc or egcs to compile MySQL, you
must use the -fno-exceptions flag, as the
exception handling in gcc/egcs is not thread safe!
(This is tested with egcs 1.1.) There are also some known problems
with IBM's assembler, which may cause it to generate bad code when used with
gcc.
We recommend the following configure line with egcs
and gcc 2.95 on AIX:
CC="gcc -pipe -mcpu=power -Wa,-many" \ CXX="gcc -pipe -mcpu=power -Wa,-many" \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory
The -Wa,-many is necessary for the compile to be successful. IBM
is aware of this problem but is in to hurry to fix it because of the workaround
available. We don't know if the -fno-exceptions is required with
gcc 2.95, but as MySQL doesn't use exceptions and the above option
generates faster code, we recommend that you should always use this option with
egcs / gcc.
If you get a problem with assembler code try changing the -mcpu=xxx to match your cpu. Typically power2, power, or powerpc may need to be used, alternatively you might need to use 604 or 604e. I'm not positive but I would think using "power" would likely be safe most of the time, even on a power2 machine.
If you don't know what your cpu is then do a "uname -m", this will give you back a string that looks like "000514676700", with a format of xxyyyyyymmss where xx and ss are always 0's, yyyyyy is a unique system id and mm is the id of the CPU Planar. A chart of these values can be found at http://www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds5/uname.htm. This will give you a machine type and a machine model you can use to determine what type of cpu you have.
If you have problems with signals (MySQL dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \
CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -DDONT_USE_THR_ALARM" \
./configure --prefix=/usr/local/mysql --with-debug --with-low-memory
This doesn't affect the performance of MySQL, but has the side effect that
you can't kill clients that are ``sleeping'' on a connection with
mysqladmin kill or mysqladmin shutdown. Instead, the
client will die when it issues its next command.
On some versions of AIX, linking with libbind.a makes
getservbyname core dump. This is an AIX bug and should be reported
to IBM.
For AIX 4.2.1 and gcc you have to do the following changes.
After configuring, edit `config.h' and `include/my_config.h' and change the line that says
#define HAVE_SNPRINTF 1
to
#undef HAVE_SNPRINTF
And finally, in `mysqld.cc' you need to add a prototype for initgoups.
#ifdef _AIX41 extern "C" int initgroups(const char *,int); #endif
On SunOS 4, MIT-pthreads is needed to compile MySQL, which in turn means you
will need GNU make.
Some SunOS 4 systems have problems with dynamic libraries and
libtool. You can use the following configure line to
avoid this problem:
shell> ./configure --disable-shared --with-mysqld-ldflags=-all-static
When compiling readline, you may get warnings about duplicate
defines. These may be ignored.
When compiling mysqld, there will be some implicit
declaration of function warnings. These may be ignored.
If you are using egcs 1.1.2 on Digital Unix, you should upgrade to gcc 2.95.2, as egcs on DEC has some serious bugs!
When compiling threaded programs under Digital Unix, the documentation
recommends using the -pthread option for cc and
cxx and the libraries -lmach -lexc (in addition to
-lpthread). You should run configure something like
this:
CC="cc -pthread" CXX="cxx -pthread -O" \ ./configure --with-named-thread-libs="-lpthread -lmach -lexc -lc"
When compiling mysqld, you may see a couple of warnings like
this:
mysqld.cc: In function void handle_connections()': mysqld.cc:626: passing long unsigned int *' as argument 3 of accept(int,sockadddr *, int *)'
You can safely ignore these warnings. They occur because
configure can detect only errors, not warnings.
If you start the server directly from the command line, you may have problems
with it dying when you log out. (When you log out, your outstanding processes
receive a SIGHUP signal.) If so, try starting the server like this:
shell> nohup mysqld [options] &
nohup causes the command following it to ignore any
SIGHUP signal sent from the terminal. Alternatively, start the
server by running safe_mysqld, which invokes mysqld
using nohup for you. See section 4.7.2
safe_mysqld, the wrapper around mysqld.
If you get a problem when compiling mysys/get_opt.c, just remove the line #define _NO_PROTO from the start of that file!
If you are using Compac's CC compiler, the following configure line should work:
CC="cc -pthread" CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all -arch host" CXX="cxx -pthread" CXXFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all -arch host -noexceptions -nortti" export CC CFLAGS CXX CXXFLAGS ./configure \ --prefix=/usr/local/mysql \ --with-low-memory \ --enable-large-files \ --enable-shared=yes \ --with-named-thread-libs="-lpthread -lmach -lexc -lc" gnumake
If you get a problem with libtool, when compiling with shared libraries as
above, when linking mysql, you should be able to get around this by
issuing:
cd mysql /bin/sh ../libtool --mode=link cxx -pthread -O3 -DDBUG_OFF \ -O4 -ansi_alias -ansi_args -fast -inline speed \ -speculate all \ -arch host -DUNDEF_HAVE_GETHOSTBYNAME_R \ -o mysql mysql.o readline.o sql_string.o completion_hash.o \ ../readline/libreadline.a -lcurses \ ../libmysql/.libs/libmysqlclient.so -lm cd .. gnumake gnumake install scripts/mysql_install_db
If you have problems compiling and have DEC CC and
gcc installed, try running configure like this:
CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql
If you get problems with the `c_asm.h' file, you can create and use a 'dummy' `c_asm.h' file with:
touch include/c_asm.h CC=gcc CFLAGS=-I./include \ CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql
Note that the following problems with the ld program can be
fixed by downloading the latest DEC (Compaq) patch kit from: http://ftp.support.compaq.com/public/unix/.
On OSF1 V4.0D and compiler "DEC C V5.6-071 on Digital Unix V4.0 (Rev. 878)"
the compiler had some strange behavior (undefined asm symbols).
/bin/ld also appears to be broken (problems with _exit
undefined errors occuring while linking mysqld). On this
system, we have managed to compile MySQL with the following
configure line, after replacing /bin/ld with the
version from OSF 4.0C:
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
With the Digital compiler "C++ V6.1-029", the following should work:
CC=cc -pthread CFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host CXX=cxx -pthread CXXFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host -noexceptions -nortti export CC CFLAGS CXX CXXFLAGS ./configure --prefix=/usr/mysql/mysql --with-mysqld-ldflags=-all-static --disable-shared --with-named-thread-libs="-lmach -lexc -lc"
In some versions of OSF1, the alloca() function is broken. Fix
this by removing the line in `config.h' that defines
'HAVE_ALLOCA'.
The alloca() function also may have an incorrect prototype in
/usr/include/alloca.h. This warning resulting from this can be
ignored.
configure will use the following thread libraries automatically:
--with-named-thread-libs="-lpthread -lmach -lexc -lc".
When using gcc, you can also try running configure
like this:
shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure ....
If you have problems with signals (MySQL dies unexpectedly under high load), you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM \
CXXFLAGS=-DDONT_USE_THR_ALARM \
./configure ...
This doesn't affect the performance of MySQL, but has the side effect that
you can't kill clients that are ``sleeping'' on a connection with
mysqladmin kill or mysqladmin shutdown. Instead, the
client will die when it issues its next command.
With gcc 2.95.2, you will probably run into the following
compile error:
sql_acl.cc:1456: Internal compiler error in `scan_region', at except.c:2566 Please submit a full bug report.
To fix this you should change to the sql directory and do a
``cut and paste'' of the last gcc line, but change -O3
to -O0 (or add -O0 immediately after gcc
if you don't have any -O option on your compile line). After this
is done you can just change back to the top-level directly and run
make again.
If you are using Irix Version 6.5.3 or newer mysqld will only be
able to create threads if you run it as a user with CAP_SCHED_MGT
privileges (like root) or give the mysqld server this
privilege with the following shell command:
shell> chcap "CAP_SCHED_MGT+epi" /opt/mysql/libexec/mysqld
You may have to undefine some things in `config.h' after running
configure and before compiling.
In some Irix implementations, the alloca() function is broken.
If the mysqld server dies on some SELECT statements,
remove the lines from `config.h' that define HAVE_ALLOC
and HAVE_ALLOCA_H. If mysqladmin create doesn't work,
remove the line from `config.h' that defines
HAVE_READDIR_R. You may have to remove the HAVE_TERM_H
line as well.
SGI recommends that you install all of the patches on this page as a set: http://support.sgi.com/surfzone/patches/patchset/6.2_indigo.rps.html
At the very minimum, you should install the latest kernel rollup, the latest
rld rollup, and the latest libc rollup.
You definitely need all the POSIX patches on this page, for pthreads support:
http://support.sgi.com/surfzone/patches/patchset/6.2_posix.rps.html
If you get the something like the following error when compiling `mysql.cc':
"/usr/include/curses.h", line 82: error(1084): invalid combination of type
Type the following in the top-level directory of your MySQL source tree:
shell> extra/replace bool curses_bool < /usr/include/curses.h > include/curses.h shell> make
There have also been reports of scheduling problems. If only one thread is running, things go slow. Avoid this by starting another client. This may lead to a 2-to-10-fold increase in execution speed thereafter for the other thread. This is a poorly understood problem with Irix threads; you may have to improvise to find solutions until this can be fixed.
If you are compiling with gcc, you can use the following
configure command:
CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql --enable-thread-safe-client --with-named-thread-libs=-lpthread
On Irix 6.5.11 with native Irix C and C++ compilers ver. 7.3.1.2, the following is reported to work
CC=cc CXX=CC CFLAGS='-O3 -n32 -TARG:platform=IP22 -I/usr/local/include \ -L/usr/local/lib' CXXFLAGS='-O3 -n32 -TARG:platform=IP22 \ -I/usr/local/include -L/usr/local/lib' ./configure --prefix=/usr/local/mysql \ --with-innodb --with-berkeley-db \ --with-libwrap=/usr/local --with-named-curses-libs=/usr/local/lib/libncurses.a
The current port is tested only on a ``sco3.2v5.0.4'' and ``sco3.2v5.0.5'' system. There has also been a lot of progress on a port to ``sco 3.2v4.2''.
For the moment the recommended compiler on OpenServer is gcc 2.95.2. With this you should be able to compile MySQL with just:
CC=gcc CXX=gcc ./configure ... (options)
gcc 2.7.2 in Skunkware 97 does not have GNU
as. You can also use egcs 1.1.2 or newer http://www.egcs.com/. If you are using
egcs 1.1.2 you have to execute the following command: shell> cp -p /usr/include/pthread/stdtypes.h /usr/local/lib/gcc-lib/i386-pc-sco3.2v5.0.5/egcs-2.91.66/include/pthread/
./configure in the `threads/src' directory and
select the SCO OpenServer option. This command copies
`Makefile.SCO5' to `Makefile'.
make.
cd to the `thread/src' directory, and run
make install. make when making MySQL.
safe_mysqld as root, you probably will get
only the default 110 open files per process. mysqld will write a
note about this in the log file.
configure
command should work: shell> ./configure --prefix=/usr/local/mysql --disable-shared
configure command should work: shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \
./configure \
--prefix=/usr/local/mysql \
--with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \
--with-named-curses-libs="-lcurses"
You may get some problems with some include files. In this case, you can
find new SCO-specific include files at http://mysql.com/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz.
You should unpack this file in the `include' directory of your MySQL
source tree. SCO development notes:
mysqld with -lgthreads -lsocket -lgthreads.
malloc. If you encounter problems with memory usage, make sure
that `gmalloc.o' is included in `libgthreads.a' and
`libgthreads.so'.
read(), write(), getmsg(),
connect(), accept(), select(), and
wait(). If you want to install DBI on SCO, you have to edit the `Makefile' in DBI-xxx and each subdirectory.
Note that the following assumes gcc 2.95.2 or newer:
OLD: NEW: CC = cc CC = gcc CCCDLFLAGS = -KPIC -W1,-Bexport CCCDLFLAGS = -fpic CCDLFLAGS = -wl,-Bexport CCDLFLAGS = LD = ld LD = gcc -G -fpic LDDLFLAGS = -G -L/usr/local/lib LDDLFLAGS = -L/usr/local/lib LDFLAGS = -belf -L/usr/local/lib LDFLAGS = -L/usr/local/lib LD = ld LD = gcc -G -fpic OPTIMISE = -Od OPTIMISE = -O1 OLD: CCCFLAGS = -belf -dy -w0 -U M_XENIX -DPERL_SCO5 -I/usr/local/include NEW: CCFLAGS = -U M_XENIX -DPERL_SCO5 -I/usr/local/include
This is because the Perl dynaloader will not load the DBI
modules if they were compiled with icc or cc.
Perl works best when compiled with cc.
You must use a version of MySQL at least as recent as Version 3.22.13 because that version fixes some portability problems under Unixware.
We have been able to compile MySQL with the following configure
command on Unixware Version 7.0.1:
CC=cc CXX=CC ./configure --prefix=/usr/local/mysql
If you want to use gcc, you must use gcc 2.95.2 or
newer.
MySQL uses quite a few open files. Because of this, you should add something like the following to your `CONFIG.SYS' file:
SET EMXOPT=-c -n -h1024
If you don't do this, you will probably run into the following error:
File 'xxxx' not found (Errcode: 24)
When using MySQL with OS/2 Warp 3, FixPack 29 or above is required. With OS/2 Warp 4, FixPack 4 or above is required. This is a requirement of the Pthreads library. MySQL must be installed in a partition that supports long filenames such as HPFS, FAT32, etc.
The `INSTALL.CMD' script must be run from OS/2's own `CMD.EXE' and may not work with replacement shells such as `4OS2.EXE'.
The `scripts/mysql-install-db' script has been renamed. It is now called `install.cmd' and is a REXX script, which will set up the default MySQL security settings and create the WorkPlace Shell icons for MySQL.
Dynamic module support is compiled in but not fully tested. Dynamic modules should be compiled using the Pthreads run-time library.
gcc -Zdll -Zmt -Zcrtdll=pthrdrtl -I../include -I../regex -I.. \
-o example udf_example.cc -L../lib -lmysqlclient udf_example.def
mv example.dll example.udf
Note: Due to limitations in OS/2, UDF module name stems must
not exceed 8 characters. Modules are stored in the `/mysql2/udf'
directory; the safe-mysqld.cmd script will put this directory in
the BEGINLIBPATH environment variable. When using UDF modules,
specified extensions are ignored -- it is assumed to be `.udf'. For
example, in Unix, the shared module might be named `example.so' and you
would load a function from it like this:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example.so";
Is OS/2, the module would be named `example.udf', but you would not specify the module extension:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example";
We are really interested in getting MySQL to work on BeOS, but unfortunately we don't have any person who knows BeOS or has time to do a port.
We are interested in finding someone to do a port, and we will help them with any technical questions they may have while doing the port.
We have previously talked with some BeOS developers that have said that MySQL is 80% ported to BeOS, but we haven't heard from them in a while.
We are really interested in getting MySQL to work on Netware, but unfortunately we don't have any person who knows Netware or has time to do a port.
We are interested in finding someone to do a port, and we will help them with any technical questions they may have while doing the port.
Perl support for MySQL is provided by means of the
DBI/DBD client interface. See section 8.2 MySQL Perl
API. The Perl DBD/DBI client code requires Perl
Version 5.004 or later. The interface will not work if you have
an older version of Perl.
MySQL Perl support also requires that you've installed MySQL client programming support. If you installed MySQL from RPM files, client programs are in the client RPM, but client programming support is in the developer RPM. Make sure you've installed the latter RPM.
As of Version 3.22.8, Perl support is distributed separately from the main MySQL distribution. If you want to install Perl support, the files you will need can be obtained from http://mysql.com/Downloads/Contrib/.
The Perl distributions are provided as compressed tar archives
and have names like `MODULE-VERSION.tar.gz', where MODULE
is the module name and VERSION is the version number. You should
get the Data-Dumper, DBI, and
Msql-Mysql-modules distributions and install them in that order.
The installation procedure is shown below. The example shown is for the
Data-Dumper module, but the procedure is the same for all three
distributions:
shell> gunzip < Data-Dumper-VERSION.tar.gz | tar xvf -This command creates a directory named `Data-Dumper-VERSION'.
shell> cd Data-Dumper-VERSION
shell> perl Makefile.PL shell> make shell> make test shell> make install
The make test command is important because it verifies that the
module is working. Note that when you run that command during the
Msql-Mysql-modules installation to exercise the interface code, the
MySQL server must be running or the test will fail.
It is a good idea to rebuild and reinstall the
Msql-Mysql-modules distribution whenever you install a new release
of MySQL, particularly if you notice symptoms such as all your DBI
scripts dumping core after you upgrade MySQL.
If you don't have the right to install Perl modules in the system directory or if you to install local Perl modules, the following reference may help you:
http://www.iserver.com/support/contrib/perl5/modules.html
Look under the heading Installing New Modules that Require Locally
Installed Modules.
To install the MySQL DBD module with ActiveState Perl on
Windows, you should do the following:
set HTTP_proxy=my.proxy.com:3128
C:\> c:\perl\bin\ppm.pl
DBI: ppm> install DBI
install ftp://ftp.de.uu.net/pub/CPAN/authors/id/JWIED/DBD-mysql-1.2212.x86.ppd
The above should work at least with ActiveState Perl Version 5.6.
If you can't get the above to work, you should instead install the MyODBC driver and connect to MySQL server through ODBC:
use DBI;
$dbh= DBI->connect("DBI:ODBC:$dsn","$user","$password") ||
die "Got error $DBI::errstr when connecting to $dsn\n";
The MySQL Perl distribution contains DBI, DBD:MySQL
and DBD:ODBC.
C: so that you get a
`C:\PERL' directory.
perl works by executing perl -v in a
DOS shell. DBI/DBD InterfaceIf Perl reports that it can't find the `../mysql/mysql.so' module, then the problem is probably that Perl can't locate the shared library `libmysqlclient.so'.
You can fix this by any of the following methods:
Msql-Mysql-modules distribution with perl
Makefile.PL -static -config rather than perl Makefile.PL.
libmysqlclient.so to the directory where your other
shared libraries are located (probably `/usr/lib' or
`/lib').
LD_RUN_PATH environment variable. If you get the following errors from DBD-mysql, you are probably
using gcc (or using an old binary compiled with gcc):
/usr/bin/perl: can't resolve symbol '__moddi3' /usr/bin/perl: can't resolve symbol '__divdi3'
Add -L/usr/lib/gcc-lib/... -lgcc to the link command when the
`mysql.so' library gets built (check the output from make
for `mysql.so' when you compile the Perl client). The -L
option should specify the pathname of the directory where `libgcc.a' is
located on your system.
Another cause of this problem may be that Perl and MySQL aren't both compiled
with gcc. In this case, you can solve the mismatch by compiling
both with gcc.
If you get the following error from Msql-Mysql-modules when you
run the tests:
t/00base............install_driver(mysql) failed: Can't load '../blib/arch/auto/DBD/mysql/mysql.so' for module DBD::mysql: ../blib/arch/auto/DBD/mysql/mysql.so: undefined symbol: uncompress at /usr/lib/perl5/5.00503/i586-linux/DynaLoader.pm line 169.
it means that you need to include the compression library, -lz, to the link line. This can be doing the following change in the file `lib/DBD/mysql/Install.pm':
$sysliblist .= " -lm"; to $sysliblist .= " -lm -lz";
After this, you must run 'make realclean' and then proceed with the installation from the beginning.
If you want to use the Perl module on a system that doesn't support dynamic
linking (like SCO) you can generate a static version of Perl that includes
DBI and DBD-mysql. The way this works is that you
generate a version of Perl with the DBI code linked in and install
it on top of your current Perl. Then you use that to build a version of Perl
that additionally has the DBD code linked in, and install that.
On SCO, you must have the following environment variables set:
shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib or shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:/usr/skunk/man:
First, create a Perl that includes a statically linked DBI by
running these commands in the directory where your DBI distribution
is located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Then you must install the new Perl. The output of make perl will
indicate the exact make command you will need to execute to perform
the installation. On SCO, this is make -f Makefile.aperl inst_perl
MAP_TARGET=perl.
Next, use the just-created Perl to create another Perl that also includes a
statically-linked DBD::mysql by running these commands in the
directory where your Msql-Mysql-modules distribution is located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Finally, you should install this new Perl. Again, the output of make
perl indicates the command to use.
This chapter provides a tutorial introduction to MySQL by showing how to use
the mysql client program to create and use a simple database.
mysql (sometimes referred to as the ``terminal monitor'' or just
``monitor'') is an interactive program that allows you to connect to a MySQL
server, run queries, and view the results. mysql may also be used
in batch mode: you place your queries in a file beforehand, then tell
mysql to execute the contents of the file. Both ways of using
mysql are covered here.
To see a list of options provided by mysql, invoke it with the
--help option:
shell> mysql --help
This chapter assumes that mysql is installed on your machine and
that a MySQL server is available to which you can connect. If this is not true,
contact your MySQL administrator. (If you are the administrator, you
will need to consult other sections of this manual.)
This chapter describes the entire process of setting up and using a database. If you are interested only in accessing an already-existing database, you may want to skip over the sections that describe how to create the database and the tables it contains.
Because this chapter is tutorial in nature, many details are necessarily left out. Consult the relevant sections of the manual for more information on the topics covered here.
To connect to the server, you'll usually need to provide a MySQL user name
when you invoke mysql and, most likely, a password. If the server
runs on a machine other than the one where you log in, you'll also need to
specify a hostname. Contact your administrator to find out what connection
parameters you should use to connect (that is, what host, user name, and
password to use). Once you know the proper parameters, you should be able to
connect like this:
shell> mysql -h host -u user -p Enter password: ********
The ******** represents your password; enter it when
mysql displays the Enter password: prompt.
If that works, you should see some introductory information followed by a
mysql> prompt:
shell> mysql -h host -u user -p Enter password: ******** Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 459 to server version: 3.22.20a-log Type 'help' for help. mysql>
The prompt tells you that mysql is ready for you to enter
commands.
Some MySQL installations allow users to connect as the anonymous (unnamed)
user to the server running on the local host. If this is the case on your
machine, you should be able to connect to that server by invoking
mysql without any options:
shell> mysql
After you have connected successfully, you can disconnect any time by typing
QUIT at the mysql> prompt:
mysql> QUIT Bye
You can also disconnect by pressing Control-D.
Most examples in the following sections assume you are connected to the
server. They indicate this by the mysql> prompt.
Make sure you are connected to the server, as discussed in the previous
section. Doing so will not in itself select any database to work with, but
that's okay. At this point, it's more important to find out a little about how
to issue queries than to jump right in creating tables, loading data into them,
and retrieving data from them. This section describes the basic principles of
entering commands, using several queries you can try out to familiarise yourself
with how mysql works.
Here's a simple command that asks the server to tell you its version number
and the current date. Type it in as shown below following the
mysql> prompt and press Enter:
mysql> SELECT VERSION(), CURRENT_DATE; +--------------+--------------+ | version() | CURRENT_DATE | +--------------+--------------+ | 3.22.20a-log | 1999-03-19 | +--------------+--------------+ 1 row in set (0.01 sec) mysql>
This query illustrates several things about mysql:
QUIT,
mentioned earlier, is one of them. We'll get to others later.)
mysql sends it to the server for
execution and displays the results, then prints another mysql>
to indicate that it is ready for another command.
mysql displays query output as a table (rows and columns).
The first row contains labels for the columns. The rows following are the
query results. Normally, column labels are the names of the columns you fetch
from database tables. If you're retrieving the value of an expression rather
than a table column (as in the example just shown), mysql labels
the column using the expression itself.
mysql shows how many rows were returned and how long the
query took to execute, which gives you a rough idea of server performance.
These values are imprecise because they represent wall clock time (not CPU or
machine time), and because they are affected by factors such as server load
and network latency. (For brevity, the ``rows in set'' line is not shown in
the remaining examples in this chapter.) Keywords may be entered in any lettercase. The following queries are equivalent:
mysql> SELECT VERSION(), CURRENT_DATE; mysql> select version(), current_date; mysql> SeLeCt vErSiOn(), current_DATE;
Here's another query. It demonstrates that you can use mysql as
a simple calculator:
mysql> SELECT SIN(PI()/4), (4+1)*5; +-------------+---------+ | SIN(PI()/4) | (4+1)*5 | +-------------+---------+ | 0.707107 | 25 | +-------------+---------+
The commands shown thus far have been relatively short, single-line statements. You can even enter multiple statements on a single line. Just end each one with a semicolon:
mysql> SELECT VERSION(); SELECT NOW(); +--------------+ | version() | +--------------+ | 3.22.20a-log | +--------------+ +---------------------+ | NOW() | +---------------------+ | 1999-03-19 00:15:33 | +---------------------+
A command need not be given all on a single line, so lengthy commands that
require several lines are not a problem. mysql determines where
your statement ends by looking for the terminating semicolon, not by looking for
the end of the input line. (In other words, mysql accepts
free-format input: it collects input lines but does not execute them until it
sees the semicolon.)
Here's a simple multiple-line statement:
mysql> SELECT
-> USER()
-> ,
-> CURRENT_DATE;
+--------------------+--------------+
| USER() | CURRENT_DATE |
+--------------------+--------------+
| joesmith@localhost | 1999-03-18 |
+--------------------+--------------+
In this example, notice how the prompt changes from mysql> to
-> after you enter the first line of a multiple-line query. This
is how mysql indicates that it hasn't seen a complete statement and
is waiting for the rest. The prompt is your friend, because it provides valuable
feedback. If you use that feedback, you will always be aware of what
mysql is waiting for.
If you decide you don't want to execute a command that you are in the process
of entering, cancel it by typing \c:
mysql> SELECT
-> USER()
-> \c
mysql>
Here, too, notice the prompt. It switches back to mysql>
after you type \c, providing feedback to indicate that
mysql is ready for a new command.
The following table shows each of the prompts you may see and summarises what
they mean about the state that mysql is in:
| Prompt | Meaning |
mysql> |
Ready for new command. |
-> |
Waiting for next line of multiple-line command. |
'> |
Waiting for next line, collecting a string that begins with a single quote (`''). |
"> |
Waiting for next line, collecting a string that begins with a double quote (`"'). |
Multiple-line statements commonly occur by accident when you intend to issue
a command on a single line, but forget the terminating semicolon. In this case,
mysql waits for more input:
mysql> SELECT USER()
->
If this happens to you (you think you've entered a statement but the only
response is a -> prompt), most likely mysql is
waiting for the semicolon. If you don't notice what the prompt is telling you,
you might sit there for a while before realising what you need to do. Enter a
semicolon to complete the statement, and mysql will execute it:
mysql> SELECT USER()
-> ;
+--------------------+
| USER() |
+--------------------+
| joesmith@localhost |
+--------------------+
The '> and "> prompts occur during string
collection. In MySQL, you can write strings surrounded by either
`'' or `"' characters (for example,
'hello' or "goodbye"), and mysql lets you
enter strings that span multiple lines. When you see a '> or
"> prompt, it means that you've entered a line containing a
string that begins with a `'' or `"' quote character,
but have not yet entered the matching quote that terminates the string. That's
fine if you really are entering a multiple-line string, but how likely is that?
Not very. More often, the '> and "> prompts
indicate that you've inadvertantly left out a quote character. For example:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
">
If you enter this SELECT statement, then press Enter and wait
for the result, nothing will happen. Instead of wondering why this query takes
so long, notice the clue provided by the "> prompt. It tells you
that mysql expects to see the rest of an unterminated string. (Do
you see the error in the statement? The string "Smith is missing
the second quote.)
At this point, what do you do? The simplest thing is to cancel the command.
However, you cannot just type \c in this case, because
mysql interprets it as part of the string that it is collecting!
Instead, enter the closing quote character (so mysql knows you've
finished the string), then type \c:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
"> "\c
mysql>
The prompt changes back to mysql>, indicating that
mysql is ready for a new command.
It's important to know what the '> and ">
prompts signify, because if you mistakenly enter an unterminated string, any
further lines you type will appear to be ignored by mysql --
including a line containing QUIT! This can be quite confusing,
especially if you don't know that you need to supply the terminating quote
before you can cancel the current command.
Now that you know how to enter commands, it's time to access a database.
Suppose you have several pets in your home (your menagerie) and you'd like to keep track of various types of information about them. You can do so by creating tables to hold your data and loading them with the desired information. Then you can answer different sorts of questions about your animals by retrieving data from the tables. This section shows you how to:
The menagerie database will be simple (deliberately), but it is not difficult
to think of real-world situations in which a similar type of database might be
used. For example, a database like this could be used by a farmer to keep track
of livestock, or by a veterinarian to keep track of patient records. A menagerie
distribution containing some of the queries and sample data used in the
following sections can be obtained from the MySQL web site. It's available in
either compressed tar format (http://mysql.com/Downloads/Contrib/Examples/menagerie.tar.gz)
or Zip format (http://mysql.com/Downloads/Contrib/Examples/menagerie.zip).
Use the SHOW statement to find out what databases currently
exist on the server:
mysql> SHOW DATABASES; +----------+ | Database | +----------+ | mysql | | test | | tmp | +----------+
The list of databases is probably different on your machine, but the
mysql and test databases are likely to be among them.
The mysql database is required because it describes user access
privileges. The test database is often provided as a workspace for
users to try things out.
If the test database exists, try to access it:
mysql> USE test Database changed
Note that USE, like QUIT, does not require a
semicolon. (You can terminate such statements with a semicolon if you like; it
does no harm.) The USE statement is special in another way, too: it
must be given on a single line.
You can use the test database (if you have access to it) for the
examples that follow, but anything you create in that database can be removed by
anyone else with access to it. For this reason, you should probably ask your
MySQL administrator for permission to use a database of your own. Suppose you
want to call yours menagerie. The administrator needs to execute a
command like this:
mysql> GRANT ALL ON menagerie.* TO your_mysql_name;
where your_mysql_name is the MySQL user name assigned to you.
If the administrator creates your database for you when setting up your permissions, you can begin using it. Otherwise, you need to create it yourself:
mysql> CREATE DATABASE menagerie;
Under Unix, database names are case sensitive (unlike SQL keywords), so you
must always refer to your database as menagerie, not as
Menagerie, MENAGERIE, or some other variant. This is
also true for table names. (Under Windows, this restriction does not apply,
although you must refer to databases and tables using the same lettercase
throughout a given query.)
Creating a database does not select it for use; you must do that explicitly.
To make menagerie the current database, use this command:
mysql> USE menagerie Database changed
Your database needs to be created only once, but you must select it for use
each time you begin a mysql session. You can do this by issuing a
USE statement as shown above. Alternatively, you can select the
database on the command line when you invoke mysql. Just specify
its name after any connection parameters that you might need to provide. For
example:
shell> mysql -h host -u user -p menagerie Enter password: ********
Note that menagerie is not your password on the command just
shown. If you want to supply your password on the command line after the
-p option, you must do so with no intervening space (for example,
as -pmypassword, not as -p mypassword). However,
putting your password on the command line is not recommended, because doing so
exposes it to snooping by other users logged in on your machine.
Creating the database is the easy part, but at this point it's empty, as
SHOW TABLES will tell you:
mysql> SHOW TABLES; Empty set (0.00 sec)
The harder part is deciding what the structure of your database should be: what tables you will need and what columns will be in each of them.
You'll want a table that contains a record for each of your pets. This can be
called the pet table, and it should contain, as a bare minimum,
each animal's name. Because the name by itself is not very interesting, the
table should contain other information. For example, if more than one person in
your family keeps pets, you might want to list each animal's owner. You might
also want to record some basic descriptive information such as species and sex.
How about age? That might be of interest, but it's not a good thing to store in a database. Age changes as time passes, which means you'd have to update your records often. Instead, it's better to store a fixed value such as date of birth. Then, whenever you need age, you can calculate it as the difference between the current date and the birth date. MySQL provides functions for doing date arithmetic, so this is not difficult. Storing birth date rather than age has other advantages, too:
You can probably think of other types of information that would be useful in
the pet table, but the ones identified so far are sufficient for
now: name, owner, species, sex, birth, and death.
Use a CREATE TABLE statement to specify the layout of your
table:
mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
-> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);
VARCHAR is a good choice for the name,
owner, and species columns because the column values
will vary in length. The lengths of those columns need not all be the same, and
need not be 20. You can pick any length from 1 to
255, whatever seems most reasonable to you. (If you make a poor
choice and it turns out later that you need a longer field, MySQL provides an
ALTER TABLE statement.)
Animal sex can be represented in a variety of ways, for example,
"m" and "f", or perhaps "male" and
"female". It's simplest to use the single characters
"m" and "f".
The use of the DATE data type for the birth and
death columns is a fairly obvious choice.
Now that you have created a table, SHOW TABLES should produce
some output:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | pet | +---------------------+
To verify that your table was created the way you expected, use a
DESCRIBE statement:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
You can use DESCRIBE any time, for example, if you forget the
names of the columns in your table or what types they are.
After creating your table, you need to populate it. The LOAD
DATA and INSERT statements are useful for this.
Suppose your pet records can be described as shown below. (Observe that MySQL
expects dates in YYYY-MM-DD format; this may be different than what
you are used to.)
| name | owner | species | sex | birth | death |
| Fluffy | Harold | cat | f | 1993-02-04 | |
| Claws | Gwen | cat | m | 1994-03-17 | |
| Buffy | Harold | dog | f | 1989-05-13 | |
| Fang | Benny | dog | m | 1990-08-27 | |
| Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 |
| Chirpy | Gwen | bird | f | 1998-09-11 | |
| Whistler | Gwen | bird | 1997-12-09 | ||
| Slim | Benny | snake | m | 1996-04-29 |
Because you are beginning with an empty table, an easy way to populate it is to create a text file containing a row for each of your animals, then load the contents of the file into the table with a single statement.
You could create a text file `pet.txt' containing one record per
line, with values separated by tabs, and given in the order in which the columns
were listed in the CREATE TABLE statement. For missing values (such
as unknown sexes or death dates for animals that are still living), you can use
NULL values. To represent these in your text file, use
\N. For example, the record for Whistler the bird would look like
this (where the whitespace between values is a single tab character):
| name | owner | species | sex | birth | death |
Whistler |
Gwen |
bird |
\N |
1997-12-09 |
\N |
To load the text file `pet.txt' into the pet table, use
this command:
mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;
You can specify the column value separator and end of line marker explicitly
in the LOAD DATA statement if you wish, but the defaults are tab
and linefeed. These are sufficient for the statement to read the file
`pet.txt' properly.
When you want to add new records one at a time, the INSERT
statement is useful. In its simplest form, you supply values for each column, in
the order in which the columns were listed in the CREATE TABLE
statement. Suppose Diane gets a new hamster named Puffball. You could add a new
record using an INSERT statement like this:
mysql> INSERT INTO pet
-> VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);
Note that string and date values are specified as quoted strings here. Also,
with INSERT, you can insert NULL directly to represent
a missing value. You do not use \N like you do with LOAD
DATA.
From this example, you should be able to see that there would be a lot more
typing involved to load your records initially using several INSERT
statements rather than a single LOAD DATA statement.
The SELECT statement is used to pull information from a table.
The general form of the statement is:
SELECT what_to_select FROM which_table WHERE conditions_to_satisfy
what_to_select indicates what you want to see. This can be a
list of columns, or * to indicate ``all columns.''
which_table indicates the table from which you want to retrieve
data. The WHERE clause is optional. If it's present,
conditions_to_satisfy specifies conditions that rows must satisfy
to qualify for retrieval.
The simplest form of SELECT retrieves everything from a table:
mysql> SELECT * FROM pet; +----------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+--------+---------+------+------------+------------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Fang | Benny | dog | m | 1990-08-27 | NULL | | Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 | | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+--------+---------+------+------------+------------+
This form of SELECT is useful if you want to review your entire
table, for instance, after you've just loaded it with your initial dataset. As
it happens, the output just shown reveals an error in your data file: Bowser
appears to have been born after he died! Consulting your original pedigree
papers, you find that the correct birth year is 1989, not 1998.
There are are least a couple of ways to fix this:
DELETE and LOAD DATA: mysql> SET AUTOCOMMIT=1; # Used for quick re-create of the table mysql> DELETE FROM pet; mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;However, if you do this, you must also re-enter the record for Puffball.
UPDATE statement: mysql> UPDATE pet SET birth = "1989-08-31" WHERE name = "Bowser";
As shown above, it is easy to retrieve an entire table. But typically you don't want to do that, particularly when the table becomes large. Instead, you're usually more interested in answering a particular question, in which case you specify some constraints on the information you want. Let's look at some selection queries in terms of questions about your pets that they answer.
You can select only particular rows from your table. For example, if you want to verify the change that you made to Bowser's birth date, select Bowser's record like this:
mysql> SELECT * FROM pet WHERE name = "Bowser"; +--------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+------------+ | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+-------+---------+------+------------+------------+
The output confirms that the year is correctly recorded now as 1989, not 1998.
String comparisons are normally case insensitive, so you can specify the name
as "bowser", "BOWSER", etc. The query result will be
the same.
You can specify conditions on any column, not just name. For
example, if you want to know which animals were born after 1998, test the
birth column:
mysql> SELECT * FROM pet WHERE birth >= "1998-1-1"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+
You can combine conditions, for example, to locate female dogs:
mysql> SELECT * FROM pet WHERE species = "dog" AND sex = "f"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The preceding query uses the AND logical operator. There is also
an OR operator:
mysql> SELECT * FROM pet WHERE species = "snake" OR species = "bird"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | +----------+-------+---------+------+------------+-------+
AND and OR may be intermixed. If you do that, it's
a good idea to use parentheses to indicate how conditions should be grouped:
mysql> SELECT * FROM pet WHERE (species = "cat" AND sex = "m")
-> OR (species = "dog" AND sex = "f");
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
If you don't want to see entire rows from your table, just name the columns
in which you're interested, separated by commas. For example, if you want to
know when your animals were born, select the name and
birth columns:
mysql> SELECT name, birth FROM pet; +----------+------------+ | name | birth | +----------+------------+ | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Buffy | 1989-05-13 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Puffball | 1999-03-30 | +----------+------------+
To find out who owns pets, use this query:
mysql> SELECT owner FROM pet; +--------+ | owner | +--------+ | Harold | | Gwen | | Harold | | Benny | | Diane | | Gwen | | Gwen | | Benny | | Diane | +--------+
However, notice that the query simply retrieves the
owner field from each record, and some of them appear more than
once. To minimise the output, retrieve each unique output record just once by
adding the keyword DISTINCT:
mysql> SELECT DISTINCT owner FROM pet; +--------+ | owner | +--------+ | Benny | | Diane | | Gwen | | Harold | +--------+
You can use a WHERE clause to combine row selection with column
selection. For example, to get birth dates for dogs and cats only, use this
query:
mysql> SELECT name, species, birth FROM pet
-> WHERE species = "dog" OR species = "cat";
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
| Fang | dog | 1990-08-27 |
| Bowser | dog | 1989-08-31 |
+--------+---------+------------+
You may have noticed in the preceding examples that the result rows are
displayed in no particular order. However, it's often easier to examine query
output when the rows are sorted in some meaningful way. To sort a result, use an
ORDER BY clause.
Here are animal birthdays, sorted by date:
mysql> SELECT name, birth FROM pet ORDER BY birth; +----------+------------+ | name | birth | +----------+------------+ | Buffy | 1989-05-13 | | Bowser | 1989-08-31 | | Fang | 1990-08-27 | | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Slim | 1996-04-29 | | Whistler | 1997-12-09 | | Chirpy | 1998-09-11 | | Puffball | 1999-03-30 | +----------+------------+
To sort in reverse order, add the DESC (descending) keyword to
the name of the column you are sorting by:
mysql> SELECT name, birth FROM pet ORDER BY birth DESC; +----------+------------+ | name | birth | +----------+------------+ | Puffball | 1999-03-30 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Claws | 1994-03-17 | | Fluffy | 1993-02-04 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Buffy | 1989-05-13 | +----------+------------+
You can sort on multiple columns. For example, to sort by type of animal, then by birth date within animal type with youngest animals first, use the following query:
mysql> SELECT name, species, birth FROM pet ORDER BY species, birth DESC; +----------+---------+------------+ | name | species | birth | +----------+---------+------------+ | Chirpy | bird | 1998-09-11 | | Whistler | bird | 1997-12-09 | | Claws | cat | 1994-03-17 | | Fluffy | cat | 1993-02-04 | | Fang | dog | 1990-08-27 | | Bowser | dog | 1989-08-31 | | Buffy | dog | 1989-05-13 | | Puffball | hamster | 1999-03-30 | | Slim | snake | 1996-04-29 | +----------+---------+------------+
Note that the DESC keyword applies only to the column name
immediately preceding it (birth); species values are
still sorted in ascending order.
MySQL provides several functions that you can use to perform calculations on dates, for example, to calculate ages or extract parts of dates.
To determine how many years old each of your pets is, compute the difference in the year part of the current date and the birth date, then subtract one if the current date occurs earlier in the calendar year than the birth date. The following query shows, for each pet, the birth date, the current date, and the age in years.
mysql> SELECT name, birth, CURRENT_DATE,
-> (YEAR(CURRENT_DATE)-YEAR(birth))
-> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
-> AS age
-> FROM pet;
+----------+------------+--------------+------+
| name | birth | CURRENT_DATE | age |
+----------+------------+--------------+------+
| Fluffy | 1993-02-04 | 2001-08-29 | 8 |
| Claws | 1994-03-17 | 2001-08-29 | 7 |
| Buffy | 1989-05-13 | 2001-08-29 | 12 |
| Fang | 1990-08-27 | 2001-08-29 | 11 |
| Bowser | 1989-08-31 | 2001-08-29 | 11 |
| Chirpy | 1998-09-11 | 2001-08-29 | 2 |
| Whistler | 1997-12-09 | 2001-08-29 | 3 |
| Slim | 1996-04-29 | 2001-08-29 | 5 |
| Puffball | 1999-03-30 | 2001-08-29 | 2 |
+----------+------------+--------------+------+
Here, YEAR() pulls out the year part of a date and
RIGHT() pulls off the rightmost five characters that represent the
MM-DD (calendar year) part of the date. The part of the expression
that compares the MM-DD values evaluates to 1 or 0, which adjusts
the year difference down a year if CURRENT_DATE occurs earlier in
the year than birth. The full expression is somewhat ungainly, so
an alias (age) is used to make the output column label more
meaningful.
The query works, but the result could be scanned more easily if the rows were
presented in some order. This can be done by adding an ORDER BY
name clause to sort the output by name:
mysql> SELECT name, birth, CURRENT_DATE,
-> (YEAR(CURRENT_DATE)-YEAR(birth))
-> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
-> AS age
-> FROM pet ORDER BY name;
+----------+------------+--------------+------+
| name | birth | CURRENT_DATE | age |
+----------+------------+--------------+------+
| Bowser | 1989-08-31 | 2001-08-29 | 11 |
| Buffy | 1989-05-13 | 2001-08-29 | 12 |
| Chirpy | 1998-09-11 | 2001-08-29 | 2 |
| Claws | 1994-03-17 | 2001-08-29 | 7 |
| Fang | 1990-08-27 | 2001-08-29 | 11 |
| Fluffy | 1993-02-04 | 2001-08-29 | 8 |
| Puffball | 1999-03-30 | 2001-08-29 | 2 |
| Slim | 1996-04-29 | 2001-08-29 | 5 |
| Whistler | 1997-12-09 | 2001-08-29 | 3 |
+----------+------------+--------------+------+
To sort the output by age rather than name, just
use a different ORDER BY clause:
mysql> SELECT name, birth, CURRENT_DATE,
-> (YEAR(CURRENT_DATE)-YEAR(birth))
-> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
-> AS age
-> FROM pet ORDER BY age;
+----------+------------+--------------+------+
| name | birth | CURRENT_DATE | age |
+----------+------------+--------------+------+
| Chirpy | 1998-09-11 | 2001-08-29 | 2 |
| Puffball | 1999-03-30 | 2001-08-29 | 2 |
| Whistler | 1997-12-09 | 2001-08-29 | 3 |
| Slim | 1996-04-29 | 2001-08-29 | 5 |
| Claws | 1994-03-17 | 2001-08-29 | 7 |
| Fluffy | 1993-02-04 | 2001-08-29 | 8 |
| Fang | 1990-08-27 | 2001-08-29 | 11 |
| Bowser | 1989-08-31 | 2001-08-29 | 11 |
| Buffy | 1989-05-13 | 2001-08-29 | 12 |
+----------+------------+--------------+------+
A similar query can be used to determine age at death for animals that have
died. You determine which animals these are by checking whether or not the
death value is NULL. Then, for those with
non-NULL values, compute the difference between the
death and birth values:
mysql> SELECT name, birth, death,
-> (YEAR(death)-YEAR(birth)) - (RIGHT(death,5)<RIGHT(birth,5))
-> AS age
-> FROM pet WHERE death IS NOT NULL ORDER BY age;
+--------+------------+------------+------+
| name | birth | death | age |
+--------+------------+------------+------+
| Bowser | 1989-08-31 | 1995-07-29 | 5 |
+--------+------------+------------+------+
The query uses death IS NOT NULL rather than death
<> NULL because NULL is a special value. This is
explained later. See section 3.3.4.6
Working with NULL Values.
What if you want to know which animals have birthdays next month? For this
type of calculation, year and day are irrelevant; you simply want to extract the
month part of the birth column. MySQL provides several date-part
extraction functions, such as YEAR(), MONTH(), and
DAYOFMONTH(). MONTH() is the appropriate function
here. To see how it works, run a simple query that displays the value of both
birth and MONTH(birth):
mysql> SELECT name, birth, MONTH(birth) FROM pet; +----------+------------+--------------+ | name | birth | MONTH(birth) | +----------+------------+--------------+ | Fluffy | 1993-02-04 | 2 | | Claws | 1994-03-17 | 3 | | Buffy | 1989-05-13 | 5 | | Fang | 1990-08-27 | 8 | | Bowser | 1989-08-31 | 8 | | Chirpy | 1998-09-11 | 9 | | Whistler | 1997-12-09 | 12 | | Slim | 1996-04-29 | 4 | | Puffball | 1999-03-30 | 3 | +----------+------------+--------------+
Finding animals with birthdays in the upcoming month is easy, too. Suppose
the current month is April. Then the month value is 4 and you look
for animals born in May (month 5) like this:
mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5; +-------+------------+ | name | birth | +-------+------------+ | Buffy | 1989-05-13 | +-------+------------+
There is a small complication if the current month is December, of course.
You don't just add one to the month number (12) and look for
animals born in month 13, because there is no such month. Instead, you look for
animals born in January (month 1).
You can even write the query so that it works no matter what the current
month is. That way you don't have to use a particular month number in the query.
DATE_ADD() allows you to add a time interval to a given date. If
you add a month to the value of NOW(), then extract the month part
with MONTH(), the result produces the month in which to look for
birthdays:
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MONTH(DATE_ADD(NOW(), INTERVAL 1 MONTH));
A different way to accomplish the same task is to add 1 to get
the next month after the current one (after using the modulo function
(MOD) to wrap around the month value to 0 if it is
currently 12):
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MOD(MONTH(NOW()), 12) + 1;
Note that MONTH returns a number between 1 and 12. And
MOD(something,12) returns a number between 0 and 11. So the
addition has to be after the MOD(), otherwise we would go from
November (11) to January (1).
NULL ValuesThe NULL value can be surprising until you get used to it.
Conceptually, NULL means missing value or unknown value and it is
treated somewhat differently than other values. To test for NULL,
you cannot use the arithmetic comparison operators such as =,
<, or <>. To demonstrate this for yourself,
try the following query:
mysql> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL; +----------+-----------+----------+----------+ | 1 = NULL | 1 <> NULL | 1 < NULL | 1 > NULL | +----------+-----------+----------+----------+ | NULL | NULL | NULL | NULL | +----------+-----------+----------+----------+
Clearly you get no meaningful results from these comparisons. Use the
IS NULL and IS NOT NULL operators instead:
mysql> SELECT 1 IS NULL, 1 IS NOT NULL; +-----------+---------------+ | 1 IS NULL | 1 IS NOT NULL | +-----------+---------------+ | 0 | 1 | +-----------+---------------+
In MySQL, 0 or NULL means false and anything else means true.
The default truth value from a boolean operation is 1.
This special treatment of NULL is why, in the previous section,
it was necessary to determine which animals are no longer alive using
death IS NOT NULL instead of death <> NULL.
MySQL provides standard SQL pattern matching as well as a form of pattern
matching based on extended regular expressions similar to those used by Unix
utilities such as vi, grep, and sed.
SQL pattern matching allows you to use `_' to match any single
character and `%' to match an arbitrary number of characters
(including zero characters). In MySQL, SQL patterns are case insensitive by
default. Some examples are shown below. Note that you do not use =
or <> when you use SQL patterns; use the LIKE or
NOT LIKE comparison operators instead.
To find names beginning with `b':
mysql> SELECT * FROM pet WHERE name LIKE "b%"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
To find names ending with `fy':
mysql> SELECT * FROM pet WHERE name LIKE "%fy"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a `w':
mysql> SELECT * FROM pet WHERE name LIKE "%w%"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
To find names containing exactly five characters, use the `_' pattern character:
mysql> SELECT * FROM pet WHERE name LIKE "_____"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The other type of pattern matching provided by MySQL uses extended regular
expressions. When you test for a match for this type of pattern, use the
REGEXP and NOT REGEXP operators (or RLIKE
and NOT RLIKE, which are synonyms).
Some characteristics of extended regular expressions are:
To demonstrate how extended regular expressions work, the LIKE
queries shown above are rewritten below to use REGEXP.
To find names beginning with `b', use `^' to match the beginning of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "^b"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
Prior to MySQL Version 3.23.4, REGEXP is case sensitive, and the
previous query will return no rows. To match either lowercase or uppercase
`b', use this query instead:
mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]";
From MySQL 3.23.4 on, to force a REGEXP comparison to be case
sensitive, use the BINARY keyword to make one of the strings a
binary string. This query will match only lowercase `b' at the
beginning of a name:
mysql> SELECT * FROM pet WHERE name REGEXP BINARY "^b";
To find names ending with `fy', use `$' to match the end of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "fy$"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a lowercase or uppercase `w', use this query:
mysql> SELECT * FROM pet WHERE name REGEXP "w"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
Because a regular expression pattern matches if it occurs anywhere in the value, it is not necessary in the previous query to put a wild card on either side of the pattern to get it to match the entire value like it would be if you used a SQL pattern.
To find names containing exactly five characters, use `^' and `$' to match the beginning and end of the name, and five instances of `.' in between:
mysql> SELECT * FROM pet WHERE name REGEXP "^.....$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
You could also write the previous query using the `{n}'
``repeat-n-times'' operator:
mysql> SELECT * FROM pet WHERE name REGEXP "^.{5}$";
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
Databases are often used to answer the question, ``How often does a certain type of data occur in a table?'' For example, you might want to know how many pets you have, or how many pets each owner has, or you might want to perform various kinds of censuses on your animals.
Counting the total number of animals you have is the same question as ``How
many rows are in the pet table?'' because there is one record per
pet. The COUNT() function counts the number of
non-NULL results, so the query to count your animals looks like
this:
mysql> SELECT COUNT(*) FROM pet; +----------+ | COUNT(*) | +----------+ | 9 | +----------+
Earlier, you retrieved the names of the people who owned pets. You can use
COUNT() if you want to find out how many pets each owner has:
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner; +--------+----------+ | owner | COUNT(*) | +--------+----------+ | Benny | 2 | | Diane | 2 | | Gwen | 3 | | Harold | 2 | +--------+----------+
Note the use of GROUP BY to group together all records for each
owner. Without it, all you get is an error message:
mysql> SELECT owner, COUNT(owner) FROM pet; ERROR 1140 at line 1: Mixing of GROUP columns (MIN(),MAX(),COUNT()...) with no GROUP columns is illegal if there is no GROUP BY clause
COUNT() and GROUP BY are useful for characterising
your data in various ways. The following examples show different ways to perform
animal census operations.
Number of animals per species:
mysql> SELECT species, COUNT(*) FROM pet GROUP BY species; +---------+----------+ | species | COUNT(*) | +---------+----------+ | bird | 2 | | cat | 2 | | dog | 3 | | hamster | 1 | | snake | 1 | +---------+----------+
Number of animals per sex:
mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex; +------+----------+ | sex | COUNT(*) | +------+----------+ | NULL | 1 | | f | 4 | | m | 4 | +------+----------+
(In this output, NULL indicates sex unknown.)
Number of animals per combination of species and sex:
mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex; +---------+------+----------+ | species | sex | COUNT(*) | +---------+------+----------+ | bird | NULL | 1 | | bird | f | 1 | | cat | f | 1 | | cat | m | 1 | | dog | f | 1 | | dog | m | 2 | | hamster | f | 1 | | snake | m | 1 | +---------+------+----------+
You need not retrieve an entire table when you use COUNT(). For
example, the previous query, when performed just on dogs and cats, looks like
this:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE species = "dog" OR species = "cat"
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
+---------+------+----------+
Or, if you wanted the number of animals per sex only for known-sex animals:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE sex IS NOT NULL
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| bird | f | 1 |
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
| hamster | f | 1 |
| snake | m | 1 |
+---------+------+----------+
The pet table keeps track of which pets you have. If you want to
record other information about them, such as events in their lives like visits
to the vet or when litters are born, you need another table. What should this
table look like? It needs:
Given these considerations, the CREATE TABLE statement for the
event table might look like this:
mysql> CREATE TABLE event (name VARCHAR(20), date DATE,
-> type VARCHAR(15), remark VARCHAR(255));
As with the pet table, it's easiest to load the initial records
by creating a tab-delimited text file containing the information:
| name | date | type | remark |
| Fluffy | 1995-05-15 | litter | 4 kittens, 3 female, 1 male |
| Buffy | 1993-06-23 | litter | 5 puppies, 2 female, 3 male |
| Buffy | 1994-06-19 | litter | 3 puppies, 3 female |
| Chirpy | 1999-03-21 | vet | needed beak straightened |
| Slim | 1997-08-03 | vet | broken rib |
| Bowser | 1991-10-12 | kennel | |
| Fang | 1991-10-12 | kennel | |
| Fang | 1998-08-28 | birthday | Gave him a new chew toy |
| Claws | 1998-03-17 | birthday | Gave him a new flea collar |
| Whistler | 1998-12-09 | birthday | First birthday |
Load the records like this:
mysql> LOAD DATA LOCAL INFILE "event.txt" INTO TABLE event;
Based on what you've learned from the queries you've run on the
pet table, you should be able to perform retrievals on the records
in the event table; the principles are the same. But when is the
event table by itself insufficient to answer questions you might
ask?
Suppose you want to find out the ages of each pet when they had their
litters. The event table indicates when this occurred, but to
calculate the age of the mother, you need her birth date. Because that is stored
in the pet table, you need both tables for the query:
mysql> SELECT pet.name, (TO_DAYS(date) - TO_DAYS(birth))/365 AS age, remark
-> FROM pet, event
-> WHERE pet.name = event.name AND type = "litter";
+--------+------+-----------------------------+
| name | age | remark |
+--------+------+-----------------------------+
| Fluffy | 2.27 | 4 kittens, 3 female, 1 male |
| Buffy | 4.12 | 5 puppies, 2 female, 3 male |
| Buffy | 5.10 | 3 puppies, 3 female |
+--------+------+-----------------------------+
There are several things to note about this query:
FROM clause lists two tables because the query needs to
pull information from both of them.
name column. The query uses
WHERE clause to match up records in the two tables based on the
name values.
name column occurs in both tables, you must be
specific about which table you mean when referring to the column. This is done
by prepending the table name to the column name. You need not have two different tables to perform a join. Sometimes it is
useful to join a table to itself, if you want to compare records in a table to
other records in that same table. For example, to find breeding pairs among your
pets, you can join the pet table with itself to pair up males and
females of like species:
mysql> SELECT p1.name, p1.sex, p2.name, p2.sex, p1.species
-> FROM pet AS p1, pet AS p2
-> WHERE p1.species = p2.species AND p1.sex = "f" AND p2.sex = "m";
+--------+------+--------+------+---------+
| name | sex | name | sex | species |
+--------+------+--------+------+---------+
| Fluffy | f | Claws | m | cat |
| Buffy | f | Fang | m | dog |
| Buffy | f | Bowser | m | dog |
+--------+------+--------+------+---------+
In this query, we specify aliases for the table name in order to refer to the columns and keep straight which instance of the table each column reference is associated with.
What if you forget the name of a database or table, or what the structure of a given table is (for example, what its columns are called)? MySQL addresses this problem through several statements that provide information about the databases and tables it supports.
You have already seen SHOW DATABASES, which lists the databases
managed by the server. To find out which database is currently selected, use the
DATABASE() function:
mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+
If you haven't selected any database yet, the result is blank.
To find out what tables the current database contains (for example, when you're not sure about the name of a table), use this command:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | event | | pet | +---------------------+
If you want to find out about the structure of a table, the
DESCRIBE command is useful; it displays information about each of a
table's columns:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
Field indicates the column name, Type is the data
type for the column, Null indicates whether or not the column can
contain NULL values, Key indicates whether or not the
column is indexed, and Default specifies the column's default
value.
If you have indexes on a table, SHOW INDEX FROM tbl_name
produces information about them.
Here are examples of how to solve some common problems with MySQL.
Some of the examples use the table shop to hold the price of
each article (item number) for certain traders (dealers). Supposing that each
trader has a single fixed price per article, then (article,
dealer) is a primary key for the records.
Start the command line tool mysql and select a database:
mysql your-database-name
(In most MySQL installations, you can use the database-name 'test').
You can create the example table as:
CREATE TABLE shop ( article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL, dealer CHAR(20) DEFAULT '' NOT NULL, price DOUBLE(16,2) DEFAULT '0.00' NOT NULL, PRIMARY KEY(article, dealer)); INSERT INTO shop VALUES (1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69), (3,'D',1.25),(4,'D',19.95);
Okay, so the example data is:
mysql> SELECT * FROM shop; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0001 | A | 3.45 | | 0001 | B | 3.99 | | 0002 | A | 10.99 | | 0003 | B | 1.45 | | 0003 | C | 1.69 | | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
``What's the highest item number?''
SELECT MAX(article) AS article FROM shop +---------+ | article | +---------+ | 4 | +---------+
``Find number, dealer, and price of the most expensive article.''
In ANSI SQL this is easily done with a sub-query:
SELECT article, dealer, price FROM shop WHERE price=(SELECT MAX(price) FROM shop)
In MySQL (which does not yet have sub-selects), just do it in two steps:
SELECT
statement.
SELECT article, dealer, price FROM shop WHERE price=19.95
Another solution is to sort all rows descending by price and only get the
first row using the MySQL specific LIMIT clause:
SELECT article, dealer, price FROM shop ORDER BY price DESC LIMIT 1
NOTE: If there are several most expensive articles (for
example, each 19.95) the LIMIT solution shows only one of them!
``What's the highest price per article?''
SELECT article, MAX(price) AS price FROM shop GROUP BY article +---------+-------+ | article | price | +---------+-------+ | 0001 | 3.99 | | 0002 | 10.99 | | 0003 | 1.69 | | 0004 | 19.95 | +---------+-------+
``For each article, find the dealer(s) with the most expensive price.''
In ANSI SQL, I'd do it with a sub-query like this:
SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);
In MySQL it's best do it in several steps:
This can easily be done with a temporary table:
CREATE TEMPORARY TABLE tmp (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL);
LOCK TABLES shop read;
INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;
SELECT shop.article, dealer, shop.price FROM shop, tmp
WHERE shop.article=tmp.article AND shop.price=tmp.price;
UNLOCK TABLES;
DROP TABLE tmp;
If you don't use a TEMPORARY table, you must also lock the 'tmp'
table.
``Can it be done with a single query?''
Yes, but only by using a quite inefficient trick that I call the ``MAX-CONCAT trick'':
SELECT article,
SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
FROM shop
GROUP BY article;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | C | 1.69 |
| 0004 | D | 19.95 |
+---------+--------+-------+
The last example can, of course, be made a bit more efficient by doing the splitting of the concatenated column in the client.
You can use MySQL user variables to remember results without having to store them in temporary variables in the client. See section 6.1.4 User Variables.
For example, to find the articles with the highest and lowest price you can do:
select @min_price:=min(price),@max_price:=max(price) from shop; select * from shop where price=@min_price or price=@max_price; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
In MySQL 3.23.44 and up, InnoDB tables supports checking of
foreign key constraints. See section 7.5 InnoDB
Tables. See also section 1.7.4.5
Foreign Keys.
You don't actually need foreign keys to join 2 tables. The only thing MySQL
currently doesn't do (in type types other than InnoDB), is
CHECK to make sure that the keys you use really exist in the
table(s) you're referencing and it doesn't automatically delete rows from a
table with a foreign key definition. If you use your keys like normal, it'll
work just fine:
CREATE TABLE person (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
name CHAR(60) NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE shirt (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
style ENUM('t-shirt', 'polo', 'dress') NOT NULL,
color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL,
owner SMALLINT UNSIGNED NOT NULL REFERENCES persons,
PRIMARY KEY (id)
);
INSERT INTO person VALUES (NULL, 'Antonio Paz');
INSERT INTO shirt VALUES
(NULL, 'polo', 'blue', LAST_INSERT_ID()),
(NULL, 'dress', 'white', LAST_INSERT_ID()),
(NULL, 't-shirt', 'blue', LAST_INSERT_ID());
INSERT INTO person VALUES (NULL, 'Lilliana Angelovska');
INSERT INTO shirt VALUES
(NULL, 'dress', 'orange', LAST_INSERT_ID()),
(NULL, 'polo', 'red', LAST_INSERT_ID()),
(NULL, 'dress', 'blue', LAST_INSERT_ID()),
(NULL, 't-shirt', 'white', LAST_INSERT_ID());
SELECT * FROM person;
+----+---------------------+
| id | name |
+----+---------------------+
| 1 | Antonio Paz |
| 2 | Lilliana Angelovska |
+----+---------------------+
SELECT * FROM shirt;
+----+---------+--------+-------+
| id | style | color | owner |
+----+---------+--------+-------+
| 1 | polo | blue | 1 |
| 2 | dress | white | 1 |
| 3 | t-shirt | blue | 1 |
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
| 7 | t-shirt | white | 2 |
+----+---------+--------+-------+
SELECT s.* FROM person p, shirt s
WHERE p.name LIKE 'Lilliana%'
AND s.owner = p.id
AND s.color <> 'white';
+----+-------+--------+-------+
| id | style | color | owner |
+----+-------+--------+-------+
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
+----+-------+--------+-------+
MySQL doesn't yet optimise when you search on two different keys combined
with OR (searching on one key with different OR parts
is optimised quite well):
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' OR field2_index = '1'
The reason is that we haven't yet had time to come up with an efficient way
to handle this in the general case. (The AND handling is, in
comparison, now completely general and works very well.)
For the moment you can solve this very efficiently by using a
TEMPORARY table. This type of optimisation is also very good if you
are using very complicated queries where the SQL server does the optimisations
in the wrong order.
CREATE TEMPORARY TABLE tmp SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'; INSERT INTO tmp SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1'; SELECT * from tmp; DROP TABLE tmp;
The above way to solve this query is in effect a UNION of two
queries. See section 6.4.1.2
UNION Syntax.
The following shows an idea of how you can use the bit group functions to calculate the number of days per month a user has visited a web page.
CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL, day INT(2) UNSIGNED ZEROFILL); INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2),(2000,2,23),(2000,2,23); SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1 GROUP BY year,month; Which returns: +------+-------+------+ | year | month | days | +------+-------+------+ | 2000 | 01 | 3 | | 2000 | 02 | 2 | +------+-------+------+
The above calculates how many different days was used for a given year/month combination, with automatic removal of duplicate entries.
The AUTO_INCREMENT attribute can be used to
generate an unique identity for new rows:
CREATE TABLE animals (id mediumint not null auto_increment,
name char(30) not null,
primary key (id));
INSERT INTO animals (name) values ("dog"),("cat"),("penguin"),("lax"),("whale");
SELECT * FROM animals;
Which returns:
+----+---------+
| id | name |
+----+---------+
| 1 | dog |
| 2 | cat |
| 3 | penguin |
| 4 | lax |
| 5 | whale |
+----+---------+
For MyISAM and BDB tables you can specify AUTO_INCREMENT on
secondary column in a multi-column key. In this case the generated value for the
autoincrement column is calculated as MAX(auto_increment_column)+1) WHERE
prefix=given-prefix. This is useful when you want to put data into
ordered groups.
CREATE TABLE animals (grp enum ('fish','mammal','bird') not null,
id mediumint not null auto_increment,
name char(30) not null,
primary key (grp,id));
INSERT INTO animals (grp,name) values ("mammal","dog"),("mammal","cat"),("bird","penguin"),("fish","lax"),("mammal","whale");
SELECT * FROM animals order by grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
+--------+----+---------+
Note that in this case, the auto_increment value will be reused if you delete the row with the biggest auto_increment value in any group.
You can get the used AUTO_INCREMENT key with the
LAST_INSERT_ID() SQL function or the mysql_insert_id()
API function.
mysql in Batch ModeIn the previous sections, you used mysql interactively to enter
queries and view the results. You can also run mysql in batch mode.
To do this, put the commands you want to run in a file, then tell
mysql to read its input from the file:
shell> mysql < batch-file
If you need to specify connection parameters on the command line, the command might look like this:
shell> mysql -h host -u user -p < batch-file Enter password: ********
When you use mysql this way, you are creating a script file,
then executing the script.
Why use a script? Here are a few reasons:
mysql to execute
it again.
shell> mysql < batch-file | more
shell> mysql < batch-file > mysql.out
cron job. In this case, you must use batch
mode. The default output format is different (more concise) when you run
mysql in batch mode than when you use it interactively. For
example, the output of SELECT DISTINCT species FROM pet looks like
this when run interactively:
+---------+ | species | +---------+ | bird | | cat | | dog | | hamster | | snake | +---------+
But like this when run in batch mode:
species bird cat dog hamster snake
If you want to get the interactive output format in batch mode, use
mysql -t. To echo to the output the commands that are executed, use
mysql -vvv.
At Analytikerna and Lentus, we have been doing the systems and field work for a big research project. This project is a collaboration between the Institute of Environmental Medicine at Karolinska Institutet Stockholm and the Section on Clinical Research in Aging and Psychology at the University of Southern California.
The project involves a screening part where all twins in Sweden older than 65 years are interviewed by telephone. Twins who meet certain criteria are passed on to the next stage. In this latter stage, twins who want to participate are visited by a doctor/nurse team. Some of the examinations include physical and neuropsychological examination, laboratory testing, neuroimaging, psychological status assessment, and family history collection. In addition, data are collected on medical and environmental risk factors.
More information about Twin studies can be found at: http://www.imm.ki.se/TWIN/TWINUKW.HTM
The latter part of the project is administered with a Web interface written using Perl and MySQL.
Each night all data from the interviews are moved into a MySQL database.
The following query is used to determine who goes into the second part of the project:
select
concat(p1.id, p1.tvab) + 0 as tvid,
concat(p1.christian_name, " ", p1.surname) as Name,
p1.postal_code as Code,
p1.city as City,
pg.abrev as Area,
if(td.participation = "Aborted", "A", " ") as A,
p1.dead as dead1,
l.event as event1,
td.suspect as tsuspect1,
id.suspect as isuspect1,
td.severe as tsevere1,
id.severe as isevere1,
p2.dead as dead2,
l2.event as event2,
h2.nurse as nurse2,
h2.doctor as doctor2,
td2.suspect as tsuspect2,
id2.suspect as isuspect2,
td2.severe as tsevere2,
id2.severe as isevere2,
l.finish_date
from
twin_project as tp
/* For Twin 1 */
left join twin_data as td on tp.id = td.id and tp.tvab = td.tvab
left join informant_data as id on tp.id = id.id and tp.tvab = id.tvab
left join harmony as h on tp.id = h.id and tp.tvab = h.tvab
left join lentus as l on tp.id = l.id and tp.tvab = l.tvab
/* For Twin 2 */
left join twin_data as td2 on p2.id = td2.id and p2.tvab = td2.tvab
left join informant_data as id2 on p2.id = id2.id and p2.tvab = id2.tvab
left join harmony as h2 on p2.id = h2.id and p2.tvab = h2.tvab
left join lentus as l2 on p2.id = l2.id and p2.tvab = l2.tvab,
person_data as p1,
person_data as p2,
postal_groups as pg
where
/* p1 gets main twin and p2 gets his/her twin. */
/* ptvab is a field inverted from tvab */
p1.id = tp.id and p1.tvab = tp.tvab and
p2.id = p1.id and p2.ptvab = p1.tvab and
/* Just the sceening survey */
tp.survey_no = 5 and
/* Skip if partner died before 65 but allow emigration (dead=9) */
(p2.dead = 0 or p2.dead = 9 or
(p2.dead = 1 and
(p2.death_date = 0 or
(((to_days(p2.death_date) - to_days(p2.birthday)) / 365)
>= 65))))
and
(
/* Twin is suspect */
(td.future_contact = 'Yes' and td.suspect = 2) or
/* Twin is suspect - Informant is Blessed */
(td.future_contact = 'Yes' and td.suspect = 1 and id.suspect = 1) or
/* No twin - Informant is Blessed */
(ISNULL(td.suspect) and id.suspect = 1 and id.future_contact = 'Yes') or
/* Twin broken off - Informant is Blessed */
(td.participation = 'Aborted'
and id.suspect = 1 and id.future_contact = 'Yes') or
/* Twin broken off - No inform - Have partner */
(td.participation = 'Aborted' and ISNULL(id.suspect) and p2.dead = 0))
and
l.event = 'Finished'
/* Get at area code */
and substring(p1.postal_code, 1, 2) = pg.code
/* Not already distributed */
and (h.nurse is NULL or h.nurse=00 or h.doctor=00)
/* Has not refused or been aborted */
and not (h.status = 'Refused' or h.status = 'Aborted'
or h.status = 'Died' or h.status = 'Other')
order by
tvid;
Some explanations:
concat(p1.id, p1.tvab) + 0 as tvid
id and tvab
in numerical order. Adding 0 to the result causes MySQL to treat
the result as a number.
id
tvab
1 or
2.
ptvab
tvab. When tvab is
1 this is 2, and vice versa. It exists to save
typing and to make it easier for MySQL to optimise the query. This query demonstrates, among other things, how to do lookups on a table
from the same table with a join (p1 and p2). In the
example, this is used to check whether a twin's partner died before the age of
65. If so, the row is not returned.
All of the above exist in all tables with twin-related information. We have a
key on both id,tvab (all tables), and id,ptvab
(person_data) to make queries faster.
On our production machine (A 200MHz UltraSPARC), this query returns about 150-200 rows and takes less than one second.
The current number of records in the tables used above:
| Table | Rows |
person_data |
71074 |
lentus |
5291 |
twin_project |
5286 |
twin_data |
2012 |
informant_data |
663 |
harmony |
381 |
postal_groups |
100 |
Each interview ends with a status code called event. The query
shown below is used to display a table over all twin pairs combined by event.
This indicates in how many pairs both twins are finished, in how many pairs one
twin is finished and the other refused, and so on.
select
t1.event,
t2.event,
count(*)
from
lentus as t1,
lentus as t2,
twin_project as tp
where
/* We are looking at one pair at a time */
t1.id = tp.id
and t1.tvab=tp.tvab
and t1.id = t2.id
/* Just the sceening survey */
and tp.survey_no = 5
/* This makes each pair only appear once */
and t1.tvab='1' and t2.tvab='2'
group by
t1.event, t2.event;
There are programs that let you authenticate your users from a MySQL database and also let you log your log files into a MySQL table. See section 1.6.1 MySQL Portals.
You can change the Apache logging format to be easily readable by MySQL by putting the following into the Apache configuration file:
LogFormat \
"\"%h\",%{%Y%m%d%H%M%S}t,%>s,\"%b\",\"%{Content-Type}o\", \
\"%U\",\"%{Referer}i\",\"%{User-Agent}i\""
In MySQL you can do something like this:
LOAD DATA INFILE '/local/access_log' INTO TABLE table_name FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' ESCAPED BY '\\'
In most cases you should manage mysqld options through option files. See section 4.1.2 my.cnf Option Files.
mysqld and mysqld.server reads options from the
mysqld and server groups. mysqld_safe
read options from the mysqld, server,
mysqld_safe and safe_mysqld groups. An embedded MySQL
server usually reads options from the server, embedded
and xxxxx_SERVER, where xxxxx is the name of the
application.
mysqld accepts the following command-line options:
--ansi
-b, --basedir=path
--big-tables
--bind-address=IP
--character-sets-dir=path
--chroot=path
mysqld daemon during startup. Recommended security
measure. It will somewhat limit LOAD DATA INFILE and SELECT
... INTO OUTFILE though.
--core-file
mysqld dies. For some systems you must
also specify --core-file-size to safe_mysqld. See
section 4.7.2
safe_mysqld, the wrapper around mysqld.
-h, --datadir=path
--debug[...]=
--with-debug, you can use this
option to get a trace file of what mysqld is doing. See section
E.1.2
Creating trace files.
--default-character-set=charset
--default-table-type=type
--delay-key-write-for-all-tables
MyISAM table.
See section 5.5.2
Tuning Server Parameters.
--des-key-file=filename
des_encrypt() and
des_decrypt() from this file.
--enable-locking
-T, --exit-info
--flush
-?, --help
--init-file=file
-L, --language=...
-l, --log[=file]
--log-isam[=file]
--log-slow-queries[=file]
long_query_time
seconds to execute to file. See section 4.9.5
The Slow Query Log.
--log-update[=file]
file.# where # is a unique number
if not given. See section 4.9.3
The Update Log.
--log-long-format
--log-slow-queries then queries that are not using indexes are
logged to the slow query log.
--low-priority-updates
INSERT/DELETE/UPDATE) will have lower
priority than selects. It can also be done via {INSERT | REPLACE |
UPDATE | DELETE} LOW_PRIORITY ... to lower the priority of only one
query, or by SET OPTION SQL_LOW_PRIORITY_UPDATES=1 to change the
priority in one thread. See section 5.3.2
Table Locking Issues.
--memlock
mysqld process in memory. This works only if your
system supports the mlockall() system call (like Solaris). This
may help if you have a problem where the operating system is causing
mysqld to swap on disk.
--myisam-recover [=option[,option...]]] where option is any
combination
DEFAULT, BACKUP, FORCE or
QUICK. You can also set this explicitely to "" if
you want to disable this option. If this option is used, mysqld
will on open check if the table is marked as crashed or if if the table wasn't
closed properly. (The last option only works if you are running with
--skip-locking.) If this is the case mysqld will run
check on the table. If the table was corrupted, mysqld will
attempt to repair it. The following options affects how the repair works.
| Option | Description |
| DEFAULT | The same as not giving any option to --myisam-recover.
|
| BACKUP | If the data table was changed during recover, save a backup of the `table_name.MYD' data file as `table_name-datetime.BAK'. |
| FORCE | Run recover even if we will loose more than one row from the .MYD file. |
| QUICK | Don't check the rows in the table if there isn't any delete blocks. |
BACKUP,FORCE. This will force a repair of a table even if some
rows would be deleted, but it will keep the old data file as a backup so that
you can later examine what happened.
--pid-file=path
safe_mysqld.
-P, --port=...
-o, --old-protocol
--one-thread
-O, --set-variable var=option
--help lists variables. You can find
a full description for all variables in the SHOW VARIABLES
section in this manual. See section 4.5.6.4
SHOW VARIABLES. The tuning server parameters section includes
information of how to optimise these. See section 5.5.2
Tuning Server Parameters.
--safe-mode
--skip-delay-key-write.
--safe-show-database
--safe-user-create
INSERT privilege to the
mysql.user table or any column in this table.
--skip-concurrent-insert
MyISAM tables. (This is only to be used if you think you have
found a bug in this feature.)
--skip-delay-key-write
delay_key_write option for all tables. See section
5.5.2
Tuning Server Parameters.
--skip-grant-tables
mysqladmin
flush-privileges or mysqladmin reload.)
--skip-host-cache
--skip-locking
isamchk or
myisamchk you must shut down the server. See section 1.2.3
How Stable Is MySQL?. Note that in MySQL Version 3.23 you can use
REPAIR and CHECK to repair/check MyISAM
tables.
--skip-name-resolve
Host column values in the
grant tables must be IP numbers or localhost. See section 5.5.5 How
MySQL uses DNS.
--skip-networking
mysqld must be made via Unix sockets. This option is highly
recommended for systems where only local requests are allowed. See section 5.5.5 How
MySQL uses DNS.
--skip-new
--skip-delay-key-write. This will also set default table type to
ISAM. See section 7.3 ISAM
Tables.
--skip-symlink
--skip-safemalloc
--with-debug=full, all programs
will check the memory for overruns for every memory allocation and memory
freeing. As this checking is very slow, you can avoid this, when you don't
need memory checking, by using this option.
--skip-show-database
--skip-stack-trace
mysqld under a debugger. See section E.1
Debugging a MySQL server.
--skip-thread-priority
--socket=path
/tmp/mysql.sock.
--sql-mode=option[,option[,option...]]
REAL_AS_FLOAT,
PIPES_AS_CONCAT, ANSI_QUOTES,
IGNORE_SPACE, SERIALIZE,
ONLY_FULL_GROUP_BY. It can also be empty ("") if you
want to reset this. By specifying all of the above options is same as using
--ansi. With this option one can turn on only needed SQL modes. See section 1.7.2
Running MySQL in ANSI Mode.
transaction-isolation= { READ-UNCOMMITTED | READ-COMMITTED |
REPEATABLE-READ | SERIALIZABLE }
SET TRANSACTION Syntax.
-t, --tmpdir=path
/tmp directory resides on a partition too small to hold temporary
tables.
-u, --user=user_name
mysqld daemon as user user_name. This option
is mandatory when starting mysqld as root.
-V, --version
-W, --warnings
Aborted connection... to the
.err file. See section A.2.9
Communication Errors / Aborted Connection. MySQL can, since Version 3.22, read default startup options for the server and for clients from option files.
MySQL reads default options from the following files on Unix:
| Filename | Purpose |
/etc/my.cnf |
Global options |
DATADIR/my.cnf |
Server-specific options |
defaults-extra-file |
The file specified with --defaults-extra-file=# |
~/.my.cnf |
User-specific options |
DATADIR is the MySQL data directory (typically
`/usr/local/mysql/data' for a binary installation or
`/usr/local/var' for a source installation). Note that this is the
directory that was specified at configuration time, not the one specified with
--datadir when mysqld starts up!
(--datadir has no effect on where the server looks for option
files, because it looks for them before it processes any command-line
arguments.)
MySQL reads default options from the following files on Windows:
| Filename | Purpose |
windows-system-directory\my.ini |
Global options |
C:\my.cnf |
Global options |
C:\mysql\data\my.cnf |
Server-specific options |
Note that on Windows, you should specify all paths with /
instead of \. If you use \, you need to specify this
twice, as \ is the escape character in MySQL.
MySQL tries to read option files in the order listed above. If multiple option files exist, an option specified in a file read later takes precedence over the same option specified in a file read earlier. Options specified on the command line take precedence over options specified in any option file. Some options can be specified using environment variables. Options specified on the command line or in option files take precedence over environment variable values. See section F Environment Variables.
The following programs support option files: mysql,
mysqladmin, mysqld, mysqld_safe,
mysql.server, mysqldump, mysqlimport,
mysqlshow, mysqlcheck, myisamchk, and
myisampack.
Any long option that may be given on the command line when running a MySQL
program can be given in an option file as well (without the leading double
dash). Run the program with --help to get a list of available
options.
An option file can contain lines of the following forms:
#comment
[group]
group is the name of the program or group for which you want
to set options. After a group line, any option or
set-variable lines apply to the named group until the end of the
option file or another group line is given.
option
--option on the command line.
option=value
--option=value on the command line.
set-variable = variable=value
--set-variable variable=value on the
command line. This syntax must be used to set a mysqld variable.
The client group allows you to specify options that apply to all
MySQL clients (not mysqld). This is the perfect group to use to
specify the password you use to connect to the server. (But make sure the option
file is readable and writable only by yourself.)
Note that for options and values, all leading and trailing blanks are automatically deleted. You may use the escape sequences `\b', `\t', `\n', `\r', `\\', and `\s' in your value string (`\s' == blank).
Here is a typical global option file:
[client] port=3306 socket=/tmp/mysql.sock [mysqld] port=3306 socket=/tmp/mysql.sock set-variable = key_buffer_size=16M set-variable = max_allowed_packet=1M [mysqldump] quick
Here is typical user option file:
[client] # The following password will be sent to all standard MySQL clients password=my_password [mysql] no-auto-rehash set-variable = connect_timeout=2 [mysqlhotcopy] interactive-timeout
If you have a source distribution, you will find sample
configuration files named `my-xxxx.cnf' in the `support-files'
directory. If you have a binary distribution, look in the
`DIR/support-files' directory, where DIR is the pathname
to the MySQL installation directory (typically `/usr/local/mysql').
Currently there are sample configuration files for small, medium, large, and
very large systems. You can copy `my-xxxx.cnf' to your home directory
(rename the copy to `.my.cnf') to experiment with this.
All MySQL clients that support option files support the following options:
| Option | Description |
| --no-defaults | Don't read any option files. |
| --print-defaults | Print the program name and all options that it will get. |
| --defaults-file=full-path-to-default-file | Only use the given configuration file. |
| --defaults-extra-file=full-path-to-default-file | Read this configuration file after the global configuration file but before the user configuration file. |
Note that the above options must be first on the command line to work!
--print-defaults may however be used directly after the
--defaults-xxx-file commands.
Note for developers: Option file handling is implemented simply by processing all matching options (that is, options in the appropriate group) before any command-line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have an old program that handles multiply-specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard MySQL clients to see how to do this.
In shell scripts you can use the `my_print_defaults' command to parse the config files:
shell> my_print_defaults client mysql --port=3306 --socket=/tmp/mysql.sock --no-auto-rehash
The above output contains all options for the groups 'client' and 'mysql'.
In some cases you may want to have many different mysqld daemons
(servers) running on the same machine. You may for example want to run a new
version of MySQL for testing together with an old version that is in production.
Another case is when you want to give different users access to different
mysqld servers that they manage themselves.
One way to get a new server running is by starting it with a different socket and port as follows:
shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock shell> MYSQL_TCP_PORT=3307 shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT shell> scripts/mysql_install_db shell> bin/safe_mysqld &
The environment variables appendix includes a list of other environment
variables you can use to affect mysqld. See section F
Environment Variables.
The above is the quick and dirty way that one commonly uses for testing. The nice thing with this is that all connections you do in the above shell will automatically be directed to the new running server!
If you need to do this more permanently, you should create an option file for each server. See section 4.1.2 my.cnf Option Files. In your startup script that is executed at boot time (mysql.server?) you should specify for both servers:
safe_mysqld --default-file=path-to-option-file
At least the following options should be different per server:
The following options should be different, if they are used:
If you want more performance, you can also specify the following differently:
See section 4.1.1 mysqld Command-line Options.
If you are installing binary MySQL versions (.tar files) and start them with
./bin/safe_mysqld then in most cases the only option you need to
add/change is the socket and port argument to
safe_mysqld.
See section 4.1.4 Running Multiple MySQL Servers on the Same Machine.
There are circumstances when you might want to run multiple servers on the same machine. For example, you might want to test a new MySQL release while leaving your existing production setup undisturbed. Or you might be an Internet service provider that wants to provide independent MySQL installations for different customers.
If you want to run multiple servers, the easiest way is to compile the servers with different TCP/IP ports and socket files so they are not both listening to the same TCP/IP port or socket file. See section 4.7.3 mysqld_multi, program for managing multiple MySQL servers.
Assume an existing server is configured for the default port number and
socket file. Then configure the new server with a configure command
something like this:
shell> ./configure --with-tcp-port=port_number \
--with-unix-socket-path=file_name \
--prefix=/usr/local/mysql-3.22.9
Here port_number and file_name should be different
than the default port number and socket file pathname, and the
--prefix value should specify an installation directory different
than the one under which the existing MySQL installation is located.
You can check the socket used by any currently executing MySQL server with this command:
shell> mysqladmin -h hostname --port=port_number variables
Note that if you specify ``localhost'' as a hostname,
mysqladmin will default to using Unix sockets instead of TCP/IP.
If you have a MySQL server running on the port you used, you will get a list of some of the most important configurable variables in MySQL, including the socket name.
You don't have to recompile a new MySQL server just to start with a different
port and socket. You can change the port and socket to be used by specifying
them at run time as options to safe_mysqld:
shell> /path/to/safe_mysqld --socket=file_name --port=port_number
mysqld_multi can also take safe_mysqld (or
mysqld) as an argument and pass the options from a configuration
file to safe_mysqld and further to mysqld.
If you run the new server on the same database directory as another server
with logging enabled, you should also specify the name of the log files to
safe_mysqld with --log, --log-update, or
--log-slow-queries. Otherwise, both servers may be trying to write
to the same log file.
Warning: Normally you should never have two servers that update data in the same database! If your OS doesn't support fault-free system locking, this may lead to unpleasant surprises!
If you want to use another database directory for the second server, you can
use the --datadir=path option to safe_mysqld.
Note also that starting several MySQL servers
(mysqlds) in different machines and letting them access one data
directory over NFS is generally a bad idea! The
problem is that the NFS will become the bottleneck with the speed.
It is not meant for such use. And last but not least, you would still have to
come up with a solution how to make sure that two or more mysqlds
are not interfering with each other. At the moment there is no platform that
would 100% reliable do the file locking (lockd daemon usually) in
every situation. Yet there would be one more possible risk with
NFS; it would make the work even more complicated for
lockd daemon to handle. So make it easy for your self and forget
about the idea. The working solution is to have one computer with an operating
system that efficiently handles threads and have several CPUs in it.
When you want to connect to a MySQL server that is running with a different port than the port that is compiled into your client, you can use one of the following methods:
--host 'hostname' --port=port_number to
connect with TCP/IP, or [--host localhost] --socket=file_name to
connect via a Unix socket.
DBD::mysql module you can read the
options from the MySQL option files. See section 4.1.2
my.cnf Option Files. $dsn = "DBI:mysql:test;mysql_read_default_group=client;mysql_read_default_file=/usr/local/mysql/data/my.cnf" $dbh = DBI->connect($dsn, $user, $password);
MYSQL_UNIX_PORT and
MYSQL_TCP_PORT environment variables to point to the Unix socket
and TCP/IP port before you start your clients. If you normally use a specific
socket or port, you should place commands to set these environment variables
in your `.login' file. See section F
Environment Variables.
MySQL has an advanced but non-standard security/privilege system. This section describes how it works.
Anyone using MySQL on a computer connected to the Internet should read this section to avoid the most common security mistakes.
In discussing security, we emphasize the necessity of fully protecting the entire server host (not simply the MySQL server) against all types of applicable attacks: eavesdropping, altering, playback, and denial of service. We do not cover all aspects of availability and fault tolerance here.
MySQL uses security based on Access Control Lists (ACLs) for all connections, queries, and other operations that a user may attempt to perform. There is also some support for SSL-encrypted connections between MySQL clients and servers. Many of the concepts discussed here are not specific to MySQL at all; the same general ideas apply to almost all applications.
When running MySQL, follow these guidelines whenever possible:
user table in the mysql database! This is
critical. The encrypted password is the real password in
MySQL. Anyone who knows the password which is listed in the
user table and has access to the host listed for the account
can easily log in as that user.
GRANT and
REVOKE commands are used for controlling access to MySQL. Do not
grant any more privileges than necessary. Never grant privileges to all hosts.
Checklist:
mysql -u root. If you are able to connect successfully
to the server without being asked for a password, you have problems. Anyone
can connect to your MySQL server as the MySQL root user with
full privileges! Review the MySQL installation instructions, paying
particular attention to the item about setting a root password.
SHOW GRANTS and check to see who has access
to what. Remove those privileges that are not necessary using the
REVOKE command. MD5() or another one-way hashing function.
nmap. MySQL uses port 3306 by default. This port should be
inaccessible from untrusted hosts. Another simple way to check whether or
not your MySQL port is open is to try the following command from some remote
machine, where server_host is the hostname of your MySQL
server: shell> telnet server_host 3306If you get a connection and some garbage characters, the port is open, and should be closed on your firewall or router, unless you really have a good reason to keep it open. If
telnet just hangs or the
connection is refused, everything is OK; the port is blocked. ; DROP DATABASE
mysql;''. This is an extreme example, but large security leaks and data
loss may occur as a result of hackers using similar techniques, if you do not
prepare for them. Also remember to check numeric data. A common mistake is to
protect only strings. Sometimes people think that if a database contains only
publicly available data that it need not be protected. This is incorrect. At
least denial-of-service type attacks can be performed on such databases. The
simplest way to protect from this type of attack is to use apostrophes around
the numeric constants: SELECT * FROM table WHERE ID='234' rather
than SELECT * FROM table WHERE ID=234. MySQL automatically
converts this string to a number and strips all non-numeric symbols from it.
Checklist:
%22
(`"'), %23 (`#'), and
%27 (`'') in the URL.
addslashes() function. As of PHP 4.0.3, a
mysql_escape_string() function is available that is based on
the function of the same name in the MySQL C API. mysql_escape_string() API call. escape and quote modifiers for
query streams. quote() method or use placeholders.
PreparedStatement object and placeholders.
tcpdump and strings utilities.
For most cases, you can check whether or not MySQL data streams are
unencrypted by issuing a command like the following: shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings(This works under Linux and should work with small modifications under other systems.) Warning: If you do not see data this doesn't always actually mean that it is encrypted. If you need high security, you should consult with a security expert.
When you connect to a MySQL server, you normally should use a password. The password is not transmitted in clear text over the connection, however the encryption algorithm is not very strong, and with some effort a clever attacker can crack the password if he is able to sniff the traffic between the client and the server. If the connection between the client and the server goes through an untrusted network, you should use an SSH tunnel to encrypt the communication.
All other information is transferred as text that can be read by anyone who
is able to watch the connection. If you are concerned about this, you can use
the compressed protocol (in MySQL Version 3.22 and above) to make things much
harder. To make things even more secure you should use ssh. You can
find an Open Source ssh client at http://www.openssh.org/, and a commercial
ssh client at http://www.ssh.com/. With this, you can get an
encrypted TCP/IP connection between a MySQL server and a MySQL client.
If you are using MySQL 4.0, you can also use internal openssl support. See section 4.3.8 Using Secure Connections.
To make a MySQL system secure, you should strongly consider the following suggestions:
mysql -u other_user db_name if
other_user has no password. It is common behavior with
client/server applications that the client may specify any user name. You can
change the password of all users by editing the mysql_install_db
script before you run it, or only the password for the MySQL root
user like this: shell> mysql -u root mysql
mysql> UPDATE user SET Password=PASSWORD('new_password') WHERE user='root';
mysql> FLUSH PRIVILEGES;
root user. This is
very dangerous, because any user with FILE privileges will be
able to create files as root (for example,
~root/.bashrc). To prevent this, mysqld will refuse
to run as root unless it is specified directly using a
--user=root option. mysqld can be run as an ordinary
unprivileged user instead. You can also create a new Unix user
mysql to make everything even more secure. If you run
mysqld as another Unix user, you don't need to change the
root user name in the user table, because MySQL user
names have nothing to do with Unix user names. To start mysqld as
another Unix user, add a user line that specifies the user name
to the [mysqld] group of the `/etc/my.cnf' option file
or the `my.cnf' option file in the server's data directory. For
example: [mysqld] user=mysqlThis will cause the server to start as the designated user whether you start it manually or by using
safe_mysqld or
mysql.server. For more details, see section A.3.2
How to Run MySQL As a Normal User.
--skip-symlink option). This is especially important if you run
mysqld as root as anyone that has write access to the mysqld data
directories could then delete any file in the system! See section 5.6.1.2
Using Symbolic Links for Tables.
mysqld runs as is the only user
with read/write privileges in the database directories.
mysqladmin processlist shows the text of the currently
executing queries, so any user who is allowed to execute that command might be
able to see if another user issues an UPDATE user SET
password=PASSWORD('not_secure') query. mysqld reserves an
extra connection for users who have the process privilege, so
that a MySQL root user can log in and check things even if all
normal connections are in use.
mysqld daemon! To make this a bit safer, all
files generated with SELECT ... INTO OUTFILE are readable to
everyone, and you cannot overwrite existing files. The
file privilege may also be used to read any file accessible
to the Unix user that the server runs as. This could be abused, for example,
by using LOAD DATA to load `/etc/passwd' into a table,
which can then be read with SELECT.
max_user_connections variable in
mysqld. mysqld Concerning
SecurityThe following mysqld options affect security:
--safe-show-database
SHOW DATABASES returns only those databases
for which the user has some kind of privilege.
--safe-user-create
GRANT command, if the user doesn't have INSERT
privilege to the mysql.user table. If you want to give a user
access to just create new users with those privileges that the user has right
to grant, you should give the user the following privilege: GRANT INSERT(user) on mysql.user to 'user'@'hostname';This will ensure that the user can't change any privilege columns directly, but has to use the
GRANT command to give privileges to
other users.
--skip-grant-tables
mysqladmin
flush-privileges or mysqladmin reload.)
--skip-name-resolve
Host column values in the
grant tables must be IP numbers or localhost.
--skip-networking
mysqld must be made via Unix sockets. This option is unsuitable
for systems that use MIT-pthreads, because the MIT-pthreads package doesn't
support Unix sockets.
--skip-show-database
SHOW DATABASES statement doesn't return
anything. The primary function of the MySQL privilege system is to authenticate a user connecting from a given host, and to associate that user with privileges on a database such as select, insert, update and delete.
Additional functionality includes the ability to have an anonymous user and
to grant privileges for MySQL-specific functions such as LOAD DATA
INFILE and administrative operations.
The MySQL privilege system ensures that all users may do exactly the things that they are supposed to be allowed to do. When you connect to a MySQL server, your identity is determined by the host from which you connect and the user name you specify. The system grants privileges according to your identity and what you want to do.
MySQL considers both your hostname and user name in identifying you because
there is little reason to assume that a given user name belongs to the same
person everywhere on the Internet. For example, the user joe who
connects from office.com need not be the same person as the user
joe who connects from elsewhere.com. MySQL handles
this by allowing you to distinguish users on different hosts that happen to have
the same name: you can grant joe one set of privileges for
connections from office.com, and a different set of privileges for
connections from elsewhere.com.
MySQL access control involves two stages:
The server uses the user, db, and host
tables in the mysql database at both stages of access control. The
fields in these grant tables are shown below:
| Table name | user |
db |
host |
| Scope fields | Host |
Host |
Host |
User |
Db |
Db | |
Password |
User |
||
| Privilege fields | Select_priv |
Select_priv |
Select_priv |
Insert_priv |
Insert_priv |
Insert_priv | |
Update_priv |
Update_priv |
Update_priv | |
Delete_priv |
Delete_priv |
Delete_priv | |
Index_priv |
Index_priv |
Index_priv | |
Alter_priv |
Alter_priv |
Alter_priv | |
Create_priv |
Create_priv |
Create_priv | |
Drop_priv |
Drop_priv |
Drop_priv | |
Grant_priv |
Grant_priv |
Grant_priv | |
References_priv |
|||
Reload_priv |
|||
Shutdown_priv |
|||
Process_priv |
|||
File_priv |
For the second stage of access control (request verification), the server
may, if the request involves tables, additionally consult the
tables_priv and columns_priv tables. The fields in
these tables are shown below:
| Table name | tables_priv |
columns_priv |
| Scope fields | Host |
Host |
Db |
Db | |
User |
User | |
Table_name |
Table_name | |
Column_name | ||
| Privilege fields | Table_priv |
Column_priv |
Column_priv |
||
| Other fields | Timestamp |
Timestamp |
Grantor |
Each grant table contains scope fields and privilege fields.
Scope fields determine the scope of each entry in the tables, that is, the
context in which the entry applies. For example, a user table entry
with Host and User values of
'thomas.loc.gov' and 'bob' would be used for
authenticating connections made to the server by bob from the host
thomas.loc.gov. Similarly, a db table entry with
Host, User, and Db fields of
'thomas.loc.gov', 'bob' and 'reports'
would be used when bob connects from the host
thomas.loc.gov to access the reports database. The
tables_priv and columns_priv tables contain scope
fields indicating tables or table/column combinations to which each entry
applies.
For access-checking purposes, comparisons of
Host values are case insensitive. User,
Password, Db, and Table_name values are
case sensitive. Column_name values are case insensitive in MySQL
Version 3.22.12 or later.
Privilege fields indicate the privileges granted by a table entry, that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in section 4.2.9 Access Control, Stage 2: Request Verification.
Scope fields are strings, declared as shown below; the default value for each is the empty string:
| Field name | Type | Notes |
Host |
CHAR(60) |
|
User |
CHAR(16) |
|
Password |
CHAR(16) |
|
Db |
CHAR(64) |
(CHAR(60) for the tables_priv and
columns_priv tables) |
Table_name |
CHAR(60) |
|
Column_name |
CHAR(60) |
In the user, db and host tables, all
privilege fields are declared as ENUM('N','Y') -- each can have a
value of 'N' or 'Y', and the default value is
'N'.
In the tables_priv and columns_priv tables, the
privilege fields are declared as SET fields:
| Table name | Field name | Possible set elements |
tables_priv |
Table_priv |
'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop',
'Grant', 'References', 'Index', 'Alter' |
tables_priv |
Column_priv |
'Select', 'Insert', 'Update', 'References' |
columns_priv |
Column_priv |
'Select', 'Insert', 'Update', 'References'
|
Briefly, the server uses the grant tables like this:
user table scope fields determine whether to allow or
reject incoming connections. For allowed connections, any privileges granted
in the user table indicate the user's global (superuser)
privileges. These privileges apply to all databases on the
server.
db and host tables are used together:
db table scope fields determine which users can access
which databases from which hosts. The privilege fields determine which
operations are allowed.
host table is used as an extension of the
db table when you want a given db table entry to
apply to several hosts. For example, if you want a user to be able to use a
database from several hosts in your network, leave the Host
value empty in the user's db table entry, then populate the
host table with an entry for each of those hosts. This
mechanism is described more detail in section 4.2.9
Access Control, Stage 2: Request Verification. tables_priv and columns_priv tables are
similar to the db table, but are more fine-grained: they apply at
the table and column levels rather than at the database level. Note that administrative privileges (reload,
shutdown, etc.) are specified only in the user
table. This is because administrative operations are operations on the server
itself and are not database-specific, so there is no reason to list such
privileges in the other grant tables. In fact, only the user table
need be consulted to determine whether or not you can perform an administrative
operation.
The file privilege is specified only in the
user table, too. It is not an administrative privilege as such, but
your ability to read or write files on the server host is independent of the
database you are accessing.
The mysqld server reads the contents of the grant tables once,
when it starts up. Changes to the grant tables take effect as indicated in
section 4.3.3
When Privilege Changes Take Effect.
When you modify the contents of the grant tables, it is a good idea to make
sure that your changes set up privileges the way you want. For help in
diagnosing problems, see section 4.2.10
Causes of Access denied Errors. For advice on security issues,
see section 4.2.2 How
to Make MySQL Secure Against Crackers.
A useful diagnostic tool is the mysqlaccess script, which Yves
Carlier has provided for the MySQL distribution. Invoke mysqlaccess
with the --help option to find out how it works. Note that
mysqlaccess checks access using only the user,
db and host tables. It does not check table- or
column-level privileges.
Information about user privileges is stored in the user,
db, host, tables_priv, and
columns_priv tables in the mysql database (that is, in
the database named mysql). The MySQL server reads the contents of
these tables when it starts up and under the circumstances indicated in section
4.3.3
When Privilege Changes Take Effect.
The names used in this manual to refer to the privileges provided by MySQL are shown below, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies:
| Privilege | Column | Context |
| select | Select_priv |
tables |
| insert | Insert_priv |
tables |
| update | Update_priv |
tables |
| delete | Delete_priv |
tables |
| index | Index_priv |
tables |
| alter | Alter_priv |
tables |
| create | Create_priv |
databases, tables, or indexes |
| drop | Drop_priv |
databases or tables |
| grant | Grant_priv |
databases or tables |
| references | References_priv |
databases or tables |
| reload | Reload_priv |
server administration |
| shutdown | Shutdown_priv |
server administration |
| process | Process_priv |
server administration |
| file | File_priv |
file access on server |
The select, insert, update, and delete privileges allow you to perform operations on rows in existing tables in a database.
SELECT statements require the select privilege
only if they actually retrieve rows from a table. You can execute certain
SELECT statements even without permission to access any of the
databases on the server. For example, you could use the mysql
client as a simple calculator:
mysql> SELECT 1+1; mysql> SELECT PI()*2;
The index privilege allows you to create or drop (remove) indexes.
The alter privilege allows you to use ALTER
TABLE.
The create and drop privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables.
Note that if you grant the drop privilege for the
mysql database to a user, that user can drop the database in which
the MySQL access privileges are stored!
The grant privilege allows you to give to other users those privileges you yourself possess.
The file privilege gives you permission to read and write
files on the server using the LOAD DATA INFILE and SELECT ...
INTO OUTFILE statements. Any user to whom this privilege is granted can
read or write any file that the MySQL server can read or write.
The remaining privileges are used for administrative operations, which are
performed using the mysqladmin program. The table below shows which
mysqladmin commands each administrative privilege allows you to
execute:
| Privilege | Commands permitted to privilege holders |
| reload | reload, refresh,
flush-privileges, flush-hosts,
flush-logs, and flush-tables |
| shutdown | shutdown |
| process | processlist, kill |
The reload command tells the server to re-read the grant tables.
The refresh command flushes all tables and opens and closes the log
files. flush-privileges is a synonym for reload. The
other flush-* commands perform functions similar to
refresh but are more limited in scope, and may be preferable in
some instances. For example, if you want to flush just the log files,
flush-logs is a better choice than refresh.
The shutdown command shuts down the server.
The processlist command displays information about the threads
executing within the server. The kill command kills server threads.
You can always display or kill your own threads, but you need the
process privilege to display or kill threads initiated by other
users. See section 4.5.5
KILL Syntax.
It is a good idea in general to grant privileges only to those users who need them, but you should exercise particular caution in granting certain privileges:
SELECT. This includes the contents of
all databases hosted by the server!
mysql database can be used to change
passwords and other access privilege information. (Passwords are stored
encrypted, so a malicious user cannot simply read them to know the plain text
password.) If they can access the mysql.user password column,
they can use it to log into the MySQL server for the given user. (With
sufficient privileges, the same user can replace a password with a different
one.) There are some things that you cannot do with the MySQL privilege system:
MySQL client programs generally require that you specify connection
parameters when you want to access a MySQL server: the host you want to connect
to, your user name, and your password. For example, the mysql
client can be started like this (optional arguments are enclosed between
`[' and `]'):
shell> mysql [-h host_name] [-u user_name] [-pyour_pass]
Alternate forms of the -h, -u, and -p
options are --host=host_name, --user=user_name, and
--password=your_pass. Note that there is no space between
-p or --password= and the password following it.
Note: Specifying a password on the command line is not
secure! Any user on your system may then find out your password by typing a
command like: ps auxww. See section 4.1.2
my.cnf Option Files.
mysql uses default values for connection parameters that are
missing from the command line:
localhost.
-p is missing. Thus, for a Unix user joe, the following commands are
equivalent:
shell> mysql -h localhost -u joe shell> mysql -h localhost shell> mysql -u joe shell> mysql
Other MySQL clients behave similarly.
On Unix systems, you can specify different default values to be used when you make a connection, so that you need not enter them on the command line each time you invoke a client program. This can be done in a couple of ways:
[client] section of the `.my.cnf' configuration file in
your home directory. The relevant section of the file might look like this: [client] host=host_name user=user_name password=your_passSee section 4.1.2 my.cnf Option Files.
mysql using MYSQL_HOST. The MySQL user name can
be specified using USER (this is for Windows only). The password
can be specified using MYSQL_PWD (but this is insecure; see the
next section). See section F
Environment Variables. When you attempt to connect to a MySQL server, the server accepts or rejects the connection based on your identity and whether or not you can verify your identity by supplying the correct password. If not, the server denies access to you completely. Otherwise, the server accepts the connection, then enters Stage 2 and waits for requests.
Your identity is based on two pieces of information:
Identity checking is performed using the three user table scope
fields (Host, User, and Password). The
server accepts the connection only if a user table entry matches
your hostname and user name, and you supply the correct password.
Values in the user table scope fields may be specified as
follows:
Host value may be a hostname or an IP number, or
'localhost' to indicate the local host.
Host field.
Host value of '%' matches any hostname.
Host value means that the privilege should be anded
with the entry in the host table that matches the given host
name. You can find more information about this in the next chapter.
Host values specified as IP
numbers, you can specify a netmask indicating how many address bits to use for
the network number. For example: GRANT ALL PRIVILEGES on db.* to david@'192.58.197.0/255.255.255.0';This will allow everyone to connect from an IP where the following is true:
user_ip & netmask = host_ip.In the above example all IP:s in the interval 192.58.197.0 - 192.58.197.255 can connect to the MySQL server.
User field, but you can specify a blank value, which matches any
name. If the user table entry that matches an incoming connection
has a blank user name, the user is considered to be the anonymous user (the
user with no name), rather than the name that the client actually specified.
This means that a blank user name is used for all further access checking for
the duration of the connection (that is, during Stage 2).
Password field can be blank. This does not mean that any
password matches, it means the user must connect without specifying a
password. Non-blank Password values represent encrypted
passwords. MySQL does not store passwords in plaintext form for anyone to see.
Rather, the password supplied by a user who is attempting to connect is
encrypted (using the PASSWORD() function). The encrypted password
is then used when the client/server is checking if the password is correct.
(This is done without the encrypted password ever traveling over the
connection.) Note that from MySQL's point of view the encrypted password is the
REAL password, so you should not give anyone access to it! In particular, don't
give normal users read access to the tables in the mysql database!
The examples below show how various combinations of Host and
User values in user table entries apply to incoming
connections:
Host value |
User value |
Connections matched by entry |
'thomas.loc.gov' |
'fred' |
fred, connecting from thomas.loc.gov |
'thomas.loc.gov' |
'' |
Any user, connecting from thomas.loc.gov |
'%' |
'fred' |
fred, connecting from any host |
'%' |
'' |
Any user, connecting from any host |
'%.loc.gov' |
'fred' |
fred, connecting from any host in the
loc.gov domain |
'x.y.%' |
'fred' |
fred, connecting from x.y.net,
x.y.com,x.y.edu, etc. (this is probably not
useful) |
'144.155.166.177' |
'fred' |
fred, connecting from the host with IP address
144.155.166.177 |
'144.155.166.%' |
'fred' |
fred, connecting from any host in the
144.155.166 class C subnet |
'144.155.166.0/255.255.255.0' |
'fred' |
Same as previous example |
Because you can use IP wild-card values in the Host field (for
example, '144.155.166.%' to match every host on a subnet), there is
the possibility that someone might try to exploit this capability by naming a
host 144.155.166.somewhere.com. To foil such attempts, MySQL
disallows matching on hostnames that start with digits and a dot. Thus, if you
have a host named something like 1.2.foo.com, its name will never
match the Host column of the grant tables. Only an IP number can
match an IP wild-card value.
An incoming connection may be matched by more than one entry in the
user table. For example, a connection from
thomas.loc.gov by fred would be matched by several of
the entries just shown above. How does the server choose which entry to use if
more than one matches? The server resolves this question by sorting the
user table after reading it at startup time, then looking through
the entries in sorted order when a user attempts to connect. The first matching
entry is the one that is used.
user table sorting works as follows. Suppose the
user table looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | % | root | ... | % | jeffrey | ... | localhost | root | ... | localhost | | ... +-----------+----------+-
When the server reads in the table, it orders the entries with the
most-specific Host values first ('%' in the
Host column means ``any host'' and is least specific). Entries with
the same Host value are ordered with the most-specific
User values first (a blank User value means ``any
user'' and is least specific). The resulting sorted user table
looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | localhost | root | ... | localhost | | ... | % | jeffrey | ... | % | root | ... +-----------+----------+-
When a connection is
attempted, the server looks through the sorted entries and uses the first match
found. For a connection from localhost by jeffrey, the
entries with 'localhost' in the Host column match
first. Of those, the entry with the blank user name matches both the connecting
hostname and user name. (The '%'/'jeffrey' entry would have
matched, too, but it is not the first match in the table.)
Here is another example. Suppose the user table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | % | jeffrey | ... | thomas.loc.gov | | ... +----------------+----------+-
The sorted table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | thomas.loc.gov | | ... | % | jeffrey | ... +----------------+----------+-
A connection from thomas.loc.gov by jeffrey is
matched by the first entry, whereas a connection from
whitehouse.gov by jeffrey is matched by the second.
A common misconception is to think that for a given user name, all entries
that explicitly name that user will be used first when the server attempts to
find a match for the connection. This is simply not true. The previous example
illustrates this, where a connection from thomas.loc.gov by
jeffrey is first matched not by the entry containing
'jeffrey' as the User field value, but by the entry
with no user name!
If you have problems connecting to the server, print out the
user table and sort it by hand to see where the first match is
being made.
Once you establish a connection, the server enters Stage 2. For each request
that comes in on the connection, the server checks whether you have sufficient
privileges to perform it, based on the type of operation you wish to perform.
This is where the privilege fields in the grant tables come into play. These
privileges can come from any of the user, db,
host, tables_priv, or columns_priv
tables. The grant tables are manipulated with GRANT and
REVOKE commands. See section 4.3.1
GRANT and REVOKE Syntax. (You may find it helpful
to refer to section 4.2.5
How the Privilege System Works, which lists the fields present in each of
the grant tables.)
The user table grants privileges that are assigned to you on a
global basis and that apply no matter what the current database is. For example,
if the user table grants you the delete privilege,
you can delete rows from any database on the server host! In other words,
user table privileges are superuser privileges. It is wise to grant
privileges in the user table only to superusers such as server or
database administrators. For other users, you should leave the privileges in the
user table set to 'N' and grant privileges on a
database-specific basis only, using the db and host
tables.
The db
and host tables grant database-specific privileges. Values in the
scope fields may be specified as follows:
Host and Db fields of either table.
'%' Host value in the db table
means ``any host.'' A blank Host value in the db
table means ``consult the host table for further information.''
'%' or blank Host value in the
host table means ``any host.''
'%' or blank Db value in either table means
``any database.''
User value in either table matches the anonymous
user. The db and host tables are read in and
sorted when the server starts up (at the same time that it reads the
user table). The db table is sorted on the
Host, Db, and User scope fields, and the
host table is sorted on the Host and Db
scope fields. As with the user table, sorting puts the
most-specific values first and least-specific values last, and when the server
looks for matching entries, it uses the first match that it finds.
The tables_priv and
columns_priv tables grant table- and column-specific privileges.
Values in the scope fields may be specified as follows:
Host field of either table.
'%' or blank Host value in either table means
``any host.''
Db, Table_name and Column_name
fields cannot contain wild cards or be blank in either table. The tables_priv and columns_priv tables are sorted
on the Host, Db, and User fields. This is
similar to db table sorting, although the sorting is simpler
because only the Host field may contain wild cards.
The request verification process is described below. (If you are familiar with the access-checking source code, you will notice that the description here differs slightly from the algorithm used in the code. The description is equivalent to what the code actually does; it differs only to make the explanation simpler.)
For administrative requests (shutdown,
reload, etc.), the server checks only the user
table entry, because that is the only table that specifies administrative
privileges. Access is granted if the entry allows the requested operation and
denied otherwise. For example, if you want to execute mysqladmin
shutdown but your user table entry doesn't grant the
shutdown privilege to you, access is denied without even
checking the db or host tables. (They contain no
Shutdown_priv column, so there is no need to do so.)
For database-related requests (insert,
update, etc.), the server first checks the user's global
(superuser) privileges by looking in the user table entry. If the
entry allows the requested operation, access is granted. If the global
privileges in the user table are insufficient, the server
determines the user's database-specific privileges by checking the
db and host tables:
db table for a match on the
Host, Db, and User fields. The
Host and User fields are matched to the connecting
user's hostname and MySQL user name. The Db field is matched to
the database the user wants to access. If there is no entry for the
Host and User, access is denied.
db table entry and its
Host field is not blank, that entry defines the user's
database-specific privileges.
db table entry's Host field is
blank, it signifies that the host table enumerates which hosts
should be allowed access to the database. In this case, a further lookup is
done in the host table to find a match on the Host
and Db fields. If no host table entry matches,
access is denied. If there is a match, the user's database-specific privileges
are computed as the intersection (not the union!) of the privileges
in the db and host table entries, that is, the
privileges that are 'Y' in both entries. (This way you can grant
general privileges in the db table entry and then selectively
restrict them on a host-by-host basis using the host table
entries.) After determining the database-specific privileges granted by the
db and host table entries, the server adds them to the
global privileges granted by the user table. If the result allows
the requested operation, access is granted. Otherwise, the server checks the
user's table and column privileges in the tables_priv and
columns_priv tables and adds those to the user's privileges. Access
is allowed or denied based on the result.
Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarised like this:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
It may not be apparent why, if the global user entry privileges
are initially found to be insufficient for the requested operation, the server
adds those privileges to the database-, table-, and column-specific privileges
later. The reason is that a request might require more than one type of
privilege. For example, if you execute an INSERT ... SELECT
statement, you need both insert and select
privileges. Your privileges might be such that the user table entry
grants one privilege and the db table entry grants the other. In
this case, you have the necessary privileges to perform the request, but the
server cannot tell that from either table by itself; the privileges granted by
the entries in both tables must be combined.
The host table can be used to maintain a list of secure servers.
At TcX, the host table contains a list of all machines on the
local network. These are granted all privileges.
You can also use the host table to indicate hosts that are
not secure. Suppose you have a machine public.your.domain
that is located in a public area that you do not consider secure. You can allow
access to all hosts on your network except that machine by using
host table entries like this:
+--------------------+----+- | Host | Db | ... +--------------------+----+- | public.your.domain | % | ... (all privileges set to 'N') | %.your.domain | % | ... (all privileges set to 'Y') +--------------------+----+-
Naturally, you should always test your entries in the grant tables (for
example, using mysqlaccess) to make sure your access privileges are
actually set up the way you think they are.
Access denied ErrorsIf you encounter Access denied errors when you try to connect to
the MySQL server, the list below indicates some courses of action you can take
to correct the problem:
mysql_install_db
script to set up the initial grant table contents? If not, do so. See section
4.3.4
Setting Up the Initial MySQL Privileges. Test the initial privileges by
executing this command: shell> mysql -u root testThe server should let you connect without error. You should also make sure you have a file `user.MYD' in the MySQL database directory. Ordinarily, this is `PATH/var/mysql/user.MYD', where
PATH is the pathname to the MySQL installation root.
shell> mysql -u root mysqlThe server should let you connect because the MySQL
root
user has no password initially. That is also a security risk, so setting the
root password is something you should do while you're setting up
your other MySQL users. If you try to connect as root and get
this error: Access denied for user: '@unknown' to database mysqlthis means that you don't have an entry in the
user table
with a User column value of 'root' and that
mysqld cannot resolve the hostname for your client. In this case,
you must restart the server with the --skip-grant-tables option
and edit your `/etc/hosts' or `\windows\hosts' file to add
an entry for your host.
shell> mysqladmin -u root -pxxxx ver Access denied for user: 'root@localhost' (Using password: YES)It means that you are using a wrong password. See section 4.3.6 Setting Up Passwords. If you have forgot the root password, you can restart
mysqld with --skip-grant-tables to change
the password. You can find more about this option later on in this manual
section. If you get the above error even if you haven't specified a password,
this means that you a wrong password in some my.ini file. See
section 4.1.2
my.cnf Option Files. You can avoid using option files with the
--no-defaults option, as follows: shell> mysqladmin --no-defaults -u root ver
mysql_fix_privilege_tables script? If not, do so. The
structure of the grant tables changed with MySQL Version 3.22.11 when the
GRANT statement became functional.
PASSWORD() function if you set the password with the
INSERT, UPDATE, or SET PASSWORD
statements. The PASSWORD() function is unnecessary if you specify
the password using the GRANT ... INDENTIFIED BY statement or the
mysqladmin password command. See section 4.3.6
Setting Up Passwords.
localhost is a synonym for your local hostname, and is also
the default host to which clients try to connect if you specify no host
explicitly. However, connections to localhost do not work if you
are running on a system that uses MIT-pthreads (localhost
connections are made using Unix sockets, which are not supported by
MIT-pthreads). To avoid this problem on such systems, you should use the
--host option to name the server host explicitly. This will make
a TCP/IP connection to the mysqld server. In this case, you must
have your real hostname in user table entries on the server host.
(This is true even if you are running a client program on the same host as the
server.)
Access denied error when trying to connect to
the database with mysql -u user_name db_name, you may have a
problem with the user table. Check this by executing mysql
-u root mysql and issuing this SQL statement: mysql> SELECT * FROM user;The result should include an entry with the
Host and
User columns matching your computer's hostname and your MySQL
user name.
Access denied error message will tell you who you are
trying to log in as, the host from which you are trying to connect, and
whether or not you were using a password. Normally, you should have one entry
in the user table that exactly matches the hostname and user name
that were given in the error message. For example if you get an error message
that contains Using password: NO, this means that you tried to
login without an password.
user table that matches that host: Host ... is not allowed to connect to this MySQL serverYou can fix this by using the command-line tool
mysql (on
the server host!) to add a row to the user, db, or
host table for the user/hostname combination from which you are
trying to connect and then execute mysqladmin flush-privileges.
If you are not running MySQL Version 3.22 and you don't know the IP number or
hostname of the machine from which you are connecting, you should put an entry
with '%' as the Host column value in the
user table and restart mysqld with the
--log option on the server machine. After trying to connect from
the client machine, the information in the MySQL log will indicate how you
really did connect. (Then replace the '%' in the
user table entry with the actual hostname that shows up in the
log. Otherwise, you'll have a system that is insecure.) Another reason for
this error on Linux is that you are using a binary MySQL version that is
compiled with a different glibc version than the one you are using. In this
case you should either upgrade your OS/glibc or download the source MySQL
version and compile this yourself. A source RPM is normally trivial to compile
and install, so this isn't a big problem.
shell> mysqladmin -u root -pxxxx -h some-hostname ver Access denied for user: 'root@' (Using password: YES)This means that MySQL got some error when trying to resolve the IP to a hostname. In this case you can execute
mysqladmin flush-hosts to
reset the internal DNS cache. See section 5.5.5 How
MySQL uses DNS. Some permanent solutions are:
mysqld with --skip-name-resolve.
mysqld with --skip-host-cache.
localhost if you are running the server and the
client on the same machine.
/etc/hosts. mysql -u root test works but mysql -h your_hostname
-u root test results in Access denied, then you may not
have the correct name for your host in the user table. A common
problem here is that the Host value in the user table entry
specifies an unqualified hostname, but your system's name resolution routines
return a fully qualified domain name (or vice-versa). For example, if you have
an entry with host 'tcx' in the user table, but your
DNS tells MySQL that your hostname is 'tcx.subnet.se', the entry
will not work. Try adding an entry to the user table that
contains the IP number of your host as the Host column value.
(Alternatively, you could add an entry to the user table with a
Host value that contains a wild card--for example,
'tcx.%'. However, use of hostnames ending with `%'
is insecure and is not recommended!)
mysql -u user_name test works but mysql -u user_name
other_db_name doesn't work, you don't have an entry for
other_db_name listed in the db table.
mysql -u user_name db_name works when executed on the
server machine, but mysql -u host_name -u user_name db_name
doesn't work when executed on another client machine, you don't have the
client machine listed in the user table or the db
table.
Access denied, remove
from the user table all entries that have Host
values containing wild cards (entries that contain `%' or
`_'). A very common error is to insert a new entry with
Host='%' and User='some
user', thinking that this will allow you to specify
localhost to connect from the same machine. The reason that this
doesn't work is that the default privileges include an entry with
Host='localhost' and
User=''. Because that entry has a Host
value 'localhost' that is more specific than '%', it
is used in preference to the new entry when connecting from
localhost! The correct procedure is to insert a second entry with
Host='localhost' and
User='some_user', or to remove the entry with
Host='localhost' and
User=''.
db or host table: Access to database deniedIf the entry selected from the
db table has an empty value
in the Host column, make sure there are one or more corresponding
entries in the host table specifying which hosts the
db table entry applies to. If you get the error when using the
SQL commands SELECT ... INTO OUTFILE or LOAD DATA
INFILE, your entry in the user table probably doesn't have
the file privilege enabled.
Access denied when you run a
client without any options, make sure you haven't specified an old password in
any of your option files! See section 4.1.2
my.cnf Option Files.
INSERT or UPDATE statement) and your changes seem to
be ignored, remember that you must issue a FLUSH PRIVILEGES
statement or execute a mysqladmin flush-privileges command to
cause the server to re-read the privilege tables. Otherwise your changes have
no effect until the next time the server is restarted. Remember that after you
set the root password with an UPDATE command, you
won't need to specify it until after you flush the privileges, because the
server won't know you've changed the password yet!
mysql -u user_name db_name or
mysql -u user_name -pyour_pass db_name. If you are able to
connect using the mysql client, there is a problem with your
program and not with the access privileges. (Note that there is no space
between -p and the password; you can also use the
--password=your_pass syntax to specify the password. If you use
the -p option alone, MySQL will prompt you for the password.)
mysqld daemon with the
--skip-grant-tables option. Then you can change the MySQL grant
tables and use the mysqlaccess script to check whether or not
your modifications have the desired effect. When you are satisfied with your
changes, execute mysqladmin flush-privileges to tell the
mysqld server to start using the new grant tables.
Note: Reloading the grant tables overrides the
--skip-grant-tables option. This allows you to tell the server to
begin using the grant tables again without bringing it down and restarting it.
mysqld daemon with a
debugging option (for example, --debug=d,general,query). This
will print host and user information about attempted connections, as well as
information about each command issued. See section E.1.2
Creating trace files.
mysqldump mysql
command. As always, post your problem using the mysqlbug script.
See section 1.6.2.3
How to Report Bugs or Problems. In some cases you may need to restart
mysqld with --skip-grant-tables to run
mysqldump. GRANT and REVOKE SyntaxGRANT priv_type [(column_list)] [, priv_type [(column_list)] ...]
ON {tbl_name | * | *.* | db_name.*}
TO user_name [IDENTIFIED BY 'password']
[, user_name [IDENTIFIED BY 'password'] ...]
[REQUIRE
[{SSL| X509}]
[CIPHER cipher [AND]]
[ISSUER issuer [AND]]
[SUBJECT subject]]
[WITH GRANT OPTION]
REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...]
ON {tbl_name | * | *.* | db_name.*}
FROM user_name [, user_name ...]
GRANT is implemented in MySQL Version 3.22.11 or later. For
earlier MySQL versions, the GRANT statement does nothing.
The GRANT and REVOKE commands allow system
administrators to create users and grant and revoke rights to MySQL users at
four privilege levels:
mysql.user table.
mysql.db and mysql.host
tables.
mysql.tables_priv table.
mysql.columns_priv table. If you give a grant for a users that doesn't exists, that user is created.
For examples of how GRANT works, see section 4.3.5
Adding New Users to MySQL.
For the GRANT and REVOKE statements,
priv_type may be specified as any of the following:
ALL PRIVILEGES FILE RELOAD ALTER INDEX SELECT CREATE INSERT SHUTDOWN DELETE PROCESS UPDATE DROP REFERENCES USAGE
ALL is a synonym for ALL PRIVILEGES.
REFERENCES is not yet implemented. USAGE is currently
a synonym for ``no privileges.'' It can be used when you want to create a user
that has no privileges.
To revoke the grant privilege from a user, use a
priv_type value of GRANT OPTION:
REVOKE GRANT OPTION ON ... FROM ...;
The only priv_type values you can specify for a table are
SELECT, INSERT, UPDATE,
DELETE, CREATE, DROP, GRANT,
INDEX, and ALTER.
The only priv_type values you can specify for a column (that is,
when you use a column_list clause) are SELECT,
INSERT, and UPDATE.
You can set global privileges by using ON *.* syntax. You can
set database privileges by using ON db_name.* syntax. If you
specify ON * and you have a current database, you will set the
privileges for that database. (Warning: If you specify ON
* and you don't have a current database, you will affect the
global privileges!)
In order to accommodate granting rights to users from arbitrary hosts, MySQL
supports specifying the user_name value in the form
user@host. If you want to specify a user string
containing special characters (such as `-'), or a host
string containing special characters or wild-card characters (such as
`%'), you can quote the user or host name (for example,
'test-user'@'test-hostname').
You can specify wild cards in the hostname. For example,
user@"%.loc.gov" applies to user for any host in the
loc.gov domain, and user@"144.155.166.%" applies to
user for any host in the 144.155.166 class C subnet.
The simple form user is a synonym for user@"%".
MySQL doesn't support wildcards in user names. Anonymous users are defined by
inserting entries with User='' into the mysql.user
table or creating an user with an empty name with the GRANT
command.
Note: If you allow anonymous users to connect to the MySQL
server, you should also grant privileges to all local users as
user@localhost because otherwise the anonymous user entry for the
local host in the mysql.user table will be used when the user tries
to log into the MySQL server from the local machine!
You can verify if this applies to you by executing this query:
mysql> SELECT Host,User FROM mysql.user WHERE User='';
For the moment, GRANT only supports host, table, database, and
column names up to 60 characters long. A user name can be up to 16 characters.
The privileges for a table or column are formed from the logical OR of the
privileges at each of the four privilege levels. For example, if the
mysql.user table specifies that a user has a global
select privilege, this can't be denied by an entry at the
database, table, or column level.
The privileges for a column can be calculated as follows:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
In most cases, you grant rights to a user at only one of the privilege levels, so life isn't normally as complicated as above. The details of the privilege-checking procedure are presented in section 4.2 General Security Issues and the MySQL Access Privilege System.
If you grant privileges for a user/hostname combination that does not exist
in the mysql.user table, an entry is added and remains there until
deleted with a DELETE command. In other words, GRANT
may create user table entries, but REVOKE will not
remove them; you must do that explicitly using DELETE.
In MySQL Version 3.22.12 or later, if a new user is
created or if you have global grant privileges, the user's password will be set
to the password specified by the IDENTIFIED BY clause, if one is
given. If the user already had a password, it is replaced by the new one.
Warning: If you create a new user but do not specify an
IDENTIFIED BY clause, the user has no password. This is insecure.
Passwords can also be set with the SET PASSWORD command. See
section 5.5.6
SET Syntax.
If you grant privileges for a database, an entry in the mysql.db
table is created if needed. When all privileges for the database have been
removed with REVOKE, this entry is deleted.
If a user doesn't have any privileges on a table, the table is not displayed
when the user requests a list of tables (for example, with a SHOW
TABLES statement).
The WITH GRANT OPTION clause gives the user the ability to give
to other users any privileges the user has at the specified privilege level. You
should be careful to whom you give the grant privilege, as two
users with different privileges may be able to join privileges!
You cannot grant another user a privilege you don't have yourself; the grant privilege allows you to give away only those privileges you possess.
Be aware that when you grant a user the grant privilege at a
particular privilege level, any privileges the user already possesses (or is
given in the future!) at that level are also grantable by that user. Suppose you
grant a user the insert privilege on a database. If you then
grant the select privilege on the database and specify
WITH GRANT OPTION, the user can give away not only the
select privilege, but also insert. If you then
grant the update privilege to the user on the database, the
user can give away the insert, select and
update.
You should not grant alter privileges to a normal user. If you do that, the user can try to subvert the privilege system by renaming tables!
Note that if you are using table or column privileges for even one user, the server examines table and column privileges for all users and this will slow down MySQL a bit.
When mysqld starts, all privileges are read into memory.
Database, table, and column privileges take effect at once, and user-level
privileges take effect the next time the user connects. Modifications to the
grant tables that you perform using GRANT or REVOKE
are noticed by the server immediately. If you modify the grant tables manually
(using INSERT, UPDATE, etc.), you should execute a
FLUSH PRIVILEGES statement or run mysqladmin
flush-privileges to tell the server to reload the grant tables. See
section 4.3.3
When Privilege Changes Take Effect.
The biggest differences between the ANSI SQL and MySQL
versions of GRANT are:
TRIGGER, EXECUTE or UNDER
privileges.
INSERT grant on only part of the
columns in a table, you can execute INSERT statements on the
table; The columns for which you don't have the INSERT privilege
will set to their default values. ANSI SQL requires you to have the
INSERT privilege on all columns.
REVOKE commands or by manipulating the
MySQL grant tables. For a description of using REQUIRE, see See section 4.3.8
Using Secure Connections.
There are several distinctions between the way user names and passwords are used by MySQL and the way they are used by Unix or Windows:
-u or --user options.
This means that you can't make a database secure in any way unless all MySQL
user names have passwords. Anyone may attempt to connect to the server using
any name, and they will succeed if they specify any name that doesn't have a
password.
PASSWORD() and ENCRYPT() functions in section 6.3.5.2
Miscellaneous Functions. Note that even if the password is stored
'scrambled', and knowing your 'scrambled' password is enough to be able to
connect to the MySQL server! MySQL users and their privileges are normally created with the
GRANT command. See section 4.3.1
GRANT and REVOKE Syntax.
When you login to a MySQL server with a command line client you should
specify the password with --password=your-password. See section 4.2.7
Connecting to the MySQL Server.
mysql --user=monty --password=guess database_name
If you want the client to prompt for a password, you should use
--password without any argument
mysql --user=monty --password database_name
or the short form:
mysql -u monty -p database_name
Note that in the last example the password is not 'database_name'.
If you want to use the -p option to supply a password you should
do so like this:
mysql -u monty -pguess database_name
On some systems, the library call that MySQL uses to prompt for a password will automatically cut the password to 8 characters. Internally MySQL doesn't have any limit for the length of the password.
When mysqld starts, all grant table contents are read into
memory and become effective at that point.
Modifications to the grant tables that you perform using GRANT,
REVOKE, or SET PASSWORD are noticed by the server
immediately.
If you modify the grant tables manually (using INSERT,
UPDATE, etc.), you should execute a FLUSH PRIVILEGES
statement or run mysqladmin flush-privileges or mysqladmin
reload to tell the server to reload the grant tables. Otherwise your
changes will have no effect until you restart the server. If you change
the grant tables manually but forget to reload the privileges, you will be
wondering why your changes don't seem to make any difference!
When the server notices that the grant tables have been changed, existing client connections are affected as follows:
USE
db_name command. Global privilege changes and password changes take effect the next time the client connects.
After installing MySQL, you set up the initial access privileges by running
scripts/mysql_install_db. See section 2.3.1
Quick Installation Overview. The mysql_install_db script starts
up the mysqld server, then initialises the grant tables to contain
the following set of privileges:
root user is created as a superuser who can do
anything. Connections must be made from the local host. Note:
The initial root password is empty, so anyone can connect as
root without a password and be granted all privileges.
'test' or starting with
'test_'. Connections must be made from the local host. This means
any local user can connect without a password and be treated as the anonymous
user.
mysqladmin shutdown or mysqladmin processlist.
Note: The default privileges are different for Windows. See section 2.6.2.3 Running MySQL on Windows.
Because your installation is initially wide open, one of the first things you
should do is specify a password for the MySQL root user. You can do
this as follows (note that you specify the password using the
PASSWORD() function):
shell> mysql -u root mysql
mysql> SET PASSWORD FOR root@localhost=PASSWORD('new_password');
If you know what you are doing, you can also directly manipulate the privilege tables:
shell> mysql -u root mysql
mysql> UPDATE user SET Password=PASSWORD('new_password')
WHERE user='root';
mysql> FLUSH PRIVILEGES;
Another way to set the password is by using the mysqladmin
command:
shell> mysqladmin -u root password new_password
Only users with write/update access to the mysql database can
change the password for others users. All normal users (not anonymous ones) can
only change their own password with either of the above commands or with
SET PASSWORD=PASSWORD('new password').
Note that if you update the password in the user table directly
using the first method, you must tell the server to re-read the grant tables
(with FLUSH PRIVILEGES), because the change will go unnoticed
otherwise.
Once the root password has been set, thereafter you must supply
that password when you connect to the server as root.
You may wish to leave the root password blank so that you don't
need to specify it while you perform additional setup or testing. However, be
sure to set it before using your installation for any real production work.
See the scripts/mysql_install_db script to see how it sets up
the default privileges. You can use this as a basis to see how to add other
users.
If you want the initial privileges to be different than those just described
above, you can modify mysql_install_db before you run it.
To re-create the grant tables
completely, remove all the `.frm', `.MYI', and `.MYD'
files in the directory containing the mysql database. (This is the
directory named `mysql' under the database directory, which is listed
when you run mysqld --help.) Then run the
mysql_install_db script, possibly after editing it first to have
the privileges you want.
Note: For MySQL versions older than Version 3.22.10, you
should not delete the `.frm' files. If you accidentally do this, you
should copy them back from your MySQL distribution before running
mysql_install_db.
You can add users two different ways: by using GRANT statements
or by manipulating the MySQL grant tables directly. The preferred method is to
use GRANT statements, because they are more concise and less
error-prone. See section 4.3.1
GRANT and REVOKE Syntax.
There are also a lot of contributed programs like phpmyadmin
that can be used to create and administrate users. See section 1.6.1 MySQL
Portals.
The examples below show how to use the mysql client to set up
new users. These examples assume that privileges are set up according to the
defaults described in the previous section. This means that to make changes, you
must be on the same machine where mysqld is running, you must
connect as the MySQL root user, and the root user must
have the insert privilege for the mysql database
and the reload administrative privilege. Also, if you have
changed the root user password, you must specify it for the
mysql commands below.
You can add new users by issuing GRANT statements:
shell> mysql --user=root mysql
mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysql> GRANT ALL PRIVILEGES ON *.* TO monty@"%"
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost;
mysql> GRANT USAGE ON *.* TO dummy@localhost;
These GRANT statements set up three new users:
monty
'some_pass' to do so. Note that we must issue
GRANT statements for both monty@localhost and
monty@"%". If we don't add the entry with localhost,
the anonymous user entry for localhost that is created by
mysql_install_db will take precedence when we connect from the
local host, because it has a more specific Host field value and
thus comes earlier in the user table sort order.
admin
localhost without a password and
who is granted the reload and process
administrative privileges. This allows the user to execute the
mysqladmin reload, mysqladmin refresh, and
mysqladmin flush-* commands, as well as mysqladmin
processlist . No database-related privileges are granted. (They can be
granted later by issuing additional GRANT statements.)
dummy
'N' -- the
USAGE privilege type allows you to create a user with no
privileges. It is assumed that you will grant database-specific privileges
later. You can also add the same user access
information directly by issuing INSERT statements and then telling
the server to reload the grant tables:
shell> mysql --user=root mysql
mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO user VALUES('%','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO user SET Host='localhost',User='admin',
Reload_priv='Y', Process_priv='Y';
mysql> INSERT INTO user (Host,User,Password)
VALUES('localhost','dummy','');
mysql> FLUSH PRIVILEGES;
Depending on your MySQL version, you may have to use a different number of
'Y' values above (versions prior to Version 3.22.11 had fewer
privilege columns). For the admin user, the more readable extended
INSERT syntax that is available starting with Version 3.22.11 is
used.
Note that to set up a superuser, you need only create a user
table entry with the privilege fields set to 'Y'. No
db or host table entries are necessary.
The privilege columns in the user table were not set explicitly
in the last INSERT statement (for the dummy user), so
those columns are assigned the default value of 'N'. This is the
same thing that GRANT USAGE does.
The following example adds a user custom who can connect from
hosts localhost, server.domain, and
whitehouse.gov. He wants to access the bankaccount
database only from localhost, the expenses database
only from whitehouse.gov, and the customer database
from all three hosts. He wants to use the password stupid from all
three hosts.
To set up this user's privileges using GRANT statements, run
these commands:
shell> mysql --user=root mysql
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON bankaccount.*
TO custom@localhost
IDENTIFIED BY 'stupid';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON expenses.*
TO custom@whitehouse.gov
IDENTIFIED BY 'stupid';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON customer.*
TO custom@'%'
IDENTIFIED BY 'stupid';
The reason that we do to grant statements for the user 'custom' is that we want the give the user access to MySQL both from the local machine with Unix sockets and from the remote machine 'whitehouse.gov' over TCP/IP.
To set up the user's privileges by modifying the grant tables directly, run
these commands (note the FLUSH PRIVILEGES at the end):
shell> mysql --user=root mysql
mysql> INSERT INTO user (Host,User,Password)
VALUES('localhost','custom',PASSWORD('stupid'));
mysql> INSERT INTO user (Host,User,Password)
VALUES('server.domain','custom',PASSWORD('stupid'));
mysql> INSERT INTO user (Host,User,Password)
VALUES('whitehouse.gov','custom',PASSWORD('stupid'));
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y');
mysql> FLUSH PRIVILEGES;
The first three INSERT statements add user table
entries that allow user custom to connect from the various hosts
with the given password, but grant no permissions to him (all privileges are set
to the default value of 'N'). The next three INSERT
statements add db table entries that grant privileges to
custom for the bankaccount, expenses, and
customer databases, but only when accessed from the proper hosts.
As usual, when the grant tables are modified directly, the server must be told
to reload them (with FLUSH PRIVILEGES) so that the privilege
changes take effect.
If you want to give a specific user access from any machine in a given
domain, you can issue a GRANT statement like the following:
mysql> GRANT ...
ON *.*
TO myusername@"%.mydomainname.com"
IDENTIFIED BY 'mypassword';
To do the same thing by modifying the grant tables directly, do this:
mysql> INSERT INTO user VALUES ('%.mydomainname.com', 'myusername',
PASSWORD('mypassword'),...);
mysql> FLUSH PRIVILEGES;
You can also use xmysqladmin, mysql_webadmin, and
even xmysql to insert, change, and update values in the grant
tables. You can find these utilities in the Contrib directory of the MySQL web
site (http://mysql.com/Downloads/Contrib/).
In most cases you should use GRANT to set up your
users/passwords, so the following only applies for advanced users. See section
4.3.1
GRANT and REVOKE Syntax.
The examples in the preceding sections illustrate an important principle:
when you store a non-empty password using INSERT or
UPDATE statements, you must use the PASSWORD()
function to encrypt it. This is because the user table stores
passwords in encrypted form, not as plaintext. If you forget that fact, you are
likely to attempt to set passwords like this:
shell> mysql -u root mysql
mysql> INSERT INTO user (Host,User,Password)
VALUES('%','jeffrey','biscuit');
mysql> FLUSH PRIVILEGES;
The result is that the plaintext value 'biscuit' is stored as
the password in the user table. When the user jeffrey
attempts to connect to the server using this password, the mysql
client encrypts it with PASSWORD(), generates an authentification
vector based on encrypted password and a random number,
obtained from server, and sends the result to the server. The server uses the
password value in the user table (that is not
encrypted value 'biscuit') to perform the same
calculations, and compares results. The comparison fails and the server rejects
the connection:
shell> mysql -u jeffrey -pbiscuit test Access denied
Passwords must be encrypted when they are inserted in the user
table, so the INSERT statement should have been specified like this
instead:
mysql> INSERT INTO user (Host,User,Password)
VALUES('%','jeffrey',PASSWORD('biscuit'));
You must also use the PASSWORD() function when you use SET
PASSWORD statements:
mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');
If you set passwords using the GRANT ... IDENTIFIED BY statement
or the mysqladmin password command, the PASSWORD()
function is unnecessary. They both take care of encrypting the password for you,
so you would specify a password of 'biscuit' like this:
mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';
or
shell> mysqladmin -u jeffrey password biscuit
NOTE: PASSWORD() does not perform password
encryption in the same way that Unix passwords are encrypted. You should not
assume that if your Unix password and your MySQL password are the same, that
PASSWORD() will result in the same encrypted value as is stored in
the Unix password file. See section 4.3.2
MySQL User Names and Passwords.
It is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed below, along with an assessment of the risks of each method:
mysql.user table.
Knowing the encrypted password for a user makes it possible to login as this
user. The passwords are only scrambled so that one shouldn't be able to see
the real password you used (if you happen to use a similar password with your
other applications).
-pyour_pass or --password=your_pass option
on the command line. This is convenient but insecure, because your password
becomes visible to system status programs (such as ps) that may
be invoked by other users to display command lines. (MySQL clients typically
overwrite the command-line argument with zeroes during their initialisation
sequence, but there is still a brief interval during which the value is
visible.)
-p or --password option (with no
your_pass value specified). In this case, the client program
solicits the password from the terminal: shell> mysql -u user_name -p Enter password: ********The `*' characters represent your password. It is more secure to enter your password this way than to specify it on the command line because it is not visible to other users. However, this method of entering a password is suitable only for programs that you run interactively. If you want to invoke a client from a script that runs non-interactively, there is no opportunity to enter the password from the terminal. On some systems, you may even find that the first line of your script is read and interpreted (incorrectly) as your password!
[client] section of
the `.my.cnf' file in your home directory: [client] password=your_passIf you store your password in `.my.cnf', the file should not be group or world readable or writable. Make sure the file's access mode is
400 or 600. See section 4.1.2
my.cnf Option Files.
MYSQL_PWD environment
variable, but this method must be considered extremely insecure and should not
be used. Some versions of ps include an option to display the
environment of running processes; your password will be in plain sight for all
to see if you set MYSQL_PWD. Even on systems without such a
version of ps, it is unwise to assume there is no other method to
observe process environments. See section F
Environment Variables. All in all, the safest methods are to have the client program prompt for the password or to specify the password in a properly protected `.my.cnf' file.
MySQL has support for SSL encrypted connections. To understand how MySQL uses SSL, we need to explain some basics about SSL and X509. People who are already aware of it can skip this part.
By default, MySQL uses unencrypted connections between client and server. This means that someone could watch all your traffic and look at the data being sent/received. Actually, they could even change the data while it is in transit between client and server. Sometimes you need to move really secret data over public networks and in such a case using an unencrypted connection is unacceptable.
SSL is a protocol which uses different encryption algorithms to ensure that data which comes from public network can be trusted. It has mechanisms to detect any change, loss or replay of data. SSL also incorpores algorithms to recognise and provide identity verification using the X509 standard.
Encryption is the way to make any kind of data unreadable. In fact, today's practice requires many additional security elements from encryption algorithms. They should resist many kind of known attacks like just messing with order of encrypted messages or replaying data twice.
X509 is a standard that makes it possible to identify someone in the Internet. It is most commonly used in e-commerce applications. In basic terms, there should be some company called "Certificate Authority" which assigns electronic certificates to anyone who needs them. Certificates rely on asymmetric encryption algorithms which have two encryption keys - public and secret. A certificate owner can prove his identity by showing his certificate to other party. A certificate consists of his owner's public key. Any data encrypted with this public key can only be decrypted using the corresponding secret key, which is held by the owner of the certificate.
MySQL doesn't use encrypted on connections by default, because this would make the client/server protocol much slower. Any kind of additional functionality requires computer to do additional work and encrypting data is CPU-intensive operation require time and can delay MySQL main tasks. By default MySQL is tuned to be fast as possible.
If you need more information about SSL/X509/encryption, you should use your favourite internet search engine and search for keywords you are interested in.
To get secure connections to work with MySQL you must do the following:
--with-vio --with-openssl.
mysql.user table with some new columns. You can do this by
running the mysql_fix_privilege_tables.sh script.
openssl by
examining if SHOW VARIABLES LIKE 'have_openssl' returns
YES. MySQL can check X509 certificate attributes in addition to the normal username/password scheme. All the usual options are still required (username, password, IP address mask, database/table name).
There are different possibilities to limit connections:
REQUIRE SSL option limits the server to allow only SSL
encrypted connections. Note that this option can be omitted if there are any
ACL records which allow non-SSL connections. GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE SSL
REQUIRE X509 means that client should have valid certificate
but we do not care about the exact certificate, issuer or subject. The only
restriction is that it should be possible to verify its signature with one of
the CA certificates. GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE X509
REQUIRE ISSUER issuer makes connection more restrictive: now
client must present a valid X509 certificate issued by CA "issuer". Using X509
certificates always implies encryption, so the option "SSL" is not neccessary
anymore. GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE ISSUER "C=FI, ST=Some-State, L=Helsinki, O=MySQL Finland AB, CN=Tonu Samuel/Email=tonu@mysql.com"
REQUIRE SUBJECT subject requires clients to have valid X509
certificate with subject "subject" on it. If client have valid certificate but
having different "subject" then the connection is still not allowed. GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE SUBJECT "C=EE, ST=Some-State, L=Tallinn, O=MySQL demo client certificate, CN=Tonu Samuel/Email=tonu@mysql.com"
REQUIRE CIPHER cipher is needed to assure enough strong
ciphers and keylengths will be used. SSL itself can be weak if old algorithms
with short encryption keys are used. Using this option, we can ask for some
exact cipher method to allow a connection. GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE CIPHER "EDH-RSA-DES-CBC3-SHA"Also it is allowed to combine these options with each other like this:
GRANT ALL PRIVILEGES ON test.* TO root@localhost IDENTIFIED BY "goodsecret" REQUIRE SUBJECT "C=EE, ST=Some-State, L=Tallinn, O=MySQL demo client certificate, CN=Tonu Samuel/Email=tonu@mysql.com" AND ISSUER "C=FI, ST=Some-State, L=Helsinki, O=MySQL Finland AB, CN=Tonu Samuel/Email=tonu@mysql.com" AND CIPHER "EDH-RSA-DES-CBC3-SHA"But it is not allowed to use any of options twice. Only different options can be mixed.
Because MySQL tables are stored as files, it is easy to do a backup. To get a
consistent backup, do a LOCK TABLES on the relevant tables followed
by FLUSH TABLES for the tables. See section 6.7.2
LOCK TABLES/UNLOCK TABLES Syntax. See section 4.5.3
FLUSH Syntax. You only need a read lock; this allows other
threads to continue to query the tables while you are making a copy of the files
in the database directory. The FLUSH TABLE is needed to ensure that
the all active index pages is written to disk before you start the backup.
If you want to make a SQL level backup of a table, you can use SELECT
INTO OUTFILE or BACKUP TABLE. See section 6.4.1
SELECT Syntax. See section 4.4.2
BACKUP TABLE Syntax.
Another way to back up a database is to use the mysqldump
program or the mysqlhotcopy script. See section 4.8.5
mysqldump, Dumping Table Structure and Data. See section 4.8.6
mysqlhotcopy, Copying MySQL Databases and Tables.
shell> mysqldump --tab=/path/to/some/dir --opt --full or shell> mysqlhotcopy database /path/to/some/dirYou can also simply copy all table files (`*.frm', `*.MYD', and `*.MYI' files) as long as the server isn't updating anything. The script
mysqlhotcopy does use this method.
mysqld if it's running, then start it
with the --log-update[=file_name] option. See section 4.9.3
The Update Log. The update log file(s) provide you with the information
you need to replicate changes to the database that are made subsequent to the
point at which you executed mysqldump. If you have to restore something, try to recover your tables using
REPAIR TABLE or myisamchk -r first. That should work
in 99.9% of all cases. If myisamchk fails, try the following
procedure (this will only work if you have started MySQL with
--log-update, see section 4.9.3
The Update Log):
mysqldump backup.
shell> mysqlbinlog hostname-bin.[0-9]* | mysqlIf you are using the update log you can use:
shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql
ls is used to get all the update log files in the right order.
You can also do selective backups with SELECT * INTO OUTFILE
'file_name' FROM tbl_name and restore with LOAD DATA INFILE
'file_name' REPLACE ... To avoid duplicate records, you need a
PRIMARY KEY or a UNIQUE key in the table. The
REPLACE keyword causes old records to be replaced with new ones
when a new record duplicates an old record on a unique key value.
If you get performance problems in making backups on your system, you can solve this by setting up replication and do the backups on the slave instead of on the master. See section 4.10.1 Introduction.
If you are using a Veritas file system, you can do:
FLUSH TABLES WITH READ LOCK
mount vxfs
snapshot.
UNLOCK TABLES
BACKUP TABLE SyntaxBACKUP TABLE tbl_name[,tbl_name...] TO '/path/to/backup/directory'
Make a copy of all the table files to the backup directory that are the
minimum needed to restore it. Currenlty only works for MyISAM
tables. For MyISAM table, copies .frm (definition) and
.MYD (data) files. The index file can be rebuilt from those two.
Before using this command, please see See section 4.4.1 Database Backups.
During the backup, read lock will be held for each table, one at time, as
they are being backed up. If you want to backup several tables as a snapshot,
you must first issue LOCK TABLES obtaining a read lock for each
table in the group.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``backup'' |
| Msg_type | One of status, error, info or
warning. |
| Msg_text | The message. |
Note that BACKUP TABLE is only available in MySQL version
3.23.25 and later.
RESTORE TABLE SyntaxRESTORE TABLE tbl_name[,tbl_name...] FROM '/path/to/backup/directory'
Restores the table(s) from the backup that was made with BACKUP
TABLE. Existing tables will not be overwritten - if you try to restore
over an existing table, you will get an error. Restore will take longer than
BACKUP due to the need to rebuilt the index. The more keys you have, the longer
it is going to take. Just as BACKUP TABLE, currently only works of
MyISAM tables.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``restore'' |
| Msg_type | One of status, error, info or
warning. |
| Msg_text | The message. |
CHECK TABLE SyntaxCHECK TABLE tbl_name[,tbl_name...] [option [option...]] option = QUICK | FAST | MEDIUM | EXTENDED | CHANGED
CHECK TABLE only works on MyISAM tables. On
MyISAM tables it's the same thing as running myisamchk -m
table_name on the table.
If you don't specify any option MEDIUM is used.
Checks the table(s) for errors. For MyISAM tables the key
statistics is updated. The command returns a table with the following columns:
| Column | Value |
| Table | Table name. |
| Op | Always ``check''. |
| Msg_type | One of status, error, info, or
warning. |
| Msg_text | The message. |
Note that you can get many rows of information for each checked table. The
last row will be of Msg_type status and should normally be
OK. If you don't get OK, or Not checked
you should normally run a repair of the table. See section 4.4.6
Using myisamchk for Table Maintenance and Crash Recovery.
Not checked means that the table the given TYPE told
MySQL that there wasn't any need to check the table.
The different check types stand for the following:
| Type | Meaning |
QUICK |
Don't scan the rows to check for wrong links. |
FAST |
Only check tables which haven't been closed properly. |
CHANGED |
Only check tables which have been changed since last check or haven't been closed properly. |
MEDIUM |
Scan rows to verify that deleted links are okay. This also calculates a key checksum for the rows and verifies this with a calcualted checksum for the keys. |
EXTENDED |
Do a full key lookup for all keys for each row. This ensures that the table is 100 % consistent, but will take a long time! |
For dynamic sized MyISAM tables a started check will always do a
MEDIUM check. For static size rows we skip the row scan for
QUICK and FAST as the rows are very seldom corrupted.
You can combine check options as in:
CHECK TABLE test_table FAST QUICK;
Which only would do a quick check on the table if it wasn't closed properly.
Note: that in some case CHECK TABLE will change
the table! This happens if the table is marked as 'corrupted' or 'not closed
properly' but CHECK TABLE didn't find any problems in the table. In
this case CHECK TABLE will mark the table as okay.
If a table is corrupted, then it's most likely that the problem is in the indexes and not in the data part. All of the above check types checks the indexes throughly and should thus find most errors.
If you just want to check a table that you assume is okay, you should use no
check options or the QUICK option. The latter should be used when
you are in a hurry and can take the very small risk that QUICK
didn't find an error in the data file. (In most cases MySQL should find, under
normal usage, any error in the data file. If this happens then the table will be
marked as 'corrupted', in which case the table can't be used until it's
repaired.)
FAST and CHANGED are mostly intended to be used
from a script (for example to be executed from cron) if you want to check your
table from time to time. In most cases you FAST is to be prefered
over CHANGED. (The only case when it isn't is when you suspect a
bug you have found a bug in the MyISAM code.)
EXTENDED is only to be used after you have run a normal check
but still get strange errors from a table when MySQL tries to update a row or
find a row by key (this is very unlikely if a normal check has succeeded!).
Some things reported by check table, can't be corrected automatically:
Found row where the auto_increment column has the value 0.
This means that you have in the table a row where the
auto_increment index column contains the value 0. (It's possible
to create a row where the auto_increment column is 0 by explicitely setting
the column to 0 with an UPDATE statement) This isn't an error in
itself, but could cause trouble if you decide to dump the table and restore it
or do an ALTER TABLE on the table. In this case the
auto_increment column will change value, according to the rules of
auto_increment columns, which could cause problems like a duplicate key error.
To get rid of the warning, just execute an UPDATE statement to
set the column to some other value than 0. REPAIR TABLE SyntaxREPAIR TABLE tbl_name[,tbl_name...] [QUICK] [EXTENDED]
REPAIR TABLE only works on MyISAM tables and is the
same as running myisamchk -r table_name on the table.
Normally you should never have to run this command, but if disaster strikes
you are very likely to get back all your data from a MyISAM table with
REPAIR TABLE. If your tables get corrupted a lot you should try to
find the reason for this! See section A.4.1 What
To Do If MySQL Keeps Crashing. See section 7.1.3
MyISAM table problems..
REPAIR TABLE repairs a possible corrupted table. The command
returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``repair'' |
| Msg_type | One of status, error, info or
warning. |
| Msg_text | The message. |
Note that you can get many rows of information for each repaired table. The
last one row will be of Msg_type status and should normally be
OK. If you don't get OK, you should try repairing the
table with myisamchk -o, as REPAIR TABLE does not yet
implement all the options of myisamchk. In the near future, we will
make it more flexible.
If QUICK is given then MySQL will try to do a
REPAIR of only the index tree.
If you use EXTENDED then MySQL will create the index row by row
instead of creating one index at a time with sorting; This may be better than
sorting on fixed-length keys if you have long char() keys that
compress very good.
myisamchk for Table Maintenance
and Crash RecoveryStarting with MySQL Version 3.23.13, you can check MyISAM tables with the
CHECK TABLE command. See section 4.4.4
CHECK TABLE Syntax. You can repair tables with the REPAIR
TABLE command. See section 4.4.5
REPAIR TABLE Syntax.
To check/repair MyISAM tables (.MYI and .MYD) you
should use the myisamchk utility. To check/repair ISAM tables
(.ISM and .ISD) you should use the
isamchk utility. See section 7 MySQL
Table Types.
In the following text we will talk about myisamchk, but
everything also applies to the old isamchk.
You can use the myisamchk utility to get information about your
database tables, check and repair them, or optimise them. The following sections
describe how to invoke myisamchk (including a description of its
options), how to set up a table maintenance schedule, and how to use
myisamchk to perform its various functions.
You can, in most cases, also use the command OPTIMIZE TABLES to
optimise and repair tables, but this is not as fast or reliable (in case of real
fatal errors) as myisamchk. On the other hand, OPTIMIZE
TABLE is easier to use and you don't have to worry about flushing tables.
See section 4.5.1
OPTIMIZE TABLE Syntax.
Even that the repair in myisamchk is quite secure, it's always a
good idea to make a backup BEFORE doing a repair (or anything that could make a
lot of changes to a table)
myisamchk Invocation Syntaxmyisamchk is invoked like this:
shell> myisamchk [options] tbl_name
The options specify what you want myisamchk to do.
They are described below. (You can also get a list of options by invoking
myisamchk --help.) With no options, myisamchk simply
checks your table. To get more information or to tell myisamchk to
take corrective action, specify options as described below and in the following
sections.
tbl_name is the database table you want to check/repair. If you
run myisamchk somewhere other than in the database directory, you
must specify the path to the file, because myisamchk has no idea
where your database is located. Actually, myisamchk doesn't care
whether or not the files you are working on are located in a database directory;
you can copy the files that correspond to a database table into another location
and perform recovery operations on them there.
You can name several tables on the myisamchk command line if you
wish. You can also specify a name as an index file name (with the
`.MYI' suffix), which allows you to specify all tables in a directory
by using the pattern `*.MYI'. For example, if you are in a database
directory, you can check all the tables in the directory like this:
shell> myisamchk *.MYI
If you are not in the database directory, you can check all the tables there by specifying the path to the directory:
shell> myisamchk /path/to/database_dir/*.MYI
You can even check all tables in all databases by specifying a wild card with the path to the MySQL data directory:
shell> myisamchk /path/to/datadir/*/*.MYI
The recommended way to quickly check all tables is:
myisamchk --silent --fast /path/to/datadir/*/*.MYI isamchk --silent /path/to/datadir/*/*.ISM
If you want to check all tables and repair all tables that are corrupted, you can use the following line:
myisamchk --silent --force --fast --update-state -O key_buffer=64M -O sort_buffer=64M -O read_buffer=1M -O write_buffer=1M /path/to/datadir/*/*.MYI isamchk --silent --force -O key_buffer=64M -O sort_buffer=64M -O read_buffer=1M -O write_buffer=1M /path/to/datadir/*/*.ISM
The above assumes that you have more than 64 M free.
Note that if you get an error like:
myisamchk: warning: 1 clients is using or hasn't closed the table properly
This means that you are trying to check a table that has been updated by the
another program (like the mysqld server) that hasn't yet closed the
file or that has died without closing the file properly.
If you mysqld is running, you must force a sync/close of all
tables with FLUSH TABLES and ensure that no one is using the tables
while you are running myisamchk. In MySQL Version 3.23 the easiest
way to avoid this problem is to use CHECK TABLE instead of
myisamchk to check tables.
myisamchkmyisamchk supports the following options.
-# or --debug=debug_options
debug_options string often is
'd:t:o,filename'.
-? or --help
-O var=option, --set-variable var=option
myisamchk --help:
| Variable | Value |
| key_buffer_size | 523264 |
| read_buffer_size | 262136 |
| write_buffer_size | 262136 |
| sort_buffer_size | 2097144 |
| sort_key_blocks | 16 |
| decode_bits | 9 |
sort_buffer_size is used when the
keys are repaired by sorting keys, which is the normal case when you use
--recover. key_buffer_size is used when you are
checking the table with --extended-check or when the keys are
repaired by inserting key row by row in to the table (like when doing normal
inserts). Repairing through the key buffer is used in the following cases:
--safe-recover.
CHAR, VARCHAR or TEXT
keys as the sort needs to store the whole keys during sorting. If you have
lots of temporary space and you can force myisamchk to repair
by sorting you can use the --sort-recover option.
-s or --silent
-s twice (-ss) to make myisamchk very
silent.
-v or --verbose
-d and -e. Use -v multiple times
(-vv, -vvv) for more verbosity!
-V or --version
myisamchk version and exit.
-w or, --wait
mysqld
on the table with --skip-locking, the table can only be locked by
another myisamchk command. myisamchk-c or --check
myisamchk any options that override this.
-e or --extend-check
myisamchk or myisamchk --medium-check should, in
most cases, be able to find out if there are any errors in the table. If you
are using --extended-check and have much memory, you should
increase the value of key_buffer_size a lot!
-F or --fast
-C or --check-only-changed
-f or --force
myisamchk with -r (repair) on the table,
if myisamchk finds any errors in the table.
-i or --information
-m or --medium-check
-U or --update-state
--check-only-changed option, but you shouldn't use this option if
the mysqld server is using the table and you are running
mysqld with --skip-locking.
-T or --read-only
myisamchk to check a table that is in use by some other
application that doesn't use locking (like mysqld
--skip-locking). The following options are used if you start myisamchk with
-r or -o:
-D # or --data-file-length=#
-e or --extend-check
-f or --force
table_name.TMD) instead of
aborting.
-k # or keys-used=#
# indexes. If you are using MyISAM, tells
which keys to use, where each binary bit stands for one key (first key is bit
0). This can be used to get faster inserts! Deactivated indexes can be
reactivated by using myisamchk -r. keys.
-l or --no-symlinks
myisamchk repairs the
table a symlink points at. This option doesn't exist in MySQL 4.0, as MySQL
4.0 will not remove symlinks during repair.
-r or --recover
-r, you should then try
-o. (Note that in the unlikely case that -r fails,
the data file is still intact.) If you have lots of memory, you should
increase the size of sort_buffer_size!
-o or --safe-recover
-r, but can handle a couple of very unlikely cases that
-r cannot handle. This recovery method also uses much less disk
space than -r. Normally one should always first repair with
-r, and only if this fails use -o. If you have lots
of memory, you should increase the size of key_buffer_size!
-n or --sort-recover
myisamchk to use sorting to resolve the keys even if
the temporary files should be very big. This will not have any effect if you
have fulltext keys in the table.
--character-sets-dir=...
--set-character-set=name
.t or --tmpdir=path
myisamchk will use the environment variable TMPDIR
for this.
-q or --quick
-q to force myisamchk to modify the original
datafile in case of duplicate keys
-u or --unpack
myisamchkOther actions that myisamchk can do, besides repair and check
tables:
-a or --analyze
myisamchk --describe --verbose
table_name' or using SHOW KEYS in MySQL.
-d or --description
-A or --set-auto-increment[=value]
-S or --sort-index
-R or --sort-records=#
SELECT and ORDER
BY operations on this index. (It may be very slow to do a sort the
first time!) To find out a table's index numbers, use SHOW INDEX,
which shows a table's indexes in the same order that myisamchk
sees them. Indexes are numbered beginning with 1. myisamchk Memory UsageMemory allocation is important when you run myisamchk.
myisamchk uses no more memory than you specify with the
-O options. If you are going to use myisamchk on very
large files, you should first decide how much memory you want it to use. The
default is to use only about 3M to fix things. By using larger values, you can
get myisamchk to operate faster. For example, if you have more than
32M RAM, you could use options such as these (in addition to any other options
you might specify):
shell> myisamchk -O sort=16M -O key=16M -O read=1M -O write=1M ...
Using -O sort=16M should probably be enough for most cases.
Be aware that myisamchk uses temporary files in
TMPDIR. If TMPDIR points to a memory file system, you
may easily get out of memory errors. If this happens, set TMPDIR to
point at some directory with more space and restart myisamchk.
When repairing, myisamchk will also need a lot of disk space:
--quick, as in this
case only the index file will be re-created. This space is needed on the same
disk as the original record file!
--recover or --sort-recover (but not
when using --safe-recover), you will need space for a sort buffer
for: (largest_key + row_pointer_length)*number_of_rows * 2. You
can check the length of the keys and the row_pointer_length with
myisamchk -dv table. This space is allocated on the temporary
disk (specified by TMPDIR or --tmpdir=#). If you have a problem with disk space during repair, you can try to use
--safe-recover instead of --recover.
myisamchk for Crash
RecoveryIf you run mysqld with --skip-locking (which is the
default on some systems, like Linux), you can't reliably use
myisamchk to check a table when mysqld is using the
same table. If you can be sure that no one is accessing the tables through
mysqld while you run myisamchk, you only have to do
mysqladmin flush-tables before you start checking the tables. If
you can't guarantee the above, then you must take down mysqld while
you check the tables. If you run myisamchk while
mysqld is updating the tables, you may get a warning that a table
is corrupt even if it isn't.
If you are not using --skip-locking, you can use
myisamchk to check tables at any time. While you do this, all
clients that try to update the table will wait until myisamchk is
ready before continuing.
If you use myisamchk to repair or optimise tables, you
must always ensure that the mysqld server is not
using the table (this also applies if you are using
--skip-locking). If you don't take down mysqld you
should at least do a mysqladmin flush-tables before you run
myisamchk. Your tables may be corrupted if the
server and myisamchk access the tables simultaneously.
This chapter describes how to check for and deal with data corruption in MySQL databases. If your tables get corrupted frequently you should try to find the reason for this! See section A.4.1 What To Do If MySQL Keeps Crashing.
The MyISAM table section contains reason for why a table could
be corrupted. See section 7.1.3
MyISAM table problems..
When performing crash recovery, it is important to understand that each table
tbl_name in a database corresponds to three files in the database
directory:
| File | Purpose |
| `tbl_name.frm' | Table definition (form) file |
| `tbl_name.MYD' | Data file |
| `tbl_name.MYI' | Index file |
Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files.
myisamchk works by creating a copy of the `.MYD' (data)
file row by row. It ends the repair stage by removing the old `.MYD'
file and renaming the new file to the original file name. If you use
--quick, myisamchk does not create a temporary
`.MYD' file, but instead assumes that the `.MYD' file is
correct and only generates a new index file without touching the `.MYD'
file. This is safe, because myisamchk automatically detects if the
`.MYD' file is corrupt and aborts the repair in this case. You can also
give two --quick options to myisamchk. In this case,
myisamchk does not abort on some errors (like duplicate key) but
instead tries to resolve them by modifying the `.MYD' file. Normally
the use of two --quick options is useful only if you have too
little free disk space to perform a normal repair. In this case you should at
least make a backup before running myisamchk.
To check a MyISAM table, use the following commands:
myisamchk tbl_name
myisamchk without
options or with either the -s or --silent option.
myisamchk -m tbl_name
myisamchk -e tbl_name
-e means
``extended check''). It does a check-read of every key for each row to verify
that they indeed point to the correct row. This may take a long time on a big
table with many keys. myisamchk will normally stop after the
first error it finds. If you want to obtain more information, you can add the
--verbose (-v) option. This causes
myisamchk to keep going, up through a maximum of 20 errors. In
normal usage, a simple myisamchk (with no arguments other than
the table name) is sufficient.
myisamchk -e -i tbl_name
-i option tells
myisamchk to print some informational statistics, too. In the following section we only talk about using myisamchk on
MyISAM tables (extensions .MYI and .MYD).
If you are using ISAM tables (extensions .ISM and
.ISD), you should use isamchk instead.
Starting with MySQL Version 3.23.14, you can repair MyISAM tables with the
REPAIR TABLE command. See section 4.4.5
REPAIR TABLE Syntax.
The symptoms of a corrupted table include queries that abort unexpectedly and observable errors such as these:
perror ###. Here is the most common errors that
indicates a problem with the table: shell> perror 126 127 132 134 135 136 141 144 145 126 = Index file is crashed / Wrong file format 127 = Record-file is crashed 132 = Old database file 134 = Record was already deleted (or record file crashed) 135 = No more room in record file 136 = No more room in index file 141 = Duplicate unique key or constraint on write or update 144 = Table is crashed and last repair failed 145 = Table was marked as crashed and should be repairedNote that error 135, no more room in record file, is not an error that can be fixed by a simple repair. In this case you have to do:
ALTER TABLE table MAX_ROWS=xxx AVG_ROW_LENGTH=yyy;
In the other cases, you must repair your tables. myisamchk can
usually detect and fix most things that go wrong.
The repair process involves up to four stages, described below. Before you
begin, you should cd to the database directory and check the
permissions of the table files. Make sure they are readable by the Unix user
that mysqld runs as (and to you, because you need to access the
files you are checking). If it turns out you need to modify files, they must
also be writable by you.
If you are using MySQL Version 3.23.16 and above, you can (and should) use
the CHECK and REPAIR commands to check and repair
MyISAM tables. See section 4.4.4
CHECK TABLE Syntax. See section 4.4.5
REPAIR TABLE Syntax.
The manual section about table maintenance includes the options to
isamchk/myisamchk. See section 4.4.6
Using myisamchk for Table Maintenance and Crash Recovery.
The following section is for the cases where the above command fails or if
you want to use the extended features that
isamchk/myisamchk provides.
If you are going to repair a table from the command line, you must first take
down the mysqld server. Note that when you do mysqladmin
shutdown on a remote server, the mysqld server will still be
alive for a while after mysqladmin returns, until all queries are
stopped and all keys have been flushed to disk.
Stage 1: Checking your tables
Run myisamchk *.MYI or myisamchk -e *.MYI if you
have more time. Use the -s (silent) option to suppress unnecessary
information.
If the mysqld server is done you should use the --update option
to tell myisamchk to mark the table as 'checked'.
You have to repair only those tables for which myisamchk
announces an error. For such tables, proceed to Stage 2.
If you get weird errors when checking (such as out of memory
errors), or if myisamchk crashes, go to Stage 3.
Stage 2: Easy safe repair
Note: If you want repairing to go much faster, you should add: -O
sort_buffer=# -O key_buffer=# (where # is about 1/4 of the available
memory) to all isamchk/myisamchk commands.
First, try myisamchk -r -q tbl_name (-r -q means
``quick recovery mode''). This will attempt to repair the index file without
touching the data file. If the data file contains everything that it should and
the delete links point at the correct locations within the data file, this
should work, and the table is fixed. Start repairing the next table. Otherwise,
use the following procedure:
myisamchk -r tbl_name (-r means ``recovery
mode''). This will remove incorrect records and deleted records from the data
file and reconstruct the index file.
myisamchk --safe-recover
tbl_name. Safe recovery mode uses an old recovery method that handles a
few cases that regular recovery mode doesn't (but is slower). If you get weird errors when repairing (such as out of memory
errors), or if myisamchk crashes, go to Stage 3.
Stage 3: Difficult repair
You should only reach this stage if the first 16K block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it's necessary to create a new index file. Do so as follows:
shell> mysql db_name mysql> SET AUTOCOMMIT=1; mysql> TRUNCATE TABLE table_name; mysql> quitIf your SQL version doesn't have
TRUNCATE TABLE, use
DELETE FROM table_name instead.
Go back to Stage 2. myisamchk -r -q should work now. (This
shouldn't be an endless loop.)
Stage 4: Very difficult repair
You should reach this stage only if the description file has also crashed. That should never happen, because the description file isn't changed after the table is created:
myisamchk -r.
To coalesce fragmented records and eliminate wasted space resulting from
deleting or updating records, run myisamchk in recovery mode:
shell> myisamchk -r tbl_name
You can optimise a table in the same way using the SQL OPTIMIZE
TABLE statement. OPTIMIZE TABLE does a repair of the table,
a key analyses and also sorts the index tree to give faster key lookups. There
is also no possibility of unwanted interaction between a utility and the server,
because the server does all the work when you use OPTIMIZE TABLE.
See section 4.5.1
OPTIMIZE TABLE Syntax.
myisamchk also has a number of other options you can use to
improve the performance of a table:
For a full description of the option. See section 4.4.6.1
myisamchk Invocation Syntax.
Starting with MySQL Version 3.23.13, you can check MyISAM tables with the
CHECK TABLE command. See section 4.4.4
CHECK TABLE Syntax. You can repair tables with the REPAIR
TABLE command. See section 4.4.5
REPAIR TABLE Syntax.
It is a good idea to perform table checks on a regular basis rather than
waiting for problems to occur. For maintenance purposes, you can use
myisamchk -s to check tables. The -s option (short for
--silent) causes myisamchk to run in silent mode,
printing messages only when errors occur.
It's also a good idea to check tables when the server
starts up. For example, whenever the machine has done a reboot in the middle of
an update, you usually need to check all the tables that could have been
affected. (This is an ``expected crashed table''.) You could add a test to
safe_mysqld that runs myisamchk to check all tables
that have been modified during the last 24 hours if there is an old
`.pid' (process ID) file left after a reboot. (The `.pid' file
is created by mysqld when it starts up and removed when it
terminates normally. The presence of a `.pid' file at system startup
time indicates that mysqld terminated abnormally.)
An even better test would be to check any table whose last-modified time is more recent than that of the `.pid' file.
You should also check your tables regularly during normal system operation.
At MySQL AB, we run a cron job to check all our important tables
once a week, using a line like this in a `crontab' file:
35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI
This prints out information about crashed tables so we can examine and repair them when needed.
As we haven't had any unexpectedly crashed tables (tables that become corrupted for reasons other than hardware trouble) for a couple of years now (this is really true), once a week is more than enough for us.
We recommend that to start with, you execute myisamchk -s each
night on all tables that have been updated during the last 24 hours, until you
come to trust MySQL as much as we do.
Normally you don't need to maintain MySQL tables that
much. If you are changing tables with dynamic size rows (tables with
VARCHAR, BLOB or TEXT columns) or have
tables with many deleted rows you may want to from time to time (once a month?)
defragment/reclaim space from the tables.
You can do this by using OPTIMIZE TABLE on the tables in
question or if you can take the mysqld server down for a while do:
isamchk -r --silent --sort-index -O sort_buffer_size=16M */*.ISM myisamchk -r --silent --sort-index -O sort_buffer_size=16M */*.MYI
To get a description of a table or statistics about it, use the commands shown below. We explain some of the information in more detail later:
myisamchk in ``describe mode'' to
produce a description of your table. If you start the MySQL server using the
--skip-locking option, myisamchk may report an error
for a table that is updated while it runs. However, because
myisamchk doesn't change the table in describe mode, there isn't
any risk of destroying data.
myisamchk is doing, add -v to tell it to run in
verbose mode.
-eis, but tells you what
is being done. Example of myisamchk -d
output:
MyISAM file: company.MYI
Record format: Fixed length
Data records: 1403698 Deleted blocks: 0
Recordlength: 226
table description:
Key Start Len Index Type
1 2 8 unique double
2 15 10 multip. text packed stripped
3 219 8 multip. double
4 63 10 multip. text packed stripped
5 167 2 multip. unsigned short
6 177 4 multip. unsigned long
7 155 4 multip. text
8 138 4 multip. unsigned long
9 177 4 multip. unsigned long
193 1 text
Example of myisamchk -d -v output:
MyISAM file: company
Record format: Fixed length
File-version: 1
Creation time: 1999-10-30 12:12:51
Recover time: 1999-10-31 19:13:01
Status: checked
Data records: 1403698 Deleted blocks: 0
Datafile parts: 1403698 Deleted data: 0
Datafilepointer (bytes): 3 Keyfile pointer (bytes): 3
Max datafile length: 3791650815 Max keyfile length: 4294967294
Recordlength: 226
table description:
Key Start Len Index Type Rec/key Root Blocksize
1 2 8 unique double 1 15845376 1024
2 15 10 multip. text packed stripped 2 25062400 1024
3 219 8 multip. double 73 40907776 1024
4 63 10 multip. text packed stripped 5 48097280 1024
5 167 2 multip. unsigned short 4840 55200768 1024
6 177 4 multip. unsigned long 1346 65145856 1024
7 155 4 multip. text 4995 75090944 1024
8 138 4 multip. unsigned long 87 85036032 1024
9 177 4 multip. unsigned long 178 96481280 1024
193 1 text
Example of myisamchk -eis output:
Checking MyISAM file: company Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 98% Packed: 17% Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1626.51, System time 232.36 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 627, Swaps 0 Blocks in 0 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 639, Involuntary context switches 28966
Example of myisamchk -eiv output:
Checking MyISAM file: company Data records: 1403698 Deleted blocks: 0 - check file-size - check delete-chain block_size 1024: index 1: index 2: index 3: index 4: index 5: index 6: index 7: index 8: index 9: No recordlinks - check index reference - check data record references index: 1 Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 2 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 - check data record references index: 3 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 - check data record references index: 5 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 6 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 7 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 8 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 9 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 9% Packed: 17% - check records and index references [LOTS OF ROW NUMBERS DELETED] Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1639.63, System time 251.61 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0 Blocks in 4 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 10604, Involuntary context switches 122798
Here are the sizes of the data and index files for the table used in the preceding examples:
-rw-rw-r-- 1 monty tcx 317235748 Jan 12 17:30 company.MYD -rw-rw-r-- 1 davida tcx 96482304 Jan 12 18:35 company.MYM
Explanations for the types of information myisamchk produces are
given below. The ``keyfile'' is the index file. ``Record'' and ``row'' are
synonymous:
Data records.
.MYD
file) can become, in bytes.
.MYI file)
can become, in bytes.
Fixed length. Other possible values are
Compressed and Packed.
unique or multip. (multiple). Indicates
whether or not one value can exist multiple times in this index.
packed, stripped or
empty.
myisamchk -a. If this is not updated at all, a default
value of 30 is given. myisamchk, the values are very high (very near the theoretical
maximum).
CHAR/VARCHAR/DECIMAL keys. For
long strings like names, this can significantly reduce the space used. In the
third example above, the 4th key is 10 characters long and a 60% reduction in
space is achieved.
Packed value indicates the percentage of savings achieved by
doing this.
myisamchk. See section 4.4.6.10
Table Optimisation.
Linkdata is the sum of
the amount of storage used by all such pointers. If a table has been compressed with myisampack, myisamchk
-d prints additional information about each table column. See section 4.7.4
myisampack, The MySQL Compressed Read-only Table Generator, for an example
of this information and a description of what it means.
OPTIMIZE TABLE SyntaxOPTIMIZE TABLE tbl_name[,tbl_name]...
OPTIMIZE TABLE should be used if you have deleted a large part
of a table or if you have made many changes to a table with variable-length rows
(tables that have VARCHAR, BLOB, or TEXT
columns). Deleted records are maintained in a linked list and subsequent
INSERT operations reuse old record positions. You can use
OPTIMIZE TABLE to reclaim the unused space and to defragment the
data file.
For the moment OPTIMIZE TABLE only works on
MyISAM and BDB tables. For BDB
tables, OPTIMIZE TABLE is currently mapped to ANALYZE
TABLE. See section 4.5.2
ANALYZE TABLE Syntax.
You can get optimise table to work on other table types by starting
mysqld with --skip-new or --safe-mode,
but in this case OPTIMIZE TABLE is just mapped to ALTER
TABLE.
OPTIMIZE TABLE works the following way:
OPTIMIZE TABLE for MyISAM tables is equvialent of
running myisamchk --quick --check-changed-tables --sort-index
--analyze on the table.
Note that the table is locked during the time OPTIMIZE TABLE is
running!
ANALYZE TABLE SyntaxANALYZE TABLE tbl_name[,tbl_name...]
Analyse and store the key distribution for the table. During the analyse the
table is locked with a read lock. This works on MyISAM and
BDB tables.
This is equivalent to running myisamchk -a on the table.
MySQL uses the stored key distribution to decide in which order tables should be joined when one does a join on something else than a constant.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``analyze'' |
| Msg_type | One of status, error, info or
warning. |
| Msg_text | The message. |
You can check the stored key distribution with the SHOW INDEX
command. See section 4.5.6.1
Retrieving information about Database, Tables, Columns, and Indexes.
If the table hasn't changed since the last ANALYZE TABLE
command, the table will not be analysed again.
FLUSH SyntaxFLUSH flush_option [,flush_option]
You should use the FLUSH command if you want to clear some of
the internal caches MySQL uses. To execute FLUSH, you must have the
RELOAD privilege.
flush_option can be any of the following:
| Option | Description |
HOSTS |
Empties the host cache tables. You should flush the host tables if
some of your hosts change IP number or if you get the error message
Host ... is blocked. When more than
max_connect_errors errors occur in a row for a given host
while connection to the MySQL server, MySQL assumes something is wrong and
blocks the host from further connection requests. Flushing the host tables
allows the host to attempt to connect again. See section A.2.4
Host '...' is blocked Error. You can start
mysqld with -O max_connection_errors=999999999
to avoid this error message. |
DES_KEY_FILE |
Reloads the des keys from the file specified with
--des-key-file. |
LOGS |
Closes and reopens all log files. If you have specified the update log
file or a binary log file without an extension, the extension number of
the log file will be incremented by one relative to the previous file. If
you have used an extension in the file name, MySQL will close and reopen
the update log file. See section 4.9.3
The Update Log. This is the same thing as sending the
SIGHUP signal to the mysqld server. |
PRIVILEGES |
Reloads the privileges from the grant tables in the mysql
database. |
QUERY CACHE |
Defragment the query cache to better utilise its memory. This command will not remove any queries from the cache. |
TABLES |
Closes all open tables and force all tables in use to be closed. This also flushes the query cache. |
[TABLE | TABLES] table_name [,table_name...] |
Flushes only the given tables. |
TABLES WITH READ LOCK |
Closes all open tables and locks all tables for all databases with a
read until one executes UNLOCK TABLES. This is very
convenient way to get backups if you have a file system, like Veritas,that
can take snapshots in time. |
STATUS |
Resets most status variables to zero. This is something one should only use when debugging a query. |
You can also access each of the commands shown above with the
mysqladmin utility, using the flush-hosts,
flush-logs, reload, or flush-tables
commands.
Take also a look at the RESET command used with replication. See
section 4.5.4
RESET Syntax.
RESET SyntaxFLUSH flush_option [,flush_option]
The RESET command is used to clear things. It also acts as an
stronger version of the FLUSH command. See section 4.5.3
FLUSH Syntax.
| Option | Description |
MASTER @tab Deletes all binary logs listed in the index
file, resetting the binlog index file to be empty. In pre-3.23.26
versions, FLUSH MASTER (Master) | |
SLAVE @tab Makes the slave forget its replication
position in the master logs. In pre 3.23.26 versions the command was
called FLUSH SLAVE(Slave) | |
QUERY CACHE @tab Removes all query results from the query
cache. |
KILL SyntaxKILL thread_id
Each connection to mysqld runs in a separate thread. You can see
which threads are running with the SHOW PROCESSLIST command and
kill a thread with the KILL thread_id command.
If you have the process privilege, you can see and kill all threads. Otherwise, you can see and kill only your own threads.
You can also use the mysqladmin processlist and mysqladmin
kill commands to examine and kill threads.
When you do a KILL, a thread specific kill flag is
set for the thread.
In most cases it may take some time for the thread to die as the kill flag is only checked at specific intervals.
SELECT, ORDER BY and GROUP BY
loops, the flag is checked after reading a block of rows. If the kill flag is
set the statement is aborted
ALTER TABLE the kill flag is checked before
each block of rows are read from the original table. If the kill flag was set
the command is aborted and the temporary table is deleted.
UPDATE TABLE and DELETE TABLE, the
kill flag is checked after each block read and after each updated or delete
row. If the kill flag is set the statement is aborted. Note that if you are
not using transactions, the changes will not be rolled back!
GET_LOCK() will abort with NULL.
INSERT DELAYED thread will quickly flush all rows it has
in memory and die.
Locked),
the table lock will be quickly aborted.
write call,
the write is aborted with an disk full error message. SHOW SyntaxSHOW DATABASES [LIKE wild] or SHOW [OPEN] TABLES [FROM db_name] [LIKE wild] or SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] or SHOW INDEX FROM tbl_name [FROM db_name] or SHOW TABLE STATUS [FROM db_name] [LIKE wild] or SHOW STATUS [LIKE wild] or SHOW VARIABLES [LIKE wild] or SHOW LOGS or SHOW [FULL] PROCESSLIST or SHOW GRANTS FOR user or SHOW CREATE TABLE table_name or SHOW MASTER STATUS or SHOW MASTER LOGS or SHOW SLAVE STATUS
SHOW provides information about databases, tables, columns, or
status information about the server. If the LIKE wild part is used,
the wild string can be a string that uses the SQL `%'
and `_' wild-card characters.
You can use db_name.tbl_name as an alternative to the
tbl_name FROM db_name syntax. These two statements are equivalent:
mysql> SHOW INDEX FROM mytable FROM mydb; mysql> SHOW INDEX FROM mydb.mytable;
SHOW DATABASES lists the databases on the MySQL server host. You
can also get this list using the mysqlshow command.
SHOW TABLES lists the tables in a given database. You can also
get this list using the mysqlshow db_name command.
Note: If a user doesn't have any privileges for a table, the
table will not show up in the output from SHOW TABLES or
mysqlshow db_name.
SHOW OPEN TABLES lists the tables that are currently open in the
table cache. See section 5.4.7
How MySQL Opens and Closes Tables. The Comment field tells how
many times the table is cached and in_use.
SHOW COLUMNS lists the columns in a given table. If you specify
the FULL option, you will also get the privileges you have for each
column. If the column types are different than you expect them to be based on a
CREATE TABLE statement, note that MySQL sometimes changes column
types. See section 6.5.3.1
Silent Column Specification Changes.
The DESCRIBE statement provides information similar to
SHOW COLUMNS. See section 6.6.2
DESCRIBE Syntax (Get Information About Columns).
SHOW FIELDS is a synonym for SHOW COLUMNS, and
SHOW KEYS is a synonym for SHOW INDEX. You can also
list a table's columns or indexes with mysqlshow db_name tbl_name
or mysqlshow -k db_name tbl_name.
SHOW INDEX returns the index information in a format that
closely resembles the SQLStatistics call in ODBC. The following
columns are returned:
| Column | Meaning |
Table |
Name of the table. |
Non_unique |
0 if the index can't contain duplicates. |
Key_name |
Name of the index. |
Seq_in_index |
Column sequence number in index, starting with 1. |
Column_name |
Column name. |
Collation |
How the column is sorted in the index. In MySQL, this can have values
`A' (Ascending) or NULL (Not sorted). |
Cardinality |
Number of unique values in the index. This is updated by running
isamchk -a. |
Sub_part |
Number of indexed characters if the column is only partly indexed.
NULL if the entire key is indexed. |
Comment |
Various remarks. For now, it tells whether index is FULLTEXT or not. |
Note that as the Cardinality is counted based on statistics
stored as integers, it's not necessarily accurate for small tables.
SHOW TABLE STATUSSHOW TABLE STATUS [FROM db_name] [LIKE wild]
SHOW TABLE STATUS (new in Version 3.23) works likes SHOW
STATUS, but provides a lot of information about each table. You can also
get this list using the mysqlshow --status db_name command. The
following columns are returned:
| Column | Meaning |
Name |
Name of the table. |
Type |
Type of table. See section 7 MySQL Table Types. |
Row_format |
The row storage format (Fixed, Dynamic, or Compressed). |
Rows |
Number of rows. |
Avg_row_length |
Average row length. |
Data_length |
Length of the data file. |
Max_data_length |
Max length of the data file. |
Index_length |
Length of the index file. |
Data_free |
Number of allocated but not used bytes. |
Auto_increment |
Next autoincrement value. |
Create_time |
When the table was created. |
Update_time |
When the data file was last updated. |
Check_time |
When the table was last checked. |
Create_options |
Extra options used with CREATE TABLE. |
Comment |
The comment used when creating the table (or some information why MySQL couldn't access the table information). |
InnoDB tables will report the free space in the tablespace in
the table comment.
SHOW STATUSSHOW STATUS provides server status
information (like mysqladmin extended-status). The output resembles
that shown below, though the format and numbers probably differ:
+--------------------------+------------+ | Variable_name | Value | +--------------------------+------------+ | Aborted_clients | 0 | | Aborted_connects | 0 | | Bytes_received | 155372598 | | Bytes_sent | 1176560426 | | Connections | 30023 | | Created_tmp_disk_tables | 0 | | Created_tmp_tables | 8340 | | Created_tmp_files | 60 | | Delayed_insert_threads | 0 | | Delayed_writes | 0 | | Delayed_errors | 0 | | Flush_commands | 1 | | Handler_delete | 462604 | | Handler_read_first | 105881 | | Handler_read_key | 27820558 | | Handler_read_next | 390681754 | | Handler_read_prev | 6022500 | | Handler_read_rnd | 30546748 | | Handler_read_rnd_next | 246216530 | | Handler_update | 16945404 | | Handler_write | 60356676 | | Key_blocks_used | 14955 | | Key_read_requests | 96854827 | | Key_reads | 162040 | | Key_write_requests | 7589728 | | Key_writes | 3813196 | | Max_used_connections | 0 | | Not_flushed_key_blocks | 0 | | Not_flushed_delayed_rows | 0 | | Open_tables | 1 | | Open_files | 2 | | Open_streams | 0 | | Opened_tables | 44600 | | Questions | 2026873 | | Select_full_join | 0 | | Select_full_range_join | 0 | | Select_range | 99646 | | Select_range_check | 0 | | Select_scan | 30802 | | Slave_running | OFF | | Slave_open_temp_tables | 0 | | Slow_launch_threads | 0 | | Slow_queries | 0 | | Sort_merge_passes | 30 | | Sort_range | 500 | | Sort_rows | 30296250 | | Sort_scan | 4650 | | Table_locks_immediate | 1920382 | | Table_locks_waited | 0 | | Threads_cached | 0 | | Threads_created | 30022 | | Threads_connected | 1 | | Threads_running | 1 | | Uptime | 80380 | +--------------------------+------------+
The status variables listed above have the following meaning:
| Variable | Meaning |
Aborted_clients |
Number of connections aborted because the client died without closing the connection properly. See section A.2.9 Communication Errors / Aborted Connection. |
Aborted_connects |
Number of tries to connect to the MySQL server that failed. See section A.2.9 Communication Errors / Aborted Connection. |
Bytes_received |
Number of bytes received from all clients. |
Bytes_sent |
Number of bytes sent to all clients. |
Com_xxxx |
Number of times the xxx commands has been executed. |
Connections |
Number of connection attempts to the MySQL server. |
Created_tmp_disk_tables |
Number of implicit temporary tables on disk created while executing statements. |
Created_tmp_tables |
Number of implicit temporary tables in memory created while executing statements. |
Created_tmp_files |
How many temporary files mysqld have created. |
Delayed_insert_threads |
Number of delayed insert handler threads in use. |
Delayed_writes |
Number of rows written with INSERT DELAYED. |
Delayed_errors |
Number of rows written with INSERT DELAYED for which some
error occurred (probably duplicate key). |
Flush_commands |
Number of executed FLUSH commands. |
Handler_delete |
Number of times a row was deleted from a table. |
Handler_read_first |
Number of times the first entry was read from an index. If this is
high, it suggests that the server is doing a lot of full index scans, for
example, SELECT col1 FROM foo, assuming that col1 is indexed.
|
Handler_read_key |
Number of requests to read a row based on a key. If this is high, it is a good indication that your queries and tables are properly indexed. |
Handler_read_next |
Number of requests to read next row in key order. This will be incremented if you are querying an index column with a range constraint. This also will be incremented if you are doing an index scan. |
Handler_read_rnd |
Number of requests to read a row based on a fixed position. This will be high if you are doing a lot of queries that require sorting of the result. |
Handler_read_rnd_next |
Number of requests to read the next row in the datafile. This will be high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have. |
Handler_update |
Number of requests to update a row in a table. |
Handler_write |
Number of requests to insert a row in a table. |
Key_blocks_used |
The number of used blocks in the key cache. |
Key_read_requests |
The number of requests to read a key block from the cache. |
Key_reads |
The number of physical reads of a key block from disk. |
Key_write_requests |
The number of requests to write a key block to the cache. |
Key_writes |
The number of physical writes of a key block to disk. |
Max_used_connections |
The maximum number of connections in use simultaneously. |
Not_flushed_key_blocks |
Keys blocks in the key cache that has changed but hasn't yet been flushed to disk. |
Not_flushed_delayed_rows |
Number of rows waiting to be written in INSERT DELAY
queues. |
Open_tables |
Number of tables that are open. |
Open_files |
Number of files that are open. |
Open_streams |
Number of streams that are open (used mainly for logging). |
Opened_tables |
Number of tables that have been opened. |
Select_full_join |
Number of joins without keys (Should be 0). |
Select_full_range_join |
Number of joins where we used a range search on reference table. |
Select_range |
Number of joins where we used ranges on the first table. (It's normally not critical even if this is big.) |
Select_scan |
Number of joins where we scanned the first table. |
Select_range_check |
Number of joins without keys where we check for key usage after each row (Should be 0). |
Questions |
Number of queries sent to the server. |
Slave_open_temp_tables |
Number of temporary tables currently open by the slave thread |
Slow_launch_threads |
Number of threads that have taken more than
slow_launch_time to connect. |
Slow_queries |
Number of queries that have taken more than
long_query_time. See section 4.9.5
The Slow Query Log. |
Sort_merge_passes |
Number of merges the sort has to do. If this value is large you should
consider increasing sort_buffer. |
Sort_range |
Number of sorts that where done with ranges. |
Sort_rows |
Number of sorted rows. |
Sort_scan |
Number of sorts that where done by scanning the table. |
Table_locks_immediate |
Number of times a table lock was acquired immediately. Available after 3.23.33. |
Table_locks_waited |
Number of times a table lock could not be acquired immediately and a wait was needed. If this is high, and you have performance problems, you should first optimise your queries, and then either split your table(s) or use replication. Available after 3.23.33. |
Threads_cached |
Number of threads in the thread cache. |
Threads_connected |
Number of currently open connections. |
Threads_created |
Number of threads created to handle connections. |
Threads_running |
Number of threads that are not sleeping. |
Uptime |
How many seconds the server has been up. |
Some comments about the above:
Opened_tables is big, then your table_cache
variable is probably too small.
key_reads is big, then your key_cache is
probably too small. The cache hit rate can be calculated with
key_reads/key_read_requests.
Handler_read_rnd is big, then you probably have a lot of
queries that require MySQL to scan whole tables or you have joins that don't
use keys properly.
Threads_created is big, you may want to increase the
thread_cache_size variable. The cache hit rate can be calculated
with Threads_created/Connections.
Created_tmp_disk_tables is big, you may want to increase
the tmp_table_size variable to get the temporary tables memory
based instead of disk based. SHOW VARIABLESSHOW VARIABLES [LIKE wild]
SHOW VARIABLES shows the values of some MySQL system variables.
You can also get this information using the mysqladmin variables
command. If the default values are unsuitable, you can set most of these
variables using command-line options when mysqld starts up. See
section 4.1.1
mysqld Command-line Options.
The output resembles that shown below, though the format and numbers may differ somewhat:
+------------------------------+---------------------------+ | Variable_name | Value | +------------------------------+---------------------------+ | ansi_mode | OFF | | back_log | 50 | | basedir | /my/monty/ | | bdb_cache_size | 16777216 | | bdb_log_buffer_size | 32768 | | bdb_home | /my/monty/data/ | | bdb_max_lock | 10000 | | bdb_logdir | | | bdb_shared_data | OFF | | bdb_tmpdir | /tmp/ | | binlog_cache_size | 32768 | | concurrent_insert | ON | | connect_timeout | 5 | | datadir | /my/monty/data/ | | delay_key_write | ON | | delayed_insert_limit | 100 | | delayed_insert_timeout | 300 | | delayed_queue_size | 1000 | | flush | OFF | | flush_time | 0 | | ft_min_word_len | 4 | | ft_max_word_len | 254 | | ft_max_word_len_for_sort | 20 | | ft_boolean_syntax | + -><()~* | | have_bdb | YES | | have_innodb | YES | | have_raid | YES | | have_openssl | NO | | init_file | | | interactive_timeout | 28800 | | join_buffer_size | 131072 | | key_buffer_size | 16776192 | | language | /my/monty/share/english/ | | large_files_support | ON | | log | OFF | | log_update | OFF | | log_bin | OFF | | log_slave_updates | OFF | | long_query_time | 10 | | low_priority_updates | OFF | | lower_case_table_names | 0 | | max_allowed_packet | 1048576 | | max_binlog_cache_size | 4294967295 | | max_connections | 100 | | max_connect_errors | 10 | | max_delayed_threads | 20 | | max_heap_table_size | 16777216 | | max_join_size | 4294967295 | | max_sort_length | 1024 | | max_tmp_tables | 32 | | max_write_lock_count | 4294967295 | | myisam_bulk_insert_tree_size | 8388608 | | myisam_recover_options | DEFAULT | | myisam_sort_buffer_size | 8388608 | | net_buffer_length | 16384 | | net_read_timeout | 30 | | net_retry_count | 10 | | net_write_timeout | 60 | | open_files_limit | 0 | | pid_file | /my/monty/data/donna.pid | | port | 3306 | | protocol_version | 10 | | record_buffer | 131072 | | query_buffer_size | 0 | | query_cache_limit | 1048576 | | query_cache_size | 16768060 | | query_cache_startup_type | 1 | | safe_show_database | OFF | | server_id | 0 | | skip_locking | ON | | skip_networking | OFF | | skip_show_database | OFF | | slow_launch_time | 2 | | socket | /tmp/mysql.sock | | sort_buffer | 2097116 | | table_cache | 64 | | table_type | MYISAM | | thread_cache_size | 4 | | thread_stack | 65536 | | tmp_table_size | 1048576 | | tmpdir | /tmp/ | | version | 3.23.29a-gamma-debug | | wait_timeout | 28800 | +------------------------------+---------------------------+
Each option is described below. Values for buffer sizes, lengths, and stack
sizes are given in bytes. You can specify values with a suffix of
`K' or `M' to indicate kilobytes or megabytes. For
example, 16M indicates 16 megabytes. The case of suffix letters
does not matter; 16M and 16m are equivalent:
ansi_mode. Is ON if mysqld was
started with --ansi. See section 1.7.2
Running MySQL in ANSI Mode.
back_log The number of outstanding connection requests MySQL
can have. This comes into play when the main MySQL thread gets
very many connection requests in a very short time. It then
takes some time (although very little) for the main thread to check the
connection and start a new thread. The back_log value indicates
how many requests can be stacked during this short time before MySQL
momentarily stops answering new requests. You need to increase this only if
you expect a large number of connections in a short period of time. In other
words, this value is the size of the listen queue for incoming TCP/IP
connections. Your operating system has its own limit on the size of this
queue. The manual page for the Unix listen(2) system call should
have more details. Check your OS documentation for the maximum value for this
variable. Attempting to set back_log higher than your operating
system limit will be ineffective.
basedir The value of the --basedir option.
bdb_cache_size The buffer that is allocated to cache index
and rows for BDB tables. If you don't use BDB
tables, you should start mysqld with --skip-bdb to
not waste memory for this cache.
bdb_log_buffer_size The buffer that is allocated to cache
index and rows for BDB tables. If you don't use BDB
tables, you should set this to 0 or start mysqld with
--skip-bdb to not waste memory for this cache.
bdb_home The value of the --bdb-home option.
bdb_max_lock The maximum number of locks (1000 by default)
you can have active on a BDB table. You should increase this if you get errors
of type bdb: Lock table is out of available locks or Got
error 12 from ... when you have do long transactions or when
mysqld has to examine a lot of rows to calculate the query.
bdb_logdir The value of the --bdb-logdir option.
bdb_shared_data Is ON if you are using
--bdb-shared-data.
bdb_tmpdir The value of the --bdb-tmpdir option.
binlog_cache_size. The size of the cache to hold the SQL
statements for the binary log during a transaction. If you often use big,
multi-statement transactions you can increase this to get more performance.
See section 6.7.1
BEGIN/COMMIT/ROLLBACK Syntax.
character_set The default character set.
character_sets The supported character sets.
concurrent_inserts If ON (the default), MySQL
will allow you to use INSERT on MyISAM tables at the
same time as you run SELECT queries on them. You can turn this
option off by starting mysqld with --safe or
--skip-new.
connect_timeout The number of seconds the mysqld
server is waiting for a connect packet before responding with Bad
handshake.
datadir The value of the --datadir option.
delay_key_write If enabled (is on by default), MySQL will
honor the delay_key_write option CREATE TABLE. This
means that the key buffer for tables with this option will not get flushed on
every index update, but only when a table is closed. This will speed up writes
on keys a lot, but you should add automatic checking of all tables with
myisamchk --fast --force if you use this. Note that if you start
mysqld with the --delay-key-write-for-all-tables
option this means that all tables will be treated as if they were created with
the delay_key_write option. You can clear this flag by starting
mysqld with --skip-new or --safe-mode.
delayed_insert_limit After inserting
delayed_insert_limit rows, the INSERT DELAYED
handler will check if there are any SELECT statements pending. If
so, it allows these to execute before continuing.
delayed_insert_timeout How long a INSERT DELAYED
thread should wait for INSERT statements before terminating.
delayed_queue_size What size queue (in rows) should be
allocated for handling INSERT DELAYED. If the queue becomes full,
any client that does INSERT DELAYED will wait until there is room
in the queue again.
flush This is ON if you have started MySQL with
the --flush option.
flush_time If this is set to a non-zero value, then every
flush_time seconds all tables will be closed (to free up
resources and sync things to disk). We only recommend this option on Win95,
Win98, or on systems where you have very little resources.
ft_min_word_len The minimum length of the word to be included
in a FULLTEXT index. Note: FULLTEXT index
have to be rebuilt after changing this variable.
ft_max_word_len The maximum length of the word to be included
in a FULLTEXT index. Note: FULLTEXT index
have to be rebuilt after changing this variable.
ft_max_word_len_sort The maximum length of the word in a
FULLTEXT index to be used in fast index recreation method in
REPAIR, CREATE INDEX, or ALTER TABLE.
Longer words are inserted the slow way. The rule of the thumb is as follows:
with ft_max_word_len_sort increasing, MySQL will
create bigger temporary files (thus slowing the process down, due to disk
I/O), and will put fewer keys in one sort block (againg, decreasing the
efficiency). When ft_max_word_len_sort is too small, instead,
MySQL will insert a lot of words into index the slow way -
but short words will be inserted very fast. It applies only to index
recreation during REPAIR, CREATE INDEX, or
ALTER TABLE.
ft_boolean_syntax List of operators supported by MATCH
... AGAINST(... IN BOOLEAN MODE). See section 6.8
MySQL Full-text Search.
have_innodb YES if mysqld supports
InnoDB tables. DISABLED if --skip-innodb is used.
have_bdb YES if mysqld supports
Berkeley DB tables. DISABLED if --skip-bdb is used.
have_raid YES if mysqld supports
the RAID option.
have_openssl YES if mysqld supports
SSL (encryption) on the client/server protocol.
init_file The name of the file specified with the
--init-file option when you start the server. This is a file of
SQL statements you want the server to execute when it starts.
interactive_timeout The number of seconds the server waits
for activity on an interactive connection before closing it. An interactive
client is defined as a client that uses the CLIENT_INTERACTIVE
option to mysql_real_connect(). See also
wait_timeout.
join_buffer_size The size of the buffer that is used for full
joins (joins that do not use indexes). The buffer is allocated one time for
each full join between two tables. Increase this value to get a faster full
join when adding indexes is not possible. (Normally the best way to get fast
joins is to add indexes.)
key_buffer_size Index blocks are buffered and are shared by
all threads. key_buffer_size is the size of the buffer used for
index blocks. Increase this to get better index handling (for all reads and
multiple writes) to as much as you can afford; 64M on a 256M machine that
mainly runs MySQL is quite common. If you, however, make this too big (more
than 50% of your total memory?) your system may start to page and become
extremely slow. Remember that because MySQL does not cache data read, that you
will have to leave some room for the OS filesystem cache. You can check the
performance of the key buffer by doing show status and examine
the variables Key_read_requests, Key_reads,
Key_write_requests, and Key_writes. The
Key_reads/Key_read_request ratio should normally be < 0.01.
The Key_write/Key_write_requests is usually near 1 if you are
using mostly updates/deletes but may be much smaller if you tend to do updates
that affect many at the same time or if you are using
delay_key_write. See section 4.5.6
SHOW Syntax. To get even more speed when writing many rows at
the same time, use LOCK TABLES. See section 6.7.2
LOCK TABLES/UNLOCK TABLES Syntax.
language The language used for error messages.
large_file_support If mysqld was compiled with
options for big file support.
locked_in_memory If mysqld was locked in memory
with --memlock
log If logging of all queries is enabled.
log_update If the update log is enabled.
log_bin If the binary log is enabled.
log_slave_updates If the updates from the slave should be
logged.
long_query_time If a query takes longer than this (in
seconds), the Slow_queries counter will be incremented. If you
are using --log-slow-queries, the query will be logged to the
slow query logfile. See section 4.9.5
The Slow Query Log.
lower_case_table_names If set to 1 table names are stored in
lowercase on disk and table names will be case-insensitive. See section 6.1.3
Case Sensitivity in Names.
max_allowed_packet The maximum size of one packet. The
message buffer is initialised to net_buffer_length bytes, but can
grow up to max_allowed_packet bytes when needed. This value by
default is small, to catch big (possibly wrong) packets. You must increase
this value if you are using big BLOB columns. It should be as big
as the biggest BLOB you want to use. The protocol limits for
max_allowed_packet is 16M in MySQL 3.23 and 4G in MySQL 4.0.
max_binlog_cache_size If a multi-statement transaction
requires more than this amount of memory, one will get the error
"Multi-statement transaction required more than 'max_binlog_cache_size' bytes
of storage".
max_binlog_size Available after 3.23.33. If a write to the
binary (replication) log exceeds the given value, rotate the logs. You cannot
set it to less than 1024 bytes, or more than 1 GB. Default is 1 GB.
max_connections The number of simultaneous clients allowed.
Increasing this value increases the number of file descriptors that
mysqld requires. See below for comments on file descriptor
limits. See section A.2.5
Too many connections Error.
max_connect_errors If there is more than this number of
interrupted connections from a host this host will be blocked from further
connections. You can unblock a host with the command FLUSH HOSTS.
max_delayed_threads Don't start more than this number of
threads to handle INSERT DELAYED statements. If you try to insert
data into a new table after all INSERT DELAYED threads are in
use, the row will be inserted as if the DELAYED attribute wasn't
specified.
max_heap_table_size Don't allow creation of heap tables
bigger than this.
max_join_size Joins that are probably going to read more than
max_join_size records return an error. Set this value if your
users tend to perform joins that lack a WHERE clause, that take a
long time, and that return millions of rows.
max_sort_length The number of bytes to use when sorting
BLOB or TEXT values (only the first
max_sort_length bytes of each value are used; the rest are
ignored).
max_user_connections The maximum number of active connections
for a single user (0 = no limit).
max_tmp_tables (This option doesn't yet do anything.) Maximum
number of temporary tables a client can keep open at the same time.
max_write_lock_count After this many write locks, allow some
read locks to run in between.
myisam_bulk_insert_tree_size MySQL uses special tree-like
cache to make bulk inserts (that is, INSERT ... SELECT,
INSERT ... VALUES (...), (...), ..., and LOAD DATA
INFILE) faster. This variable limits the size of the cache tree in
bytes per thread. Setting it to 0 will disable this optimization.
Note: This cache is only used when adding data to non-empty
table. Default value is 8 MB.
myisam_recover_options The value of the
--myisam-recover option.
myisam_sort_buffer_size The buffer that is allocated when
sorting the index when doing a REPAIR or when creating indexes
with CREATE INDEX or ALTER TABLE.
myisam_max_extra_sort_file_size. If the creating of the
temporary file for fast index creation would be this much bigger than using
the key cache, then prefer the key cache method. This is mainly used to force
long character keys in large tables to use the slower key cache method to
create the index. NOTE that this parameter is given in
megabytes!
myisam_max_sort_file_size The maximum size of the temporary
file MySQL is allowed to use while recreating the index (during
REPAIR, ALTER TABLE or LOAD DATA
INFILE. If the file size would be bigger than this, the index will be
created through the key cache (which is slower). NOTE that
this parameter is given in megabytes!
net_buffer_length The communication buffer is reset to this
size between queries. This should not normally be changed, but if you have
very little memory, you can set it to the expected size of a query. (That is,
the expected length of SQL statements sent by clients. If statements exceed
this length, the buffer is automatically enlarged, up to
max_allowed_packet bytes.)
net_read_timeout Number of seconds to wait for more data from
a connection before aborting the read. Note that when we don't expect data
from a connection, the timeout is defined by write_timeout. See
also slave_read_timeout.
net_retry_count If a read on a communication port is
interrupted, retry this many times before giving up. This value should be
quite high on FreeBSD as internal interrupts are sent to all
threads.
net_write_timeout Number of seconds to wait for a block to be
written to a connection before aborting the write.
open_files_limit If this is not 0, then mysqld
will use this value to reserve file descriptors to use with
setrlimit(). If this value is 0 then mysqld will
reserve max_connections*5 or max_connections +
table_cache*2 (whichever is larger) number of files. You should try
increasing this if mysqld gives you the error 'Too many open
files'.
pid_file The value of the --pid-file option.
port The value of the --port option.
protocol_version The protocol version used by the MySQL
server.
record_buffer Each thread that does a sequential scan
allocates a buffer of this size for each table it scans. If you do many
sequential scans, you may want to increase this value.
record_rnd_buffer When reading rows in sorted order after a
sort, the rows are read through this buffer to avoid a disk seeks. If not set,
then it's set to the value of record_buffer.
query_buffer_size The initial allocation of the query buffer.
If most of your queries are long (like when inserting blobs), you should
increase this!
query_cache_limit Don't cache results that are bigger than
this. (Default 1M).
query_cache_size The memory allocated to store results from
old queries. If this is 0, the query cache is disabled (default).
query_cache_startup_type This may be set (only numeric) to
| Value | Alias | Comment |
| 0 | OFF | Don't cache or retrieve results. |
| 1 | ON | Cache all results except SELECT SQL_NO_CACHE ...
queries. |
| 2 | DEMAND | Cache only SELECT SQL_CACHE ... queries.
|
safe_show_databases Don't show databases for which the user
doesn't have any database or table privileges. This can improve security if
you're concerned about people being able to see what databases other users
have. See also skip_show_databases.
server_id The value of the --server-id option.
skip_locking Is OFF if mysqld uses external
locking.
skip_networking Is ON if we only allow local (socket)
connections.
skip_show_databases This prevents people from doing
SHOW DATABASES if they don't have the PROCESS_PRIV
privilege. This can improve security if you're concerned about people being
able to see what databases other users have. See also
safe_show_databases.
slave_read_timeout Number of seconds to wait for more data
from a master/slave connection before aborting the read.
slow_launch_time If creating the thread takes longer than
this value (in seconds), the Slow_launch_threads counter will be
incremented.
socket The Unix socket used by the server.
sort_buffer Each thread that needs to do a sort allocates a
buffer of this size. Increase this value for faster ORDER BY or
GROUP BY operations. See section A.4.4
Where MySQL Stores Temporary Files.
table_cache The number of open tables for all threads.
Increasing this value increases the number of file descriptors that
mysqld requires. You can check if you need to increase the table
cache by checking the Opened_tables variable. See section 4.5.6
SHOW Syntax. If this variable is big and you don't do
FLUSH TABLES a lot (which just forces all tables to be closed and
reopenend), then you should increase the value of this variable. For more
information about the table cache, see section 5.4.7
How MySQL Opens and Closes Tables.
table_type The default table type
thread_cache_size How many threads we should keep in a cache
for reuse. When a client disconnects, the client's threads are put in the
cache if there aren't more than thread_cache_size threads from
before. All new threads are first taken from the cache, and only when the
cache is empty is a new thread created. This variable can be increased to
improve performance if you have a lot of new connections. (Normally this
doesn't give a notable performance improvement if you have a good thread
implementation.) By examing the difference between the
Connections and Threads_created you can see how
efficient the current thread cache is for you.
thread_concurrency On Solaris, mysqld will call
thr_setconcurrency() with this value.
thr_setconcurrency() permits the application to give the threads
system a hint for the desired number of threads that should be run at the same
time.
thread_stack The stack size for each thread. Many of the
limits detected by the crash-me test are dependent on this value.
The default is large enough for normal operation. See section 5.1.4
The MySQL Benchmark Suite.
timezone The timezone for the server.
tmp_table_size If an in-memory temporary table exceeds this
size, MySQL will automatically convert it to an on-disk MyISAM
table. Increase the value of tmp_table_size if you do many
advanced GROUP BY queries and you have lots of memory.
tmpdir The directory used for temporary files and temporary
tables.
version The version number for the server.
wait_timeout The number of seconds the server waits for
activity on a connection before closing it. See also
interactive_timeout. The manual section that describes tuning MySQL contains some information of how to tune the above variables. See section 5.5.2 Tuning Server Parameters.
SHOW LOGSSHOW LOGS shows you status information about existing log files.
It currently only displays information about Berkeley DB log files.
File shows the full path to the log file
Type shows the type of the log file (BDB for
Berkeley DB log files)
Status shows the status of the log file (FREE if
the file can be removed, or IN USE if the file is needed by the
transaction subsystem) SHOW PROCESSLISTSHOW PROCESSLIST shows you which threads are running. You can
also get this information using the mysqladmin processlist command.
If you have the process privilege, you can see all threads.
Otherwise, you can see only your own threads. See section 4.5.5
KILL Syntax. If you don't use the FULL option,
then only the first 100 characters of each query will be shown.
This command is very useful if you get the 'too many connections' error
message and want to find out what's going on. MySQL reserves one extra
connection for a client with the Process_priv privilege to ensure
that you should always be able to login and check the system (assuming you are
not giving this privilege to all your users).
Some frequently states in mysqladmin processlist
Checking table The thread doing an [automatic ?] checking of
the table.
Closing tables Means that the thread is flushing the changed
table data to disk and closing the used tables. This should be a fast
operation. If not, then you should check that you don't have a full disk or
that the disk is not in very heavy use.
Copying to tmp table on disk The temporary result set was
larger than tmp_table_size and the thread is now changing the in
memory based temporary table to a disk based one to save memory.
Creating tmp table The thread is creating a temporary table
to hold a part of the result for the query.
deleting from main table When executing the first part of a
multi-table delete and we are only deleting from the first table.
deleting from reference tables When executing the second part
of a multi-table delete and we are deleting the matched rows from the other
tables.
Flushing tables The thread is executing FLUSH
TABLES and is waiting for all threads to close their tables.
Killed Someone has sent a kill to the thread and it should
abort next time it checks the kill flag. The flag is checked in each major
loop in MySQL, but in some cases it may still take a short time for the thread
to die. If the thread is locked by some other thread, the kill will take
affect as soon as the other thread releases it's lock.
Sending data The thread is processing rows for a
SELECT statement and is also sending data to the client.
Sorting for group The thread is doing a sort to satsify a
GROUP BY.
Sorting for order The thread is doing a sort to satsify a
ORDER BY.
Opening tables This simply means that the thread is trying to
open a table. This is should be very fast procedure, unless something prevents
opening. For example an ALTER TABLE or a LOCK TABLE
can prevent opening a table until the command is finished.
Removing duplicates The query was using SELECT
DISTINCT in such a way that MySQL couldn't optimize that distinct away
at an early stage. Because of this MySQL has to do an extra stage to remove
all duplicated rows before sending the result to the client.
Reopen table The thread got a lock for the table, but noticed
after getting the lock that the underlying table structure changed. It has
freed the lock, closed the table and is now trying to reopen it.
Repair by sorting The repair code is using sorting to create
indexes.
Repair with keycache The repair code is using creating keys
one by one through the key cache. This is much slower than Repair by
sorting.
Searching rows for update The thread is doing a first phase
to find all matching rows before updating them. This has to be done if the
UPDATE is changing the index that is used to find the involved
rows.
Sleeping The thread is wating for the client to send a new
command to it.
System lock The thread is waiting for getting to get a
external system lock for the table. If you are not using multiple mysqld
servers that are accessing the same tables, you can disable system locks with
the --skip-locking option.
Upgrading lock The INSERT DELAYED handler is
trying to get a lock for the table to insert rows.
Updating The thread is searching for rows to update and
updating them.
User Lock The thread is waiting on a GET_LOCK().
Waiting for tables The thread got a notification that the
underlying structure for a table has changed and it needs to reopen the table
to get the new structure. To be able to reopen the table it must however wait
until all other threads have closed the table in question. This notification
happens if another thread has used FLUSH TABLES or one of the
following commands on the table in question: FLUSH TABLES
table_name, ALTER TABLE, RENAME TABLE,
REPAIR TABLE, ANALYZE TABLE or OPTIMIZE
TABLE.
waiting for handler insert The INSERT DELAYED
handler has processed all inserts and are waiting to get new ones. Most states are very quick operations. If threads last in any of these states for many seconds, there may be a problem around that needs to be investigated.
There are some other states that are not mentioned above, but most of these
are only useful to find bugs in mysqld.
SHOW GRANTSSHOW GRANTS FOR user lists the grant commands that must be
issued to duplicate the grants for a user.
mysql> SHOW GRANTS FOR root@localhost; +---------------------------------------------------------------------+ | Grants for root@localhost | +---------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION | +---------------------------------------------------------------------+
SHOW CREATE TABLEShows a CREATE TABLE statement that will create the given table:
mysql> show create table t\G
*************************** 1. row ***************************
Table: t
Create Table: CREATE TABLE t (
id int(11) default NULL auto_increment,
s char(60) default NULL,
PRIMARY KEY (id)
) TYPE=MyISAM
SHOW CREATE TABLE will quote table and column names according to
SQL_QUOTE_SHOW_CREATE option. section 5.5.6
SET Syntax.
By default, MySQL uses the ISO-8859-1 (Latin1) character set with sorting according to Swedish/Finnish. This is the character set suitable in the USA and western Europe.
All standard MySQL binaries are compiled with
--with-extra-charsets=complex. This will add code to all standard
programs to be able to handle latin1 and all multi-byte character
sets within the binary. Other character sets will be loaded from a character-set
definition file when needed.
The character set determines what characters are allowed in names and how
things are sorted by the ORDER BY and GROUP BY clauses
of the SELECT statement.
You can change the character set with the
--default-character-set option when you start the server. The
character sets available depend on the --with-charset=charset and
--with-extra-charset= list-of-charset | complex | all options to
configure, and the character set configuration files listed in
`SHAREDIR/charsets/Index'. See section 2.3.3
Typical configure Options.
If you change the character set when running MySQL (which may also change the sort order), you must run myisamchk -r -q on all tables. Otherwise your indexes may not be ordered correctly.
When a client connects to a MySQL server, the server sends the default character set in use to the client. The client will switch to use this character set for this connection.
One should use mysql_real_escape_string() when escaping strings
for a SQL query. mysql_real_escape_string() is identical to the old
mysql_escape_string() function, except that it takes the
MYSQL connection handle as the first parameter.
If the client is compiled with different paths than where the server is installed and the user who configured MySQL didn't included all character sets in the MySQL binary, one must specify for the client where it can find the additional character sets it will need if the server runs with a different character set than the client.
One can specify this by putting in a MySQL option file:
[client] character-sets-dir=/usr/local/mysql/share/mysql/charsets
where the path points to where the dynamic MySQL character sets are stored.
One can force the client to use specific character set by specifying:
[client] default-character-set=character-set-name
but normally this is never needed.
To get German sorting order, you should start mysqld with
--default-character-set=latin_de. This will give you the following
characteristics.
When sorting and comparing string's the following mapping is done on the strings before doing the comparison:
ä -> ae ö -> oe ü -> ue ß -> ss
All accented characters, are converted to their un-accented uppercase counterpart. All letters are converted to uppercase.
When comparing strings with LIKE the one -> two character
mapping is not done. All letters are converted to uppercase. Accent are removed
from all letters except: Ü, ü, Ö,
ö, Ä and ä.
mysqld can issue error messages in the following languages:
Czech, Danish, Dutch, English (the default), Estonian, French, German, Greek,
Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish,
Portuguese, Romanian, Russian, Slovak, Spanish, and Swedish.
To start mysqld with a particular language, use either the
--language=lang or -L lang options. For example:
shell> mysqld --language=swedish
or:
shell> mysqld --language=/usr/local/share/swedish
Note that all language names are specified in lowercase.
The language files are located (by default) in `mysql_base_dir/share/LANGUAGE/'.
To update the error message file, you should edit the `errmsg.txt' file and execute the following command to generate the `errmsg.sys' file:
shell> comp_err errmsg.txt errmsg.sys
If you upgrade to a newer version of MySQL, remember to repeat your changes with the new `errmsg.txt' file.
To add another character set to MySQL, use the following procedure.
Decide if the set is simple or complex. If the character set does not need to use special string collating routines for sorting and does not need multi-byte character support, it is simple. If it needs either of those features, it is complex.
For example, latin1 and danish are simple
charactersets while big5 or czech are complex
character sets.
In the following section, we have assumed that you name your character set
MYSET.
For a simple character set do the following:
ctype array takes up the first 257 words. The
to_lower, to_upper and sort_order
arrays take up 256 words each after that. CHARSETS_AVAILABLE and
COMPILED_CHARSETS lists in configure.in.
For a complex character set do the following:
ctype_MYSET,
to_lower_MYSET, and so on. This corresponds to the arrays in the
simple character set. See section 4.6.4
The character definition arrays. For a complex character set
/* * This comment is parsed by configure to create ctype.c, * so don't change it unless you know what you are doing. * * .configure. number_MYSET=MYNUMBER * .configure. strxfrm_multiply_MYSET=N * .configure. mbmaxlen_MYSET=N */The
configure program uses this comment to include the
character set into the MySQL library automatically. The strxfrm_multiply and
mbmaxlen lines will be explained in the following sections. Only include them
if you the string collating functions or the multi-byte character set
functions, respectively.
my_strncoll_MYSET()
my_strcoll_MYSET()
my_strxfrm_MYSET()
my_like_range_MYSET() CHARSETS_AVAILABLE and
COMPILED_CHARSETS lists in configure.in.
The file `sql/share/charsets/README' includes some more instructions.
If you want to have the character set included in the MySQL distribution, mail a patch to internals@lists.mysql.com.
to_lower[] and to_upper[] are simple arrays that
hold the lowercase and uppercase characters corresponding to each member of the
character set. For example:
to_lower['A'] should contain 'a' to_upper['a'] should contain 'A'
sort_order[] is a map indicating how characters should be
ordered for comparison and sorting purposes. For many character sets, this is
the same as to_upper[] (which means sorting will be case
insensitive). MySQL will sort characters based on the value of
sort_order[character]. For more complicated sorting rules, see the
discussion of string collating below. See section 4.6.5
String Collating Support.
ctype[] is an array of bit values, with one element for one
character. (Note that to_lower[], to_upper[], and
sort_order[] are indexed by character value, but
ctype[] is indexed by character value + 1. This is an old legacy to
be able to handle EOF.)
You can find the following bitmask definitions in `m_ctype.h':
#define _U 01 /* Uppercase */ #define _L 02 /* Lowercase */ #define _N 04 /* Numeral (digit) */ #define _S 010 /* Spacing character */ #define _P 020 /* Punctuation */ #define _C 040 /* Control character */ #define _B 0100 /* Blank */ #define _X 0200 /* heXadecimal digit */
The ctype[] entry for each character should be the union of the
applicable bitmask values that describe the character. For example,
'A' is an uppercase character (_U) as well as a
hexadecimal digit (_X), so ctype['A'+1] should contain
the value:
_U + _X = 01 + 0200 = 0201
If the sorting rules for your language are too complex to be handled with the
simple sort_order[] table, you need to use the string collating
functions.
Right now the best documentation on this is the character sets that are already implemented. Look at the big5, czech, gbk, sjis, and tis160 character sets for examples.
You must specify the strxfrm_multiply_MYSET=N value in the
special comment at the top of the file. N should be set to the
maximum ratio the strings may grow during my_strxfrm_MYSET (it must
be a positive integer).
If your want to add support for a new character set that includes multi-byte characters, you need to use the multi-byte character functions.
Right now the best documentation on this is the character sets that are
already implemented. Look at the euc_kr, gb2312, gbk, sjis and ujis character
sets for examples. These are implemented in the ctype-'charset'.c
files in the `strings' directory.
You must specify the mbmaxlen_MYSET=N value in the special
comment at the top of the source file. N should be set to the size
in bytes of the largest character in the set.
If you try to use a character set that is not compiled into your binary, you can run into a couple of different problems:
--character-sets-dir option to the program in
question.
ERROR 1105: File '/usr/local/share/mysql/charsets/?.conf' not found (Errcode: 2)In this case you should either get a new
Index file or add
by hand the name of any missing character sets. For MyISAM tables, you can check the character set name and number for a
table with myisamchk -dvv table_name.
All MySQL clients that communicate with the server using the
mysqlclient library use the following environment variables:
| Name | Description |
MYSQL_UNIX_PORT |
The default socket; used for connections to localhost
|
MYSQL_TCP_PORT |
The default TCP/IP port |
MYSQL_PWD |
The default password |
MYSQL_DEBUG |
Debug-trace options when debugging |
TMPDIR |
The directory where temporary tables/files are created |
Use of MYSQL_PWD is insecure. See section 4.2.7
Connecting to the MySQL Server.
The
`mysql' client uses the file named in the MYSQL_HISTFILE
environment variable to save the command-line history. The default value for the
history file is `$HOME/.mysql_history', where $HOME is the
value of the HOME environment variable. See section F
Environment Variables.
All MySQL programs take many different options. However, every MySQL program
provides a --help option that you can use to get a full description
of the program's different options. For example, try mysql --help.
You can override default options for all standard client programs with an option file. section 4.1.2 my.cnf Option Files.
The list below briefly describes the MySQL programs:
myisamchk
myisamchk has many functions, it is described in
its own chapter. See section 4
MySQL Database Administration.
make_binary_distribution
support.mysql.com for the
convenience of other MySQL users.
msql2mysql
mSQL programs to MySQL. It
doesn't handle all cases, but it gives a good start when converting.
mysqlaccess
mysqladmin
mysqladmin can also be used to retrieve
version, process, and status information from the server. See section 4.8.3
mysqladmin, Administrating a MySQL Server.
mysqlbug
mysqld
mysqldump
mysqlimport
LOAD DATA
INFILE. See section 4.8.7
mysqlimport, Importing Data from Text Files.
mysqlshow
mysql_install_db
replace
msql2mysql, but that has
more general applicability as well. replace changes strings in
place in files or on the standard input. Uses a finite state machine to match
longer strings first. Can be used to swap strings. For example, this command
swaps a and b in the given files: shell> replace a b b a -- file1 file2 ...
safe_mysqld is the recommended way to start a
mysqld daemon on Unix. safe_mysqld adds some safety
features such as restarting the server when an error occurs and logging run-time
information to a log file.
If you don't use --mysqld=# or --mysqld-version=#
safe_mysqld will use an executable named mysqld-max if
it exists. If not, safe_mysqld will start mysqld. This
makes it very easy to test to use mysqld-max instead of
mysqld; Just copy mysqld-max to where you have
mysqld and it will be used.
Normally one should never edit the safe_mysqld script, but
instead put the options to safe_mysqld in the
[safe_mysqld] section in the my.cnf file.
safe_mysqld will read all options from the [mysqld],
[server] and [safe_mysqld] sections from the option
files. See section 4.1.2
my.cnf Option Files.
Note that all options on the command line to safe_mysqld are
passed to mysqld. If you wants to use any options in
safe_mysqld that mysqld doesn't support, you must
specify these in the option file.
Most of the options to safe_mysqld are the same as the options
to mysqld. See section 4.1.1
mysqld Command-line Options.
safe_mysqld supports the following options:
mysqld should be
able to create. Passed to ulimit -c.
mysqld
mysqld version in the
ledir directory you want to start.
--mysqld= but here you
only give the suffix for mysqld. For example if you use
--mysqld-version=max, safe_mysqld will start the
ledir/mysqld-max version. If the argument to
--mysqld-version is empty, ledir/mysqld will be
used.
mysqld should be able to
open. Passed to ulimit -n. Note that you need to start
safe_mysqld as root for this to work properly!
TZ) variable to the value
of this parameter.
The safe_mysqld script is written so that it normally is able to
start a server that was installed from either a source or a binary version of
MySQL, even if these install the server in slightly different locations.
safe_mysqld expects one of these conditions to be true:
safe_mysqld is invoked. safe_mysqld looks under its
working directory for `bin' and `data' directories (for
binary distributions) or for `libexec' and `var' directories
(for source distributions). This condition should be met if you execute
safe_mysqld from your MySQL installation directory (for example,
`/usr/local/mysql' for a binary distribution).
safe_mysqld attempts to locate them by absolute
pathnames. Typical locations are `/usr/local/libexec' and
`/usr/local/var'. The actual locations are determined when the
distribution was built from which safe_mysqld comes. They should
be correct if MySQL was installed in a standard location. Because safe_mysqld will try to find the server and databases
relative to its own working directory, you can install a binary distribution of
MySQL anywhere, as long as you start safe_mysqld from the MySQL
installation directory:
shell> cd mysql_installation_directory shell> bin/safe_mysqld &
If safe_mysqld fails, even when invoked from the MySQL
installation directory, you can modify it to use the path to mysqld
and the pathname options that are correct for your system. Note that if you
upgrade MySQL in the future, your modified version of safe_mysqld
will be overwritten, so you should make a copy of your edited version that you
can reinstall.
mysqld_multi is meant for managing several mysqld
processes running in different Unix sockets and TCP/IP ports.
The program will search for group(s) named [mysqld#] from my.cnf (or the
given --config-file=...), where # can be any positive number starting from 1.
These groups should be the same as the usual [mysqld] group (e.g.
options to mysqld, see MySQL manual for detailed information about this group),
but with those port, socket etc. options that are wanted for each separate
mysqld processes. The number in the group name has another
function; it can be used for starting, stopping, or reporting some specific
mysqld servers with this program. See the usage and options below
for more information.
Usage: mysqld_multi [OPTIONS] {start|stop|report} [GNR,GNR,GNR...]
or mysqld_multi [OPTIONS] {start|stop|report} [GNR-GNR,GNR,GNR-GNR,...]
The GNR above means the group number. You can start, stop or report any GNR, or several of them at the same time. (See --example) The GNRs list can be comma separated, or a dash combined, of which the latter means that all the GNRs between GNR1-GNR2 will be affected. Without GNR argument all the found groups will be either started, stopped, or reported. Note that you must not have any white spaces in the GNR list. Anything after a white space is ignored.
mysqld_multi supports the following options:
[mysqld_multi]), but only groups [mysqld#]. Without this option
everything will be searched from the ordinary my.cnf file.
mysqladmin binary to be used for a server
shutdown.
mysqld binary to be used. Note that you can give
safe_mysqld to this option also. The options are passed to
mysqld. Just make sure you have mysqld in your
environment variable PATH or fix safe_mysqld.
mysqladmin.
mysqladmin.
Some notes about mysqld_multi:
mysqld
services (e.g using the mysqladmin) have the same password and
username for all the data directories accessed (to the 'mysql' database) And
make sure that the user has the 'Shutdown_priv' privilege! If you have many
data- directories and many different 'mysql' databases with different
passwords for the MySQL 'root' user, you may want to create a common
'multi_admin' user for each using the same password (see below). Example how
to do it: shell> mysql -u root -S /tmp/mysql.sock -proot_password -e "GRANT SHUTDOWN ON *.* TO multi_admin@localhost IDENTIFIED BY 'multipass'" See section 4.2.5 How the Privilege System Works.You will have to do the above for each
mysqld running in
each data directory, that you have (just change the socket, -S=...).
pid-file is very important, if you are using
safe_mysqld to start mysqld (e.g.
--mysqld=safe_mysqld) Every mysqld should have its own
pid-file. The advantage using safe_mysqld instead of
mysqld directly here is, that safe_mysqld 'guards'
every mysqld process and will restart it, if a
mysqld process fails due to signal kill -9, or similar. (Like
segmentation fault, which MySQL should never do, of course ;) Please note that
safe_mysqld script may require that you start it from a certain
place. This means that you may have to cd to a certain directory,
before you start the mysqld_multi. If you have problems starting,
please see the safe_mysqld script. Check especially the lines: -------------------------------------------------------------------------- MY_PWD=`pwd` Check if we are starting this relative (for the binary release) if test -d /data/mysql -a -f ./share/mysql/english/errmsg.sys -a -x ./bin/mysqld -------------------------------------------------------------------------- See section 4.7.2 safe_mysqld, the wrapper around mysqld.The above test should be successful, or you may encounter problems.
mysqlds in the same
data directory. Use separate data directories, unless you
know what you are doing!
mysqld.
mysqld group were intentionally left out
from the example. You may have 'gaps' in the config file. This gives you more
flexibility. The order in which the mysqlds are started or
stopped depends on the order in which they appear in the config file.
mysqld, but in order
to do this you need to be root when you start the mysqld_multi
script. Having the option in the config file doesn't matter; you will just get
a warning, if you are not the superuser and the mysqlds are
started under your Unix account. Important:
Make sure that the pid-file and the data directory are
read+write(+execute for the latter one) accessible for that
Unix user, who the specific mysqld process is started as.
Do not use the Unix root account for this, unless you
know what you are doing!
mysqlds and
why one would want to have separate mysqld
processes. Starting multiple mysqlds in one data directory
will not give you extra performance in a threaded system!
See section 4.1.4 Running Multiple MySQL Servers on the Same Machine.
This is an example of the config file on behalf of mysqld_multi.
# This file should probably be in your home dir (~/.my.cnf) or /etc/my.cnf # Version 2.1 by Jani Tolonen [mysqld_multi] mysqld = /usr/local/bin/safe_mysqld mysqladmin = /usr/local/bin/mysqladmin user = multi_admin password = multipass [mysqld2] socket = /tmp/mysql.sock2 port = 3307 pid-file = /usr/local/mysql/var2/hostname.pid2 datadir = /usr/local/mysql/var2 language = /usr/local/share/mysql/english user = john [mysqld3] socket = /tmp/mysql.sock3 port = 3308 pid-file = /usr/local/mysql/var3/hostname.pid3 datadir = /usr/local/mysql/var3 language = /usr/local/share/mysql/swedish user = monty [mysqld4] socket = /tmp/mysql.sock4 port = 3309 pid-file = /usr/local/mysql/var4/hostname.pid4 datadir = /usr/local/mysql/var4 language = /usr/local/share/mysql/estonia user = tonu [mysqld6] socket = /tmp/mysql.sock6 port = 3311 pid-file = /usr/local/mysql/var6/hostname.pid6 datadir = /usr/local/mysql/var6 language = /usr/local/share/mysql/japanese user = jani
See section 4.1.2 my.cnf Option Files.
myisampack is used to compress MyISAM tables, and
pack_isam is used to compress ISAM tables. Because ISAM tables are
deprecated, we will only discuss myisampack here, but everything
said about myisampack should also be true for
pack_isam.
myisampack works by compressing each column in the table
separately. The information needed to decompress columns is read into memory
when the table is opened. This results in much better performance when accessing
individual records, because you only have to uncompress exactly one record, not
a much larger disk block as when using Stacker on MS-DOS. Usually,
myisampack packs the data file 40%-70%.
MySQL uses memory mapping (mmap()) on compressed tables and
falls back to normal read/write file usage if mmap() doesn't work.
There are currently two limitations with myisampack:
myisampack can also pack BLOB or
TEXT columns. The older pack_isam could not do this.
Fixing these limitations is on our TODO list but with low priority.
myisampack is invoked like this:
shell> myisampack [options] filename ...
Each filename should be the name of an index (`.MYI') file. If you are not in the database directory, you should specify the pathname to the file. It is permissible to omit the `.MYI' extension.
myisampack supports the following options:
tbl_name.OLD.
debug_options
string often is 'd:t:o,filename'.
myisampack creates a temporary file named
`tbl_name.TMD' while it compresses the table. If you kill
myisampack, the `.TMD' file may not be deleted.
Normally, myisampack exits with an error if it finds that
`tbl_name.TMD' exists. With --force,
myisampack packs the table anyway.
big_tbl_name. All tables that are to be
combined must be identical (same column names and types, same
indexes, etc.).
myisampack stores all rows with
length pointers of 1, 2, or 3 bytes. In most normal cases,
myisampack can determine the right length value before it begins
packing the file, but it may notice during the packing process that it could
have used a shorter length. In this case, myisampack will print a
note that the next time you pack the same file, you could use a shorter record
length.)
mysqld
server was invoked with the --skip-locking option, it is not a
good idea to invoke myisampack if the table might be updated
during the packing process. The sequence of commands shown below illustrates a typical table compression session:
shell> ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 53248 Apr 17 19:00 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-02-02 3:06:43 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafile pointer (bytes): 2 Keyfile pointer (bytes): 2 Max datafile length: 54657023 Max keyfile length: 33554431 Recordlength: 834 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip. text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 shell> myisampack station.MYI Compressing station.MYI: (1192 records) - Calculating statistics normal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space: 0 end-space: 12 table-lookups: 5 zero: 7 Original trees: 57 After join: 17 - Compressing file 87.14% shell> ls -l station.* -rw-rw-r-- 1 monty my 127874 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 55296 Apr 17 19:04 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-04-17 19:04:26 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 1 Max datafile length: 16777215 Max keyfile length: 131071 Recordlength: 834 Record format: Compressed table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip. text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lookup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 always zero 2 9 21 336 4 always zero 2 9 22 340 1 3 9 23 341 8 table-lookup 9 0 24 349 8 table-lookup 10 0 25 357 8 always zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lookup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 always zero 2 9 34 392 4 table-lookup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 always zero 2 9 40 413 4 no zeros 2 9 41 417 4 always zero 2 9 42 421 4 no zeros 2 9 43 425 4 always zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9
The information printed by myisampack is described below:
normal
empty-space
empty-zero
empty-fill
INTEGER column may be changed to MEDIUMINT).
pre-space
end-space
table-lookup
ENUM before Huffman compression.
zero
Original trees
After join
After a table has been compressed, myisamchk -dvv prints
additional information about each field:
Type
constant
no endspace
no endspace, not_always
no endspace, no empty
table-lookup
ENUM.
zerofill(n)
n bytes in the value are always 0 and
are not stored.
no zeros
always zero
Huff tree
Bits
After you have run pack_isam/myisampack you must
run isamchk/myisamchk to re-create the index. At this
time you can also sort the index blocks and create statistics needed for the
MySQL optimiser to work more efficiently:
myisamchk -rq --analyze --sort-index table_name.MYI isamchk -rq --analyze --sort-index table_name.ISM
After you have installed the packed table into the MySQL database directory
you should do mysqladmin flush-tables to force mysqld
to start using the new table.
If you want to unpack a packed table, you can do this with the
--unpack option to isamchk or myisamchk.
mysqld-max is the MySQL server (mysqld) configured
with the following configure options:
| Option | Comment |
| --with-server-suffix=-max | Add a suffix to the mysqld version string. |
| --with-innodb | Support for InnoDB tables. |
| --with-bdb | Support for Berkeley DB (BDB) tables |
| CFLAGS=-DUSE_SYMDIR | Symbolic links support for Windows. |
You can find the MySQL-max binaries at http://mysql.com/downloads/mysql-max-3.23.html.
The Windows MySQL 3.23 binary distribution includes both the standard
mysqld.exe binary and the mysqld-max.exe binary. http://mysql.com/downloads/mysql-3.23.html.
See section 2.1.2
Installing MySQL on Windows.
Note that as InnoDB and Berkeley DB are not available for all platforms, some
of the Max binaries may not have support for both of these. You can
check which table types are supported by doing the following query:
mysql> show variables like "have_%"; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | have_bdb | YES | | have_innodb | NO | | have_isam | YES | | have_raid | NO | | have_openssl | NO | +---------------+-------+
The meaning of the values are:
| Value | Meaning. |
YES |
The option is activated and usable. |
NO |
MySQL is not compiled with support for this option. |
DISABLED |
The xxxx option is disabled because one started mysqld
with --skip-xxxx or because one didn't start
mysqld with all needed options to enable the option. In this
case the hostname.err file should contain a reason for why
the option is disabled. |
Note: To be able to create InnoDB tables you
must edit your startup options to include at least the
innodb_data_file_path option. See section 7.5.2
InnoDB Startup Options.
To get better performance for BDB tables, you should add some configuration options for these too. See section 7.6.3 BDB startup options.
safe_mysqld will automatically try to start any
mysqld binary with the -max prefix. This makes it very
easy to test out a another mysqld binary in an existing
installation. Just run configure with the options you want and then
install the new mysqld binary as mysqld-max in the
same directory where your old mysqld binary is. See section 4.7.2
safe_mysqld, the wrapper around mysqld.
The mysqld-max RPM uses the above mentioned
safe_mysqld feature. It just installs the mysqld-max
executable and safe_mysqld will automatically use this executable
when safe_mysqld is restarted.
The following table shows which table types our standard MySQL-Max binaries includes:
| System | BDB | InnoDB |
| AIX 4.3 | N | Y |
| HP-UX 11.0 | N | Y |
| Linux-Alpha | N | Y |
| Linux-Intel | Y | Y |
| Linux-Ia64 | N | Y |
| Solaris-intel | N | Y |
| Solaris-sparc | Y | Y |
| SCO OSR5 | Y | Y |
| UnixWare | Y | Y |
| Windows/NT | Y | Y |
All MySQL clients that communicate with the server using the
mysqlclient library use the following environment variables:
| Name | Description |
MYSQL_UNIX_PORT |
The default socket; used for connections to localhost
|
MYSQL_TCP_PORT |
The default TCP/IP port |
MYSQL_PWD |
The default password |
MYSQL_DEBUG |
Debug-trace options when debugging |
TMPDIR |
The directory where temporary tables/files are created |
Use of MYSQL_PWD is insecure. See section 4.2.7
Connecting to the MySQL Server.
The
`mysql' client uses the file named in the MYSQL_HISTFILE
environment variable to save the command-line history. The default value for the
history file is `$HOME/.mysql_history', where $HOME is the
value of the HOME environment variable. See section F
Environment Variables.
All MySQL programs take many different options. However, every MySQL program
provides a --help option that you can use to get a full description
of the program's different options. For example, try mysql --help.
You can override default options for all standard client programs with an option file. section 4.1.2 my.cnf Option Files.
The list below briefly describes the MySQL programs:
myisamchk
myisamchk has many functions, it is described in
its own chapter. See section 4
MySQL Database Administration.
make_binary_distribution
support.mysql.com for the
convenience of other MySQL users.
msql2mysql
mSQL programs to MySQL. It
doesn't handle all cases, but it gives a good start when converting.
mysqlaccess
mysqladmin
mysqladmin can also be used to retrieve
version, process, and status information from the server. See section 4.8.3
mysqladmin, Administrating a MySQL Server.
mysqlbug
mysqld
mysqldump
mysqlimport
LOAD DATA
INFILE. See section 4.8.7
mysqlimport, Importing Data from Text Files.
mysqlshow
mysql_install_db
replace
msql2mysql, but that has
more general applicability as well. replace changes strings in
place in files or on the standard input. Uses a finite state machine to match
longer strings first. Can be used to swap strings. For example, this command
swaps a and b in the given files: shell> replace a b b a -- file1 file2 ...
mysql is a simple SQL shell (with GNU readline
capabilities). It supports interactive and non-interactive use. When used
interactively, query results are presented in an ASCII-table format. When used
non-interactively (for example, as a filter), the result is presented in
tab-separated format. (The output format can be changed using command-line
options.) You can run scripts simply like this:
shell> mysql database < script.sql > output.tab
If you have problems due to insufficient memory in the client, use the
--quick option! This forces mysql to use
mysql_use_result() rather than mysql_store_result() to
retrieve the result set.
Using mysql is very easy. Just start it as follows: mysql
database or mysql --user=user_name --password=your_password
database. Type a SQL statement, end it with `;',
`\g', or `\G' and press Enter.
mysql supports the following options:
-?, --help
-A, --no-auto-rehash
-B, --batch
--character-sets-dir=...
-C, --compress
-#, --debug[=...]
-D, --database=...
my.cnf file.
--default-character-set=...
-e, --execute=...
-E, --vertical
\G.
-f, --force
-g, --no-named-commands
-G, --enable-named-commands
-i, --ignore-space
-h, --host=...
-H, --html
-L, --skip-line-numbers
--no-pager
--no-tee
-n, --unbuffered
-N, --skip-column-names
-O, --set-variable var=option
--help lists variables.
-o, --one-database
--pager[=...]ENV variable PAGER.
Valid pagers are less, more, cat [> filename], etc. See interactive help
(\h) also. This option does not work in batch mode. Pager works only in Unix.
-p[password], --password[=...]
-p you can't have a space between the option and the
password.
-P --port=...
-q, --quick
-r, --raw
--batch
-s, --silent
-S --socket=...
-t --table
-T, --debug-info
--tee=...
-u, --user=#
-U, --safe-updates[=#], --i-am-a-dummy[=#]
UPDATE and DELETE that uses keys. See
below for more information about this option. You can reset this option if you
have it in your my.cnf file by using
--safe-updates=0.
-v, --verbose
-V, --version
-w, --wait
You can also set the following variables with -O or
--set-variable:
| Variable Name | Default | Description |
| connect_timeout | 0 | Number of seconds before timeout connection. |
| max_allowed_packet | 16777216 | Max packetlength to send/receive from to server |
| net_buffer_length | 16384 | Buffer for TCP/IP and socket communication |
| select_limit | 1000 | Automatic limit for SELECT when using --i-am-a-dummy |
| max_join_size | 1000000 | Automatic limit for rows in a join when using --i-am-a-dummy. |
If you type 'help' on the command line, mysql will print out the
commands that it supports:
mysql> help MySQL commands: help (\h) Display this text. ? (\h) Synonym for `help'. clear (\c) Clear command. connect (\r) Reconnect to the server. Optional arguments are db and host. edit (\e) Edit command with $EDITOR. ego (\G) Send command to mysql server, display result vertically. exit (\q) Exit mysql. Same as quit. go (\g) Send command to mysql server. nopager (\n) Disable pager, print to stdout. notee (\t) Don't write into outfile. pager (\P) Set PAGER [to_pager]. Print the query results via PAGER. print (\p) Print current command. quit (\q) Quit mysql. rehash (\#) Rebuild completion hash. source (\.) Execute a SQL script file. Takes a file name as an argument. status (\s) Get status information from the server. tee (\T) Set outfile [to_outfile]. Append everything into given outfile. use (\u) Use another database. Takes database name as argument.
From the above, pager only works in Unix.
The status command gives you some information
about the connection and the server you are using. If you are running in the
--safe-updates mode, status will also print the values
for the mysql variables that affect your queries.
A useful startup option for beginners (introduced in MySQL
Version 3.23.11) is --safe-updates (or --i-am-a-dummy
for users that has at some time done a DELETE FROM table_name but
forgot the WHERE clause). When using this option,
mysql sends the following command to the MySQL server when opening
the connection:
SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=#select_limit#,
SQL_MAX_JOIN_SIZE=#max_join_size#"
where #select_limit# and #max_join_size# are
variables that can be set from the mysql command line. See section
5.5.6
SET Syntax.
The effect of the above is:
UPDATE or DELETE
statement if you don't have a key constraint in the WHERE part.
One can, however, force an UPDATE/DELETE by using
LIMIT: UPDATE table_name SET not_key_column=# WHERE not_key_column=# LIMIT 1;
#select_limit#
rows.
SELECT's that will probably need to examine more than
#max_join_size row combinations will be aborted. Some useful hints about the mysql client:
Some data is much more readable when displayed vertically, instead of the usual horizontal box type output. For example longer text, which includes new lines, is often much easier to be read with vertical output.
mysql> select * from mails where length(txt) < 300 limit 300,1\G
*************************** 1. row ***************************
msg_nro: 3068
date: 2000-03-01 23:29:50
time_zone: +0200
mail_from: Monty
reply: monty@no.spam.com
mail_to: "Thimble Smith" <tim@no.spam.com>
sbj: UTF-8
txt: >>>>> "Thimble" == Thimble Smith writes:
Thimble> Hi. I think this is a good idea. Is anyone familiar with UTF-8
Thimble> or Unicode? Otherwise I'll put this on my TODO list and see what
Thimble> happens.
Yes, please do that.
Regards,
Monty
file: inbox-jani-1
hash: 190402944
1 row in set (0.09 sec)
tee option. The tee
can be started with option --tee=..., or from the command line
interactively with command tee. All the data displayed on the
screen will also be appended into a given file. This can be very useful for
debugging purposes also. The tee can be disabled from the command
line with command notee. Executing tee again starts
logging again. Without a parameter the previous file will be used. Note that
tee will flush the results into the file after each command, just
before the command line appears again waiting for the next command.
--pager[=...]. Without argument, mysql client will
look for environment variable PAGER and set pager to that.
pager can be started from the interactive command line with
command pager and disabled with command nopager. The
command takes an argument optionally and the pager will be set to
that. Command pager can be called without an argument, but this
requires that the option --pager was used, or the
pager will default to stdout. pager works only in
Unix, since it uses the popen() function, which doesn't exist in Windows. In
Windows, the tee option can be used instead, although it may not
be as handy as pager can be in some situations.
pager: You can use it to write to a file: mysql> pager cat > /tmp/log.txtand the results will only go to a file. You can also pass any options for the programs that you want to use with the
pager: mysql> pager less -n -i -SFrom the above do note the option '-S'. You may find it very useful when browsing the results; try the option with horizontal output (end commands with '\g', or ';') and with vertical output (end commands with '\G'). Sometimes a very wide result set is hard to be read from the screen, with option -S to less you can browse the results within the interactive less from left to right, preventing lines longer than your screen from being continued to the next line. This can make the result set much more readable. You can swith the mode between on and off within the interactive less with '-S'. See the 'h' for more help about less.
mysql> pager cat | tee /dr1/tmp/res.txt | tee /dr2/tmp/res2.txt | less -n -i -S
tee
enabled, pager set to 'less' and you will be able to browse the
results in unix 'less' and still have everything appended into a file the same
time. The difference between Unix tee used with the
pager and the mysql client in-built
tee, is that the in-built tee works even if you
don't have the Unix tee available. The in-built tee
also logs everything that is printed on the screen, where the Unix
tee used with pager doesn't log quite that much.
Last, but not least, the interactive tee is more handy to switch
on and off, when you want to log something into a file, but want to be able to
turn the feature off sometimes. A utility for performing administrative operations. The syntax is:
shell> mysqladmin [OPTIONS] command [command-option] command ...
You can get a list of the options your version of mysqladmin
supports by executing mysqladmin --help.
The current mysqladmin supports the following commands:
create databasename
drop databasename
extended-status
flush-hosts
flush-logs
flush-tables
flush-privileges
kill id,id,...
password
ping
processlist
reload
refresh
shutdown
slave-start
slave-stop
status
variables
version
All commands can be shortened to their unique prefix. For example:
shell> mysqladmin proc stat +----+-------+-----------+----+-------------+------+-------+------+ | Id | User | Host | db | Command | Time | State | Info | +----+-------+-----------+----+-------------+------+-------+------+ | 6 | monty | localhost | | Processlist | 0 | | | +----+-------+-----------+----+-------------+------+-------+------+ Uptime: 10077 Threads: 1 Questions: 9 Slow queries: 0 Opens: 6 Flush tables: 1 Open tables: 2 Memory in use: 1092K Max memory used: 1116K
The mysqladmin status command result has the
following columns:
| Column | Description |
| Uptime | Number of seconds the MySQL server has been up. |
| Threads | Number of active threads (clients). |
| Questions | Number of questions from clients since mysqld was
started. |
| Slow queries | Queries that have taken more than long_query_time
seconds. See section 4.9.5
The Slow Query Log. |
| Opens | How many tables mysqld has opened. |
| Flush tables | Number of flush ..., refresh, and
reload commands. |
| Open tables | Number of tables that are open now. |
| Memory in use | Memory allocated directly by the mysqld code (only
available when MySQL is compiled with --with-debug=full). |
| Max memory used | Maximum memory allocated directly by the mysqld code
(only available when MySQL is compiled with --with-debug=full). |
If you do myslqadmin shutdown on a socket (in other words, on a
the computer where mysqld is running), mysqladmin will
wait until the MySQL pid-file is removed to ensure that the
mysqld server has stopped properly.
mysqlcheck for Table Maintenance
and Crash RecoverySince MySQL version 3.23.38 you will be able to use a new checking and
repairing tool for MyISAM tables. The difference to
myisamchk is that mysqlcheck should be used when the
mysqld server is running, where as myisamchk should be
used when it is not. The benefit is that you no longer have to take the server
down for checking or repairing your tables.
mysqlcheck uses MySQL server commands CHECK,
REPAIR, ANALYZE and OPTIMIZE in a
convenient way for the user.
There are three alternative ways to invoke mysqlcheck:
shell> mysqlcheck [OPTIONS] database [tables] shell> mysqlcheck [OPTIONS] --databases DB1 [DB2 DB3...] shell> mysqlcheck [OPTIONS] --all-databases
So it can be used in a similar way as mysqldump when it comes to
what databases and tables you want to choose.
mysqlcheck does have a special feature compared to the other
clients; the default behavior, checking tables (-c), can be changed by renaming
the binary. So if you want to have a tool that repairs tables by default, you
should just copy mysqlcheck to your harddrive with a new name,
mysqlrepair, or alternatively make a symbolic link to
mysqlrepair and name the symbolic link as mysqlrepair.
If you invoke mysqlrepair now, it will repair tables by default.
The names that you can use to change mysqlcheck default behavior
are here:
mysqlrepair: The default option will be -r mysqlanalyze: The default option will be -a mysqloptimize: The default option will be -o
The options available for mysqlcheck are listed here, please
check what your version supports with mysqlcheck --help.
-A, --all-databases
-1, --all-in-1
-a, --analyze
--auto-repair
-#, --debug=...
--character-sets-dir=...
-c, --check
-C, --check-only-changed
--compress
-?, --help
-B, --databases
--default-character-set=...
-F, --fast
-f, --force
-e, --extended
-h, --host=...
-m, --medium-check
-o, --optimize
-p, --password[=...]
-P, --port=...
-q, --quick
-r, --repair
-s, --silent
-S, --socket=...
--tables
-u, --user=#
-v, --verbose
-V, --version
Utility to dump a database or a collection of database for backup or for transferring the data to another SQL server (not necessarily a MySQL server). The dump will contain SQL statements to create the table and/or populate the table.
If you are doing a backup on the server, you should consider using the
mysqlhotcopy instead. See section 4.8.6
mysqlhotcopy, Copying MySQL Databases and Tables.
shell> mysqldump [OPTIONS] database [tables] OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...] OR mysqldump [OPTIONS] --all-databases [OPTIONS]
If you don't give any tables or use the --databases or
--all-databases, the whole database(s) will be dumped.
You can get a list of the options your version of mysqldump
supports by executing mysqldump --help.
Note that if you run mysqldump without --quick or
--opt, mysqldump will load the whole result set into
memory before dumping the result. This will probably be a problem if you are
dumping a big database.
Note that if you are using a new copy of the mysqldump program
and you are going to do a dump that will be read into a very old MySQL server,
you should not use the --opt or -e options.
mysqldump supports the following options:
--add-locks
LOCK TABLES before and UNLOCK TABLE after
each table dump. (To get faster inserts into MySQL.)
--add-drop-table
drop table before each create statement.
-A, --all-databases
--databases with
all databases selected.
-a, --all
--allow-keywords
-c, --complete-insert
-C, --compress
-B, --databases
USE
db_name; will be included in the output before each new database.
--delayed
INSERT DELAYED command.
-e, --extended-insert
INSERT syntax. (Gives more compact and
faster inserts statements.)
-#, --debug[=option_string]
--help
--fields-terminated-by=...
--fields-enclosed-by=...
--fields-optionally-enclosed-by=...
--fields-escaped-by=...
--lines-terminated-by=...
-T option and have the same
meaning as the corresponding clauses for LOAD DATA INFILE. See
section 6.4.9
LOAD DATA INFILE Syntax.
-F, --flush-logs
-f, --force,
-h, --host=..
localhost.
-l, --lock-tables.
READ LOCAL to allow concurrent inserts in the case of
MyISAM tables.
-K, --no-disable-keys.
/*!40000 ALTER TABLE tb_name DISABLE KEYS */; and
/*!40000 ALTER TABLE tb_name ENABLE KEYS */; will not be put in
the output.
-n, --no-create-db
CREATE DATABASE /*!32312 IF NOT EXISTS*/ db_name; will not be
put in the output. The above line will be added otherwise, if --databases or
--all-databases option was given.
-t, --no-create-info
CREATE TABLE
statement).
-d, --no-data
--opt
--quick --add-drop-table --add-locks --extended-insert
--lock-tables. Should give you the fastest possible dump for reading
into a MySQL server.
-pyour_pass, --password[=your_pass]
mysqldump you will be prompted
for a password.
-P port_num, --port=port_num
localhost, for which Unix sockets
are used.)
-q, --quick
mysql_use_result() to do this.
-r, --result-file=...
-S /path/to/socket, --socket=/path/to/socket
localhost (which is
the default host).
--tables
-T, --tab=path-to-some-directory
table_name.sql file, that contains the SQL CREATE
commands, and a table_name.txt file, that contains the data, for
each give table. NOTE: This only works if
mysqldump is run on the same machine as the mysqld
daemon. The format of the .txt file is made according to the
--fields-xxx and --lines--xxx options.
-u user_name, --user=user_name
-O var=option, --set-variable var=option
-v, --verbose
-V, --version
-w, --where='where-condition'
-X, --xml
-x, --first-slave
"--where=user='jimf'" "-wuserid>1" "-wuserid<1"
-O net_buffer_length=#, where # < 16M
--extended-insert or --opt), mysqldump
will create rows up to net_buffer_length length. If you increase
this variable, you should also ensure that the max_allowed_packet
variable in the MySQL server is bigger than the
net_buffer_length. The most normal use of mysqldump is probably for making a backup
of whole databases. See section 4.4.1
Database Backups.
mysqldump --opt database > backup-file.sql
You can read this back into MySQL with:
mysql database < backup-file.sql
or
mysql -e "source /patch-to-backup/backup-file.sql" database
However, it's also very useful to populate another MySQL server with information from a database:
mysqldump --opt database | mysql --host=remote-host -C database
It is possible to dump several databases with one command:
mysqldump --databases database1 [database2 database3...] > my_databases.sql
If all the databases are wanted, one can use:
mysqldump --all-databases > all_databases.sql
mysqlhotcopy is a perl script that uses LOCK
TABLES, FLUSH TABLES and cp or scp
to quickly make a backup of a database. It's the fastest way to make a backup of
the database, of single tables but it can only be run on the same machine where
the database directories are.
mysqlhotcopy db_name [/path/to/new_directory] mysqlhotcopy db_name_1 ... db_name_n /path/to/new_directory mysqlhotcopy db_name./regex/
mysqlhotcopy supports the following options:
-?, --help
-u, --user=#
-p, --password=#
-P, --port=#
-S, --socket=#
--allowold
--keepold
--noindices
myisamchk
-rq..
--method=#
cp or scp).
-q, --quiet
--debug
-n, --dryrun
--regexp=#
--suffix=#
--checkpoint=#
--flushlog
--tmpdir=#
You can use perldoc mysqlhotcopy to get a more complete
documentation for mysqlhotcopy.
mysqlhotcopy reads the groups [client] and
[mysqlhotcopy] from the option files.
To be able to execute mysqlhotcopy you need write access to the
backup directory, SELECT privilege to the tables you are about to
copy and the MySQL Reload privilege (to be able to execute
FLUSH TABLES).
mysqlimport provides a command-line interface to the LOAD
DATA INFILE SQL statement. Most options to mysqlimport
correspond directly to the same options to LOAD DATA INFILE. See
section 6.4.9
LOAD DATA INFILE Syntax.
mysqlimport is invoked like this:
shell> mysqlimport [options] database textfile1 [textfile2....]
For each text file named on the command line, mysqlimport strips
any extension from the filename and uses the result to determine which table to
import the file's contents into. For example, files named
`patient.txt', `patient.text', and `patient' would
all be imported into a table named patient.
mysqlimport supports the following options:
-c, --columns=...
LOAD DATA INFILE
command, which is then passed to MySQL. See section 6.4.9
LOAD DATA INFILE Syntax.
-C, --compress
-#, --debug[=option_string]
-d, --delete
--fields-terminated-by=...
--fields-enclosed-by=...
--fields-optionally-enclosed-by=...
--fields-escaped-by=...
--lines-terminated-by=...
LOAD DATA INFILE. See section 6.4.9
LOAD DATA INFILE Syntax.
-f, --force
--force,
mysqlimport exits if a table doesn't exist.
--help
-h host_name, --host=host_name
localhost.
-i, --ignore
--replace option.
-l, --lock-tables
-L, --local
localhost (which is the default
host).
-pyour_pass, --password[=your_pass]
mysqlimport you will be prompted
for a password.
-P port_num, --port=port_num
localhost, for which Unix sockets
are used.)
-r, --replace
--replace and --ignore options control
handling of input records that duplicate existing records on unique key
values. If you specify --replace, new rows replace existing rows
that have the same unique key value. If you specify --ignore,
input rows that duplicate an existing row on a unique key value are skipped.
If you don't specify either option, an error occurs when a duplicate key value
is found, and the rest of the text file is ignored.
-s, --silent
-S /path/to/socket, --socket=/path/to/socket
localhost (which is
the default host).
-u user_name, --user=user_name
-v, --verbose
-V, --version
Here is a sample run using mysqlimport:
$ mysql --version mysql Ver 9.33 Distrib 3.22.25, for pc-linux-gnu (i686) $ uname -a Linux xxx.com 2.2.5-15 #1 Mon Apr 19 22:21:09 EDT 1999 i586 unknown $ mysql -e 'CREATE TABLE imptest(id INT, n VARCHAR(30))' test $ ed a 100 Max Sydow 101 Count Dracula . w imptest.txt 32 q $ od -c imptest.txt 0000000 1 0 0 \t M a x S y d o w \n 1 0 0000020 1 \t C o u n t D r a c u l a \n 0000040 $ mysqlimport --local test imptest.txt test.imptest: Records: 2 Deleted: 0 Skipped: 0 Warnings: 0 $ mysql -e 'SELECT * FROM imptest' test +------+---------------+ | id | n | +------+---------------+ | 100 | Max Sydow | | 101 | Count Dracula | +------+---------------+
mysqlshow can be used to quickly look at which databases exist,
their tables, and the table's columns.
With the mysql program you can get the same information with the
SHOW commands. See section 4.5.6
SHOW Syntax.
mysqlshow is invoked like this:
shell> mysqlshow [OPTIONS] [database [table [column]]]
Note that in newer MySQL versions, you only see those database/tables/columns for which you have some privileges.
If the last argument contains a shell or SQL wild-card (*,
?, % or _) then only what's matched by
the wild card is shown. This may cause some confusion when you try to display
the columns for a table with a _ as in this case
mysqlshow only shows you the table names that match the pattern.
This is easily fixed by adding an extra % last on the command line
(as a separate argument).
For most system errors MySQL will, in addition to a internal text message,
also print the system error code in one of the following styles: message
... (errno: #) or message ... (Errcode: #).
You can find out what the error code means by either examining the
documentation for your system or use the perror utility.
perror prints a description for a system error code, or an
MyISAM/ISAM table handler error code.
perror is invoked like this:
shell> perror [OPTIONS] [ERRORCODE [ERRORCODE...]] Example: shell> perror 13 64 Error code 13: Permission decided Error code 64: Machine is not on the network
Note that the error messages are mostly system dependent!
The mysql client typically is used interactively, like this:
shell> mysql database
However, it's also possible to put your SQL commands in a file and tell
mysql to read its input from that file. To do so, create a text
file `text_file' that contains the commands you wish to execute. Then
invoke mysql as shown below:
shell> mysql database < text_file
You can also start your text file with a USE db_name statement.
In this case, it is unnecessary to specify the database name on the command
line:
shell> mysql < text_file
See section 4.8 MySQL Client-Side Scripts and Utilities.
MySQL has several different log files that can help you find out what's going
on inside mysqld:
| Log file | Description |
| The error log | Problems encountering starting, running or stopping
mysqld. |
| The isam log | Logs all changes to the ISAM tables. Used only for debugging the isam code. |
| The query log | Established connections and executed queries. |
| The update log | Deprecated: Stores all statements that changes data |
| The binary log | Stores all statements that changes something. Used also for replication |
| The slow log | Stores all queries that took more than long_query_time to
execute or didn't use indexes. |
All logs can be found in the mysqld data directory. You can
force mysqld to reopen the log files (or in some cases switch to a
new log) by executing FLUSH LOGS. See section 4.5.3
FLUSH Syntax.
mysqld writes all errors to the stderr, which the
safe_mysqld script redirects to a file called
'hostname'.err. (On Windows, mysqld writes this
directly to `\mysql\data\mysql.err'.)
This contains information indicating when mysqld was started and
stopped and also any critical errors found when running. If mysqld
dies unexpectedly and safe_mysqld needs to restart
mysqld, safe_mysqld will write a restarted
mysqld row in this file. This log also holds a warning if
mysqld notices a table that needs to be automatically checked or
repaired.
On some operating systems, the error log will contain a stack trace for where
mysqld died. This can be used to find out where mysqld
died. See section E.1.4
Using a stack trace.
If you want to know what happens within mysqld, you should start
it with --log[=file]. This will log all connections and queries to
the log file (by default named `'hostname'.log'). This log can be very
useful when you suspect an error in a client and want to know exactly what
mysqld thought the client sent to it.
By default, the mysql.server script starts the MySQL server with
the -l option. If you need better performance when you start using
MySQL in a production environment, you can remove the -l option
from mysql.server or change it to --log-bin.
The entries in this log are written as mysqld receives the
questions. This may be different than the order in which the statements are
executed. This is in contrast to the update log and the binary log which are
written after the query is executed, but before any locks are released.
Note: The update log is replaced by the binary log. See section 4.9.4 The Binary Update Log. With this you can do anything that you can do with the update log.
When started with the --log-update[=file_name] option,
mysqld writes a log file containing all SQL commands that update
data. If no filename is given, it defaults to the name of the host machine. If a
filename is given, but it doesn't contain a path, the file is written in the
data directory. If `file_name' doesn't have an extension,
mysqld will create log file names like so:
`file_name.###', where ### is a number that is incremented
each time you execute mysqladmin refresh, execute mysqladmin
flush-logs, execute the FLUSH LOGS statement, or restart the
server.
Note: For the above scheme to work, you must not create your own files with the same filename as the update log + some extensions that may be regarded as a number, in the directory used by the update log!
If you use the --log or -l options,
mysqld writes a general log with a filename of
`hostname.log', and restarts and refreshes do not cause a new log file
to be generated (although it is closed and reopened). In this case you can copy
it (on Unix) by doing:
mv hostname.log hostname-old.log mysqladmin flush-logs cp hostname-old.log to-backup-directory rm hostname-old.log
Update logging is smart because it logs only statements that really update
data. So an UPDATE or a DELETE with a
WHERE that finds no rows is not written to the log. It even skips
UPDATE statements that set a column to the value it already has.
The update logging is done immediately after a query completes but before any locks are released or any commit is done. This ensures that the log will be logged in the execution order.
If you want to update a database from update log files, you could do the following (assuming your update logs have names of the form `file_name.###'):
shell> ls -1 -t -r file_name.[0-9]* | xargs cat | mysql
ls is used to get all the log files in the right order.
This can be useful if you have to revert to backup files after a crash and you want to redo the updates that occurred between the time of the backup and the crash.
The intention is that the binary log should replace the update log, so we recommend you to switch to this log format as soon as possible!
The binary log contains all information that is available in the update log in a more efficient format. It also contains information about how long every query that updated the database took.
The binary log is also used when you are replicating a slave from a master. See section 4.10 Replication in MySQL.
When started with the --log-bin[=file_name] option,
mysqld writes a log file containing all SQL commands that update
data. If no file name is given, it defaults to the name of the host machine
followed by -bin. If file name is given, but it doesn't contain a
path, the file is written in the data directory.
If you supply an extension to --log-bin=filename.extension, the
extension will be silenty removed.
To the binary log filename mysqld will append an extension that
is a number that is incremented each time you execute mysqladmin
refresh, execute mysqladmin flush-logs, execute the
FLUSH LOGS statement or restart the server. A new binary log will
also automaticly be created when it reaches max_bin_log_size. You
can delete all not active binary log files with the RESET MASTER
command. See section 4.5.4
RESET Syntax.
You can use the following options to mysqld to affect what is
logged to the binary log:
| Option | Description |
binlog-do-db=database_name |
Tells the master it should log updates for the specified database, and
exclude all others not explicitly mentioned. (Example:
binlog-do-db=some_database) |
binlog-ignore-db=database_name |
Tells the master that updates to the given database should not be
logged to the binary log (Example:
binlog-ignore-db=some_database) |
To be able to know which different binary log files have been used,
mysqld will also create a binary log index file that contains the
name of all used binary log files. By default this has the same name as the
binary log file, with the extension '.index'. You can change the
name of the binary log index file with the
--log-bin-index=[filename] option.
If you are using replication, you should not delete old binary log files
until you are sure that no slave will ever need to use them. One way to do this
is to do mysqladmin flush-logs once a day and then remove any logs
that are more than 3 days old.
You can examine the binary log file with the mysqlbinlog
command. For example, you can update a MySQL server from the binary log as
follows:
mysqlbinlog log-file | mysql -h server_name
You can also use the mysqlbinlog program to read the binary log
directly from a remote MySQL server!
mysqlbinlog --help will give you more information of how to use
this program!
If you are using BEGIN [WORK] or SET AUTOCOMMIT=0,
you must use the MySQL binary log for backups instead of the old update log.
The binary logging is done immediately after a query completes but before any locks are released or any commit is done. This ensures that the log will be logged in the execution order.
All updates (UPDATE, DELETE or INSERT)
that change a transactional table (like BDB tables) are cached until a
COMMIT. Any updates to a non-transactional table are stored in the
binary log at once. Every thread will, on start, allocate a buffer of
binlog_cache_size to buffer queries. If a query is bigger than
this, the thread will open a temporary file to handle the bigger cache. The
temporary file will be deleted when the thread ends.
The max_binlog_cache_size can be used to restrict the total size
used to cache a multi-transaction query.
If you are using the update or binary log, concurrent inserts will not work
together with CREATE ... INSERT and INSERT ... SELECT.
This is to ensure that you can recreate an exact copy of your tables by applying
the log on a backup.
When started with the --log-slow-queries[=file_name] option,
mysqld writes a log file containing all SQL commands that took more
than long_query_time to execute. The time to get the initial table
locks are not counted as execution time.
The slow query log is logged after the query is executed and after all locks has been released. This may be different than the order in which the statements are executed.
If no file name is given, it defaults to the name of the host machine
suffixed with -slow.log. If a filename is given, but doesn't
contain a path, the file is written in the data directory.
The slow query log can be used to find queries that take a long time to
execute and are thus candidates for optimisation. With a large log, that can
become a difficult task. You can pipe the slow query log through the
mysqldumpslow command to get a summary of the queries which appear
in the log.
You are using --log-long-format then also queries that are not
using indexes are printed. See section 4.1.1
mysqld Command-line Options.
MySQL has a lot of log files which make it easy to see what is going. See
section 4.9 The
MySQL Log Files. One must however from time to time clean up after
MysQL to ensure that the logs don't take up too much disk space.
When using MySQL with log files, you will, from time to time, want to remove/backup old log files and tell MySQL to start logging on new files. See section 4.4.1 Database Backups.
On a Linux (Redhat) installation, you can use the
mysql-log-rotate script for this. If you installed MySQL from an
RPM distribution, the script should have been installed automatically. Note that
you should be careful with this if you are using the log for replication!
On other systems you must install a short script yourself that you start from
cron to handle log files.
You can force MySQL to start using new log files by using mysqladmin
flush-logs or by using the SQL command FLUSH LOGS. If you
are using MySQL Version 3.21 you must use mysqladmin refresh.
The above command does the following:
--log) or slow query logging
(--log-slow-queries) is used, closes and reopens the log file
(`mysql.log' and ``hostname`-slow.log' as default).
--log-update) is used, closes the update
log and opens a new log file with a higher sequence number. If you are using only an update log, you only have to flush the logs and then move away the old update log files to a backup. If you are using the normal logging, you can do something like:
shell> cd mysql-data-directory shell> mv mysql.log mysql.old shell> mysqladmin flush-logs
and then take a backup and remove `mysql.old'.
This chapter describes the various replication features in MySQL. It serves as a reference to the options available with replication. You will be introduced to replication and learn how to implement it. Towards the end, there are some frequently asked questions and descriptions of problems and how to solve them.
We suggest that you visit our website at http://mysql.com/ often and read updates to this section. Replication is constantly being improved, and we update the manual frequently with the most current information.
One way replication can be used is to increase both robustness and speed. For robustness you can have two systems and can switch to the backup if you have problems with the master. The extra speed is achieved by sending a part of the non-updating queries to the replica server. Of course this only works if non-updating queries dominate, but that is the normal case.
Starting in Version 3.23.15, MySQL supports one-way replication internally. One server acts as the master, while the other acts as the slave. Note that one server could play the roles of master in one pair and slave in the other. The master server keeps a binary log of updates (see section 4.9.4 The Binary Update Log) and an index file to binary logs to keep track of log rotation. The slave, upon connecting, informs the master where it left off since the last successfully propagated update, catches up on the updates, and then blocks and waits for the master to notify it of the new updates.
Note that if you are replicating a database, all updates to this database should be done through the master!
Another benefit of using replication is that one can get live backups of the system by doing a backup on a slave instead of doing it on the master. See section 4.4.1 Database Backups.
MySQL replication is based on the server keeping track of all changes to your database (updates, deletes, etc) in the binary log (see section 4.9.4 The Binary Update Log) and the slave server(s) reading the saved queries from the master server's binary log so that the slave can execute the same queries on its copy of the data.
It is very important to realise that the binary log is simply a record starting from a fixed point in time (the moment you enable binary logging). Any slaves which you set up will need copies of all the data from your master as it existed the moment that you enabled binary logging on the master. If you start your slaves with data that doesn't agree with what was on the master when the binary log was started, your slaves may fail.
Starting in 4.0.0, one can use LOAD DATA FROM MASTER to set up a
slave. Note that 4.0.0 slaves cannot communicate with 3.23 masters, but 4.0.1
and later version slaves can. 3.23 slave cannot talk to 4.0 master.
You must also be aware that LOAD DATA FROM MASTER currently
works only if all the tables on the master are MyISAM type, and
will acuire a global read lock, so no writes are possible while the tables are
being transferred from the master. This limitation is of a temporary nature, and
is due to the fact that we have not yet implemented hot lock-free table backup.
It will be removed in the future 4.0 branch versions once we implemented hot
backup enabling LOAD DATA FROM MASTER to work without blocking
master updates.
Due to the above limitation, we recommend that at this point you use
LOAD DATA FROM MASTER only if the dataset on the master is
relatively small, or if a prolonged read lock on the master is acceptable. While
the actual speed of LOAD DATA FROM MASTER may vary from system to
system, a good rule for a rough estimate of how long it is going to take is 1
second per 1 MB of the data file. You will get close to the estimate if both
master and slave are equivalent to 700 MHz Pentium, are connected through 100
MBit/s network, and your index file is about half the size of your data file. Of
course, your mileage will vary from system to system, the above rule just gives
you a rough order of magnitude estimate.
Once a slave is properly configured and running, it will simply connect to
the master and wait for updates to process. If the master goes away or the slave
loses connectivity with your master, it will keep trying to connect every
master-connect-retry seconds until it is able to reconnect and
resume listening for updates.
Each slave keeps track of where it left off. The master server has no knowledge of how many slaves there are or which ones are up-to-date at any given time.
The next section explains the master/slave setup process in more detail.
Below is a quick description of how to set up complete replication on your current MySQL server. It assumes you want to replicate all your databases and have not configured replication before. You will need to shutdown your master server briefly to complete the steps outlined below.
While the above method is the most straightforward way to set up a slave, it is not the only one. For example, if you already have a snapshot of the master, and the master already has server id set and binary logging enabled, one can set up a slave without shutting the master down or even blocking the updates. Please refer to See section 4.10.7 Replication FAQ. for more details.
If you want to become a real MySQL replication guru, we suggest that you
begin with studing, pondering, and trying all commands mentioned in See section
4.10.6
SQL Commands Related to Replication. You should also familiarize yourself
with replication startup options in my.cnf in See section 4.10.5
Replication Options in my.cnf.
FILE
privilege and permission to connect from all the slaves. If the user is only
doing replication (which is recommended), you don't need to grant any
additional privileges. For example, to create a user named repl
which can access your master from any host, you might use this command: GRANT FILE ON *.* TO repl@"%" IDENTIFIED BY '<password>';
mysqladmin -u root -p<password> shutdown
tar -cvf /tmp/mysql-snapshot.tar /path/to/data-dirWindows users can use WinZip or similar software to create an archive of the data directory.
my.cnf on the master add log-bin and
server-id=unique number to the [mysqld] section and
restart it. It is very important that the id of the slave is different from
the id of the master. Think of server-id as something similar to
the IP address - it uniquely identifies the server instance in the community
of replication partners. [mysqld] log-bin server-id=1
my.cnf on the slave(s): master-host=<hostname of the master> master-user=<replication user name> master-password=<replication user password> master-port=<TCP/IP port for master> server-id=<some unique number between 2 and 2^32-1>replacing the values in <> with what is relevant to your system.
server-id must be different for each server participating in
replication. If you don't specify a server-id, it will be set to 1 if you have
not defined master-host, else it will be set to 2. Note that in
the case of server-id omission the master will refuse connections
from all slaves, and the slave will refuse to connect to a master. Thus,
omitting server-id is only good for backup with a binary log.
After you have done the above, the slave(s) should connect to the master and catch up on any updates which happened since the snapshot was taken.
If you have forgotten to set server-id for the slave you will
get the following error in the error log file:
Warning: one should set server_id to a non-0 value if master_host is set. The server will not act as a slave.
If you have forgot to do this for the master, the slaves will not be able to connect to the master.
If a slave is not able to replicate for any reason, you will find error messages in the error log on the slave.
Once a slave is replicating, you will find a file called
master.info in the same directory as your error log. The
master.info file is used by the slave to keep track of how much of
the master's binary log is has processed. Do not remove or edit
the file, unless you really know what you are doing. Even in that case, it is
preferred that you use CHANGE MASTER TO command.
Below is an explanation of what is supported and what is not:
AUTO_INCREMENT,
LAST_INSERT_ID, and TIMESTAMP values.
RAND() in updates does not replicate properly. Use
RAND(some_non_rand_expr) if you are replicating updates with
RAND(). You can, for example, use UNIX_TIMESTAMP()
for the argument to RAND().
--default-character-set) on the master and the slave. If not,
you may get duplicate key errors on the slave, because a key that is regarded
as unique on the master may not be that in the other character set.
LOAD DATA INFILE will be handled properly as long as
the file still resides on the master server at the time of update propagation.
LOAD LOCAL DATA INFILE will be skipped. In 4.0, this limitation
is not present - all forms of LOAD DATA INFILE are properly
replicated.
FLUSH commands are not stored in the binary log and are
because of this not replicated to the slaves. This is not normally a problem
as FLUSH doesn't change anything. This does however mean that if
you update the MySQL privilege tables directly without using
GRANT statement and you replicate the MySQL
privilege database, you must do a FLUSH PRIVILEGES on your slaves
to put the new privileges into effect.
SLAVE
STOP, then check Slave_open_temp_tables variable to see if
it is 0, then issue mysqladmin shutdown. If the number is not 0,
restart the slave thread with SLAVE START and see if you have
better luck next time. There will be a cleaner solution, but it has to wait
until version 4.0. In earlier versions temporary tables are not being
replicated properly - we recommend that you either upgrade, or execute
SET SQL_LOG_BIN=0 on your clients before all queries with temp
tables.
log-slave-updates enabled. Note,
however, that many queries will not work right in this kind of setup unless
your client code is written to take care of the potential problems that can
happen from updates that occur in different sequence on different servers.
This means that you can do a setup like the following: A -> B -> C -> AThis setup will only works if you only do non conflicting updates between the tables. In other words, if you insert data in A and C, you should never insert a row in A that may have a conflicting key with a row insert in C. You should also not update the sam rows on two servers if the order in which the updates are applied matters. Note that the log format has changed in Version 3.23.26 so that pre-3.23.26 slaves will not be able to read it.
.err file. You should then
connect to the slave manually, fix the cause of the error (for example,
non-existent table), and then run SLAVE START sql command
(available starting in Version 3.23.16). In Version 3.23.15, you will have to
restart the server.
master-connect-retry (default 60)
seconds. Because of this, it is safe to shut down the master, and then restart
it after a while. The slave will also be able to deal with network
connectivity outages.
master-port parameter in my.cnf .
replicate-do-db directives in my.cnf
or just exclude a set of databases with replicate-ignore-db. Note
that up until Version 3.23.23, there was a bug that did not properly deal with
LOAD DATA INFILE if you did it in a database that was excluded
from replication.
SET SQL_LOG_BIN = 0 will turn
off replication (binary) logging on the master, and SET SQL_LOG_BIN =
1 will turn in back on - you must have the process privilege to do
this.
FLUSH
MASTER and FLUSH SLAVE commands. In Version 3.23.26 we
have renamed them to RESET MASTER and RESET SLAVE
respectively to clarify what they do. The old FLUSH variants
still work, though, for compatibility.
LOAD TABLE FROM
MASTER for network backup and to set up replication initially. We have
recently received a number of bug reports concerning it that we are
investigating, so we recommend that you use it only in testing until we make
it more stable.
CHANGE MASTER TO.
binlog-ignore-db.
replicate-rewrite-db
to tell the slave to apply updates from one database on the master to the one
with a different name on the slave.
PURGE MASTER LOGS TO
'log-name' to get rid of old logs while the slave is running. If you are using replication, we recommend you to use MySQL Version 3.23.30 or later. Older versions work, but they do have some bugs and are missing some features. Some of the options below may not be available in your version if it is not the most recent one. For all options specific to the 4.0 branch, there is a note indicating so. Otherwise, if you discover that the option you are interested in is not available in your 3.23 version, and you really need it, please upgrade to the most recent 3.23 branch.
Please be aware that 4.0 branch is still in alpha, so some things may not be working as smoothly as you would like. If you really would like to try the new features of 4.0, we recommend you do it in such a way that in case there is a problem your mission critical applications will not be disrupted.
On both master and slave you need to use the server-id option.
This sets an unique replication id. You should pick a unique value in the range
between 1 to 2^32-1 for each master and slave. Example: server-id=3
The following table has the options you can use for the MASTER:
| Option | Description |
log-bin=filename |
Write to a binary update log to the specified location. Note that if
you give it a parameter with an extension (for example,
log-bin=/mysql/logs/replication.log ) versions up to 3.23.24
will not work right during replication if you do FLUSH LOGS .
The problem is fixed in Version 3.23.25. If you are using this kind of log
name, FLUSH LOGS will be ignored on binlog. To clear the log,
run FLUSH MASTER, and do not forget to run FLUSH
SLAVE on all slaves. In Version 3.23.26 and in later versions you
should use RESET MASTER and RESET SLAVE |
log-bin-index=filename |
Because the user could issue the FLUSH LOGS command, we
need to know which log is currently active and which ones have been
rotated out and in what sequence. This information is stored in the binary
log index file. The default is `hostname`.index. You can use this option
if you want to be a rebel. Example: log-bin-index=db.index.
|
sql-bin-update-same |
If set, setting SQL_LOG_BIN to a value will automatically
set SQL_LOG_UPDATE to the same value and vice versa. |
binlog-do-db=database_name |
Tells the master that it should log updates to the binary log if the
current database is 'database_name'. All others database are ignored. Note
that if you use this you should ensure that you only do updates in the
current database. Example: binlog-do-db=sales. |
binlog-ignore-db=database_name |
Tells the master that updates where the current database is
'database_name' should not be stored in the binary log. Note that if you
use this you should ensure that you only do updates in the current
database. Example: binlog-ignore-db=accounting
|
The following table has the options you can use for the SLAVE:
| Option | Description |
master-host=host |
Master hostname or IP address for replication. If not set, the slave
thread will not be started. Note that the setting of
master-host will be ignored if there exists a valid
master.info file. Probably a better name for this options
would have been something like bootstrap-master-host, but it
is too late to change now. Example:
master-host=db-master.mycompany.com. |
master-user=username |
The username the slave thread will use for authentication when
connecting to the master. The user must have FILE privilege.
If the master user is not set, user test is assumed. The
value in master.info will take precedence if it can be read.
Example: master-user=scott. |
master-password=password |
The password the slave thread will authenticate with when connecting
to the master. If not set, an empty password is assumed.The value in
master.info will take precedence if it can be read. Example:
master-password=tiger. |
master-port=portnumber |
The port the master is listening on. If not set, the compiled setting
of MYSQL_PORT is assumed. If you have not tinkered with
configure options, this should be 3306. The value in
master.info will take precedence if it can be read. Example:
master-port=3306. |
master-connect-retry=seconds |
The number of seconds the slave thread will sleep before retrying to
connect to the master in case the master goes down or the connection is
lost. Default is 60. Example: master-connect-retry=60. |
master-ssl |
Available after 4.0.0. Turn SSL on for replication. Be warned that is
this is a relatively new feature. Example: master-ssl. |
master-ssl-key |
Available after 4.0.0. Master SSL keyfile name. Only applies if you
have enabled master-ssl. Example:
master-ssl-key=SSL/master-key.pem. |
master-ssl-cert |
Available after 4.0.0. Master SSL certificate file name. Only applies
if you have enabled master-ssl. Example:
master-ssl-key=SSL/master-cert.pem. |
master-info-file=filename |
The location of the file that remembers where we left off on the
master during the replication process. The default is master.info in the
data directory. Sasha: The only reason I see for ever changing the default
is the desire to be rebelious. Example:
master-info-file=master.info. |
report-host |
Available after 4.0.0. Hostname or IP of the slave to be reported to
to the master during slave registration. Will appear in the output of
SHOW SLAVE HOSTS. Leave unset if you do not want the slave to
register itself with the master. Note that it is not sufficient for the
master to simply read the IP of the slave off the socket once the slave
connects. Due to NAT and other routing issues, that IP may
not be valid for connecting to the slave from the master or other hosts.
Example: report-host=slave1.mycompany.com |
report-port |
Available after 4.0.0. Port for connecting to slave reported to the master during slave registration. Set it only if the slave is listening on a non-default port or if you have a special tunnel from the master or other clients to the slave. If not sure, leave this option unset. |
replicate-do-table=db_name.table_name |
Tells the slave thread to restrict replication to the specified table.
To specify more than one table, use the directive multiple times, once for
each table. This will work for cross-database updates, in contrast to
replicate-do-db. Example:
replicate-do-table=some_db.some_table. |
replicate-ignore-table=db_name.table_name |
Tells the slave thread to not replicate to the specified table. To
specify more than one table to ignore, use the directive multiple times,
once for each table. This will work for cross-datbase updates, in contrast
to replicate-ignore-db. Example:
replicate-ignore-table=db_name.some_table. |
replicate-wild-do-table=db_name.table_name |
Tells the slave thread to restrict replication to the tables that
match the specified wildcard pattern. To specify more than one table, use
the directive multiple times, once for each table. This will work for
cross-database updates. Example:
replicate-wild-do-table=foo%.bar% will replicate only updates
to tables in all databases that start with foo and whose table names start
with bar. |
replicate-wild-ignore-table=db_name.table_name |
Tells the slave thread to not replicate to the tables that match the
given wild card pattern. To specify more than one table to ignore, use the
directive multiple times, once for each table. This will work for
cross-database updates. Example:
replicate-wild-ignore-table=foo%.bar% will not do updates to
tables in databases that start with foo and whose table names start with
bar. |
replicate-ignore-db=database_name |
Tells the slave thread to not replicate to the specified database. To
specify more than one database to ignore, use the directive multiple
times, once for each database. This option will not work if you use cross
database updates. If you need cross database updates to work, make sure
you have 3.23.28 or later, and use
replicate-wild-ignore-table=db_name.% Example:
replicate-ignore-db=some_db. |
replicate-do-db=database_name |
Tells the slave thread to restrict replication to the specified
database. To specify more than one database, use the directive multiple
times, once for each database. Note that this will only work if you do not
use cross-database queries such as UPDATE some_db.some_table SET
foo='bar' while having selected a different or no database. If you
need cross database updates to work, make sure you have 3.23.28 or later,
and use replicate-wild-do-table=db_name.% Example:
replicate-do-db=some_db. |
log-slave-updates |
Tells the slave to log the updates from the slave thread to the binary log. Off by default. You will need to turn it on if you plan to daisy-chain the slaves. |
replicate-rewrite-db=from_name->to_name |
Updates to a database with a different name than the original Example:
replicate-rewrite-db=master_db_name->slave_db_name. |
slave-skip-errors=err_code1,err_code2,.. |
Available only in 3.23.47 and later. Tells the slave thread to
continue replication when a query returns an error from the provided list.
Normally, replication will discontinue when an error is encountered giving
the user a chance to resolve the inconsistency in the data manually. Do
not use this option unless you fully understand why you are getting the
errors. If there are no bugs in your replication setup and client
programs, and no bugs in MySQL itself, you should never get an abort with
error.Indiscriminate use of this option will result in slaves being
hopelessly out of sync with the master and you having no idea how the
problem happened. For error codes, you should use the numbers provided by
the error message in your slave error log and in the output of SHOW
SLAVE STATUS. Full list of error messages can be found in the
source distribution in Docs/mysqld_error.txt. You can ( but
should not) also use a very non-recommended value of all
which will ignore all error messages and keep barging along regardless.
Needless to say, if you use it, we make no promises regarding your data
integrity. Please do not complain if your data on the slave is not
anywhere close to what it is on the master in this case - you have been
warned. Example: slave-skip-errors=1062,1053 or
slave-skip-errors=all |
skip-slave-start |
Tells the slave server not to start the slave on the startup. The user
can start it later with SLAVE START. |
slave_read_timeout=# |
Number of seconds to wait for more data from the master before aborting the read. |
Replication can be controlled through the SQL interface. Below is the summary of commands:
| Command | Description |
SLAVE START |
Starts the slave thread. (Slave) |
SLAVE STOP |
Stops the slave thread. (Slave) |
SET SQL_LOG_BIN=0 |
Disables update logging if the user has process privilege. Ignored otherwise. (Master) |
SET SQL_LOG_BIN=1 |
Re-enables update logging if the user has process privilege. Ignored otherwise. (Master) |
SET SQL_SLAVE_SKIP_COUNTER=n |
Skip the next n events from the master. Only valid when
the slave thread is not running, otherwise, gives an error. Useful for
recovering from replication glitches. |
RESET MASTER |
Deletes all binary logs listed in the index file, resetting the binlog
index file to be empty. In pre-3.23.26 versions, FLUSH MASTER
(Master) |
RESET SLAVE |
Makes the slave forget its replication position in the master logs. In
pre 3.23.26 versions the command was called FLUSH
SLAVE(Slave) |
LOAD TABLE tblname FROM MASTER |
Downloads a copy of the table from master to the slave. Implemented
mainly for debugging of LOAD DATA FROM MASTER, but some
"gourmet" users might find it useful for other things. Do not use it if
you consider yourself the average "non-hacker" type user. (Slave) |
LOAD DATA FROM MASTER |
Available starting in 4.0.0. Takes a snapshot of the master and copies
it to the slave. Updates the values of MASTER_LOG_FILE and
MASTER_LOG_POS so that the slave will start replicating from
the correct position. Will honor table and database exclusion rules
specified with replicate-* options. So far works only with
MyISAM tables and acquires a global read lock on the master
while taking the snapshot. In the future it is planned to make it work
with InnoDB tables and to remove the need for global read
lock using the non-blocking online backup feature. |
CHANGE MASTER TO master_def_list |
Changes the master parameters to the values specified in
master_def_list and restarts the slave thread.
master_def_list is a comma-separated list of
master_def where master_def is one of the
following: MASTER_HOST, MASTER_USER,
MASTER_PASSWORD, MASTER_PORT,
MASTER_CONNECT_RETRY, MASTER_LOG_FILE,
MASTER_LOG_POS. For example: CHANGE MASTER TO MASTER_HOST='master2.mycompany.com', MASTER_USER='replication', MASTER_PASSWORD='bigs3cret', MASTER_PORT=3306, MASTER_LOG_FILE='master2-bin.001', MASTER_LOG_POS=4;You only need to specify the values that need to be changed. The values that you omit will stay the same with the exception of when you change the host or the port. In that case, the slave will assume that since you are connecting to a different host or a different port, the master is different. Therefore, the old values of log and position are not applicable anymore, and will automatically be reset to an empty string and 0, respectively (the start values). Note that if you restart the slave, it will remember its last master. If this is not desirable, you should delete the `master.info' file before restarting, and the slave will read its master from my.cnf or the command line. This command is
useful for setting up a slave when you have the snapshot of the master and
have record the log and the offset on the master that the snapshot
corresponds to. You can run CHANGE MASTER TO
MASTER_LOG_FILE='log_name_on_master',
MASTER_LOG_POS=log_offset_on_master on the slave after restoring
the snapshot. (Slave) |
SHOW MASTER STATUS |
Provides status information on the binlog of the master. (Master) |
SHOW SLAVE HOSTS |
Available after 4.0.0. Gives a listing of slaves currently registered with the master (Master) |
SHOW SLAVE STATUS |
Provides status information on essential parameters of the slave thread. (Slave) |
SHOW MASTER LOGS |
Only available starting in Version 3.23.28. Lists the binary logs on
the master. You should use this command prior to PURGE MASTER LOGS
TO to find out how far you should go. (Master) |
SHOW BINLOG EVENTS [ IN 'logname' ] [ FROM pos ] [ LIMIT
[offset,] rows ] |
Shows the events in the binary update log. Primarily used for testing/debugging, but can also be used by regular clients that for some reason need to read the binary log contents. (Master) |
SHOW NEW MASTER FOR SLAVE WITH MASTER_LOG_FILE='logfile' AND
MASTER_LOG_POS=pos AND MASTER_LOG_SEQ=log_seq AND
MASTER_SERVER_ID=server_id |
This command is used when a slave of a possibly dead/unavailable
master needs to be switched to replicate off another slave that has been
replicating the same master. The command will return recalculated
replication coordinates, and the output can be used in a subsequent
CHANGE MASTER TO command. Normal users should never need to
run this command. It is primarily reserved for internal use by the
fail-safe replication code. We may later change the syntax if we find a
more intuitive way to describe this operation. |
PURGE MASTER LOGS TO 'logname' |
Available starting in Version 3.23.28. Deletes all the replication
logs that are listed in the log index as being prior to the specified log,
and removed them from the log index, so that the given log now becomes
first. Example: PURGE MASTER LOGS TO 'mysql-bin.010'This command will do nothing and fail with an error if you have an active slave that is currently reading one of the logs you are trying to delete. However, if you have a dormant slave, and happen to purge one of the logs it wants to read, the slave will be unable to replicate once it comes up. The command is safe to run while slaves are replicating - you do not need to stop them. You must first check all the slaves with SHOW
SLAVE STATUS to see which log they are on, then do a listing of the
logs on the master with SHOW MASTER LOGS, find the earliest
log among all the slaves (if all the slaves are up to date, this will be
the last log on the list), backup all the logs you are about to delete
(optional) and purge up to the target log. |
Q: How do I configure a slave if the master is already running and I do not want to stop it?
A: There are several options. If you have taken a backup of
the master at some point and recorded the binlog name and offset ( from the
output of SHOW MASTER STATUS ) corresponding to the snapshot, do
the following:
CHANGE MASTER TO MASTER_HOST='master-host-name',
MASTER_USER='master-user-name', MASTER_PASSWORD='master-pass',
MASTER_LOG_FILE='recorded-log-name', MASTER_LOG_POS=recorded_log_pos
SLAVE START If you do not have a backup of the master already, here is a quick way to do it consistently:
FLUSH TABLES WITH READ LOCK
gtar zcf /tmp/backup.tar.gz /var/lib/mysql ( or a variation
of this)
SHOW MASTER STATUS - make sure to record the output - you
will need it later
UNLOCK TABLES Afterwards, follow the instructions for the case when you have a snapshot and have records the log name and offset. You can use the same snapshot to set up several slaves. As long as the binary logs of the master are left intact, you can wait as long as several days or in some cases maybe a month to set up a slave once you have the snapshot of the master. In theory the waiting gap can be infinite. The two practical limitations is the diskspace of the master getting filled with old logs, and the amount of time it will take the slave to catch up.
In version 4.0.0 and newer, you can also use LOAD DATA FROM
MASTER. This is a convenient command that will take a snapshot, restore
it to the slave, and adjust the log name and offset on the slave all at once. In
the future, LOAD DATA FROM MASTER will be the recommended way to
set up a slave. Be warned, howerver, that the read lock may be held for a long
time if you use this command. It is not yet implemented as efficiently as we
would like to have it. If you have large tables, the preferred method at this
time is still with a local tar snapshot after executing FLUSH
TABLES WITH READ LOCK.
Q: Does the slave need to be connected to the master all the time?
A: No, it does not. You can have the slave go down or stay disconnected for hours or even days, then reconnect, catch up on the updates, and then disconnect or go down for a while again. So you can, for example, use master-slave setup over a dial-up link that is up only for short periods of time. The implications of that are that at any given time the slave is not guaranteed to be in sync with the master unless you take some special measures. In the future, we will have the option to block the master until at least one slave is in sync.
Q: How do I force the master to block updates until the slave catches up?
A: Execute the following commands:
FLUSH TABLES WITH READ LOCK
SHOW MASTER STATUS - record the log name and the
offset
SELECT MASTER_POS_WAIT('recorded_log_name',
recorded_log_offset) When the select returns, the slave is currently in
sync with the master
UNLOCK TABLES - now the master will continue updates.
Q: Why do I sometimes see more than one
Binlog_Dump thread on the master after I have restarted the slave?
A: Binlog_Dump is a continuous process that is
handled by the server in the following way:
pthread_cond_wait(), from which we can be awakened either by an
update or a kill.
Binlog_dump loop.
So if the slave thread stops on the slave, the corresponding
Binlog_Dump thread on the master will not notice it until after at
least one update to the master (or a kill), which is needed to wake it up from
pthread_cond_wait(). In the meantime, the slave could have opened
another connection, which resulted in another Binlog_Dump thread.
The above problem should not be present in Version 3.23.26 and later
versions. In Version 3.23.26 we added server-id to each replication
server, and now all the old zombie threads are killed on the master when a new
replication thread connects from the same slave
Q: How do I rotate replication logs?
A: In Version 3.23.28 you should use PURGE MASTER LOGS
TO command after determining which logs can be deleted, and optionally
backing them up first. In earlier versions the process is much more painful, and
cannot be safely done without stopping all the slaves in the case that you plan
to re-use log names. You will need to stop the slave threads, edit the binary
log index file, delete all the old logs, restart the master, start slave
threads, and then remove the old log files.
Q: How do I upgrade on a hot replication setup?
A: If you are upgrading pre-3.23.26 versions, you should
just lock the master tables, let the slave catch up, then run FLUSH
MASTER on the master, and FLUSH SLAVE on the slave to reset
the logs, then restart new versions of the master and the slave. Note that the
slave can stay down for some time - since the master is logging all the updates,
the slave will be able to catch up once it is up and can connect.
After 3.23.26, we have locked the replication protocol for modifications, so you can upgrade masters and slave on the fly to a newer 3.23 version and you can have different versions of MySQL running on the slave and the master, as long as they are both newer than 3.23.26.
Q: What issues should I be aware of when setting up two-way replication?
A: MySQL replication currently does not support any locking protocol between master and slave to guarantee the atomicity of a distributed (cross-server) update. In in other words, it is possible for client A to make an update to co-master 1, and in the meantime, before it propagates to co-master 2, client B could make an update to co-master 2 that will make the update of client A work differently than it did on co-master 1. Thus when the update of client A will make it to co-master 2, it will produce tables that will be different than what you have on co-master 1, even after all the updates from co-master 2 have also propagated. So you should not co-chain two servers in a two-way replication relationship, unless you are sure that you updates can safely happen in any order, or unless you take care of mis-ordered updates somehow in the client code.
You must also realise that two-way replication actually does not improve performance very much, if at all, as far as updates are concerned. Both servers need to do the same amount of updates each, as you would have one server do. The only difference is that there will be a little less lock contention, because the updates originating on another server will be serialised in one slave thread. This benefit, though, might be offset by network delays.
Q: How can I use replication to improve performance of my system?
A: You should set up one server as the master, and direct
all writes to it, and configure as many slaves as you have the money and
rackspace for, distributing the reads among the master and the slaves. You can
also start the slaves with --skip-bdb,
--low-priority-updates and
--delay-key-write-for-all-tables to get speed improvements for the
slave. In this case the slave will use non-transactional MyISAM
tables instead of BDB tables to get more speed.
Q: What should I do to prepare my client code to use performance-enhancing replication?
A: If the part of your code that is responsible for database access has been properly abstracted/modularised, converting it to run with the replicated setup should be very smooth and easy - just change the implementation of your database access to read from some slave or the master, and to always write to the master. If your code does not have this level of abstraction, setting up a replicated system will give you an opportunity/motivation to it clean up. You should start by creating a wrapper library /module with the following functions:
safe_writer_connect()
safe_reader_connect()
safe_reader_query()
safe_writer_query() safe_ means that the function will take care of handling all the
error conditions.
You should then convert your client code to use the wrapper library. It may
be a painful and scary process at first, but it will pay off in the long run.
All applications that follow the above pattern will be able to take advantage of
one-master/many slaves solution. The code will be a lot easier to maintain, and
adding troubleshooting options will be trivial. You will just need to modify one
or two functions, for example, to log how long each query took, or which query,
among your many thousands, gave you an error. If you have written a lot of code
already, you may want to automate the conversion task by using Monty's
replace utility, which comes with the standard distribution of
MySQL, or just write your own Perl script. Hopefully, your code follows some
recognisable pattern. If not, then you are probably better off re-writing it
anyway, or at least going through and manually beating it into a pattern.
Note that, of course, you can use different names for the functions. What is important is having unified interface for connecting for reads, connecting for writes, doing a read, and doing a write.
Q: When and how much can MySQL replication improve the performance of my system?
A: MySQL replication is most beneficial for a system with frequent reads and not so frequent writes. In theory, by using a one master/many slaves setup you can scale by adding more slaves until you either run out of network bandwidth, or your update load grows to the point that the master cannot handle it.
In order to determine how many slaves you can get before the added benefits
begin to level out, and how much you can improve performance of your site, you
need to know your query patterns, and empirically (by benchmarking) determine
the relationship between the throughput on reads (reads per second, or
max_reads) and on writes max_writes) on a typical
master and a typical slave. The example below will show you a rather simplified
calculation of what you can get with replication for our imagined system.
Let's say our system load consists of 10% writes and 90% reads, and we have
determined that max_reads = 1200 - 2 * max_writes, or
in other words, our system can do 1200 reads per second with no writes, our
average write is twice as slow as average read, and the relationship is linear.
Let us suppose that our master and slave are of the same capacity, and we have N
slaves and 1 master. Then we have for each server (master or slave):
reads = 1200 - 2 * writes (from bencmarks)
reads = 9* writes / (N + 1) (reads split, but writes go to all
servers)
9*writes/(N+1) + 2 * writes = 1200
writes = 1200/(2 + 9/(N+1)
So if N = 0, which means we have no replication, our system can handle 1200/11, about 109 writes per second (which means we will have 9 times as many reads due to the nature of our application).
If N = 1, we can get up to 184 writes per second.
If N = 8, we get up to 400.
If N = 17, 480 writes.
Eventually as N approaches infinity (and our budget negative infinity), we can get very close to 600 writes per second, increasing system throughput about 5.5 times. However, with only 8 servers, we increased it almost 4 times already.
Note that our computations assumed infinite network bandwidth, and neglected several other factors that could turn out to be significant on your system. In many cases, you may not be able to make a computation similar to the one above that will accurately predict what will happen on your system if you add N replication slaves. However, answering the following questions should help you decided whether and how much, if at all, the replication will improve the performance of your system:
Q: How can I use replication to provide redundancy/high availability?
A: With the currently available features, you would have to set up a master and a slave (or several slaves), and write a script that will monitor the master to see if it is up, and instruct your applications and the slaves of the master change in case of failure. Some suggestions:
CHANGE MASTER TO
command.
nsupdate to dynamically update your DNS.
log-bin option and
without log-slave-updates. This way the slave will be ready to
become a master as soon as you issue STOP SLAVE; RESET
MASTER, and CHANGE MASTER TO on the other slaves. It will
also help you catch spurious updates that may happen because of
misconfiguration of the slave (ideally, you want to configure access rights so
that no client can update the slave, except for the slave thread) combined
with the bugs in your client programs (they should never update the slave
directly). We are currently working on integrating an automatic master election system into MySQL, but until it is ready, you will have to create your own monitoring tools.
If you have followed the instructions, and your replication setup is not working, first eliminate the user error factor by checking the following:
SHOW MASTER
STATUS. If it is, Position will be non-zero. If not,
verify that you have given the master log-bin option and have set
server-id.
SHOW SLAVE STATUS. The
answer is found in Slave_running column. If not, verify slave
options and check the error log for messages.
SHOW PROCESSLIST, find the thread with system user
value in User column and none in the
Host column, and check the State column. If it says
connecting to master, verify the privileges for the replication
user on the master, master host name, your DNS setup, whether the master is
actually running, whether it is reachable from the slave, and if all that
seems okay, read the error logs.
SLAVE START
SET
SQL_SLAVE_SKIP_COUNTER=1; SLAVE START; to skip a query that does not
use auto_increment, or last_insert_id or SET SQL_SLAVE_SKIP_COUNTER=2;
SLAVE START; otherwise. The reason auto_increment/last_insert_id
queries are different is that they take two events in the binary log of the
master.
grep -i
slave /path/to/your-log.err on the slave. There is no generic pattern
to search for on the master, as the only errors it logs are general system
errors - if it can, it will send the error to the slave when things go wrong.
When you have determined that there is no user error involved, and
replication still either does not work at all or is unstable, it is time to
start working on a bug report. We need to get as much info as possible from you
to be able to track down the bug. Please do spend some time and effort preparing
a good bug report. Ideally, we would like to have a test case in the format
found in mysql-test/t/rpl* directory of the source tree. If you
submit a test case like that, you can expect a patch within a day or two in most
cases, although, of course, you mileage may vary depending on a number of
factors.
Second best option is a just program with easily configurable connection arguments for the master and the slave that will demonstrate the problem on our systems. You can write one in Perl or in C, depending on which language you know better.
If you have one of the above ways to demonstrate the bug, use
mysqlbug to prepare a bug report and send it to bugs@lists.mysql.com. If you have a
phantom - a problem that does occur but you cannot duplicate "at will":
log-slave-updates and log-bin -
this will keep a log of all updates on the slave.
SHOW MASTER STATUS on the master at the time
you have discovered the problem
SHOW SLAVE STATUS on the master at the time
you have discovered the problem
mysqlbinlog to examine the binary logs. The following
should be helpful to find the trouble query, for example: mysqlbinlog -j pos_from_slave_status /path/to/log_from_slave_status | head
Once you have collected the evidence on the phantom problem, try hard to isolate it into a separate test case first. Then report the problem to bugs@lists.mysql.com with as much info as possible.
Optimisation is a complicated task because it ultimately requires understanding of the whole system. While it may be possible to do some local optimisations with small knowledge of your system or application, the more optimal you want your system to become the more you will have to know about it.
This chapter will try to explain and give some examples of different ways to optimise MySQL. Remember, however, that there are always some (increasingly harder) additional ways to make the system even faster.
The most important part for getting a system fast is of course the basic design. You also need to know what kinds of things your system will be doing, and what your bottlenecks are.
The most common bottlenecks are:
When using the MyISAM table handler, MySQL uses extremely fast table locking (multiple readers / single writers). The biggest problem with this table type is a if you have a mix of a steady stream of updates and slow selects on the same table. If this is a problem with some tables, you can use another table type for these. See section 7 MySQL Table Types.
MySQL can work with both transactional and not transactional tables. To be able to work smoothly with not transactional tables (which can't rollback if something goes wrong), MySQL has the following rules:
NULL in a
NOT NULL column or a too big numerical value in a numerical
column, MySQL will instead of giving an error instead set the column to the
'best possible value'. For numerical values this is 0, the smallest possible
values or the largest possible value. For strings this is either the empty
string or the longest possible string that can be in the column.
NULL
The reason for the above rules is that we can't check these conditions before the query starts to execute. If we encounter a problem after updating a few rows, we can't just rollback as the table type may not support this. We can't stop because in that case the update would be 'half done' which is probably the worst possible scenario. In this case it's better to 'do the best you can' and then continue as if nothing happened.
The above means that one should not use MySQL to check fields content, but one should do this in the application.
Because all SQL servers implement different parts of SQL, it takes work to write portable SQL applications. For very simple selects/inserts it is very easy, but the more you need the harder it gets. If you want an application that is fast with many databases it becomes even harder!
To make a complex application portable you need to choose a number of SQL servers that it should work with.
You can use the MySQL crash-me program/web-page http://www.mysql.com/information/crash-me.php to find functions, types, and limits you can use with a selection of database servers. Crash-me now tests far from everything possible, but it is still comprehensive with about 450 things tested.
For example, you shouldn't have column names longer than 18 characters if you want to be able to use Informix or DB2.
Both the MySQL benchmarks and crash-me programs are very database-independent. By taking a look at how we have handled this, you can get a feeling for what you have to do to write your application database-independent. The benchmarks themselves can be found in the `sql-bench' directory in the MySQL source distribution. They are written in Perl with DBI database interface (which solves the access part of the problem).
See http://mysql.com/information/benchmarks.html for the results from this benchmark.
As you can see in these results, all databases have some weak points. That is, they have different design compromises that lead to different behavior.
If you strive for database independence, you need to get a good feeling for each SQL server's bottlenecks. MySQL is very fast in retrieving and updating things, but will have a problem in mixing slow readers/writers on the same table. Oracle, on the other hand, has a big problem when you try to access rows that you have recently updated (until they are flushed to disk). Transaction databases in general are not very good at generating summary tables from log tables, as in this case row locking is almost useless.
To get your application really database-independent, you need to define an easy extendable interface through which you manipulate your data. As C++ is available on most systems, it makes sense to use a C++ classes interface to the databases.
If you use some specific feature for some database (like the
REPLACE command in MySQL), you should code a method for the other
SQL servers to implement the same feature (but slower). With MySQL you can use
the /*! */ syntax to add MySQL-specific keywords to a query. The
code inside /**/ will be treated as a comment (ignored) by most
other SQL servers.
If high performance is more important than exactness, as in some Web applications, it is possibile to create an application layer that caches all results to give you even higher performance. By letting old results 'expire' after a while, you can keep the cache reasonably fresh. This provides a method to handle high load spikes, in which case you can dynamically increase the cache and set the expire timeout higher until things get back to normal.
In this case the table creation information should contain information of the initial size of the cache and how often the table should normally be refreshed.
During MySQL initial development, the features of MySQL were made to fit our largest customer. They handle data warehousing for a couple of the biggest retailers in Sweden.
From all stores, we get weekly summaries of all bonus card transactions, and we are expected to provide useful information for the store owners to help them find how their advertisement campaigns are affecting their customers.
The data is quite huge (about 7 million summary transactions per month), and we have data for 4-10 years that we need to present to the users. We got weekly requests from the customers that they want to get 'instant' access to new reports from this data.
We solved this by storing all information per month in compressed 'transaction' tables. We have a set of simple macros (script) that generates summary tables grouped by different criteria (product group, customer id, store ...) from the transaction tables. The reports are Web pages that are dynamically generated by a small Perl script that parses a Web page, executes the SQL statements in it, and inserts the results. We would have used PHP or mod_perl instead but they were not available at that time.
For graphical data we wrote a simple tool in C that can produce
GIFs based on the result of a SQL query (with some processing of the result).
This is also dynamically executed from the Perl script that parses the
HTML files.
In most cases a new report can simply be done by copying an existing script and modifying the SQL query in it. In some cases, we will need to add more fields to an existing summary table or generate a new one, but this is also quite simple, as we keep all transactions tables on disk. (Currently we have at least 50G of transactions tables and 200G of other customer data.)
We also let our customers access the summary tables directly with ODBC so that the advanced users can themselves experiment with the data.
We haven't had any problems handling this with quite modest Sun Ultra SPARCstation (2x200 Mhz). We recently upgraded one of our servers to a 2 CPU 400 Mhz UltraSPARC, and we are now planning to start handling transactions on the product level, which would mean a ten-fold increase of data. We think we can keep up with this by just adding more disk to our systems.
We are also experimenting with Intel-Linux to be able to get more CPU power cheaper. Now that we have the binary portable database format (new in Version 3.23), we will start to use this for some parts of the application.
Our initial feelings are that Linux will perform much better on low-to-medium load and Solaris will perform better when you start to get a high load because of extreme disk IO, but we don't yet have anything conclusive about this. After some discussion with a Linux Kernel developer, this might be a side effect of Linux giving so much resources to the batch job that the interactive performance gets very low. This makes the machine feel very slow and unresponsive while big batches are going. Hopefully this will be better handled in future Linux Kernels.
This should contain a technical description of the MySQL benchmark suite (and
crash-me), but that description is not written yet. Currently, you
can get a good idea of the benchmark by looking at the code and results in the
`sql-bench' directory in any MySQL source distributions.
This benchmark suite is meant to be a benchmark that will tell any user what things a given SQL implementation performs well or poorly at.
Note that this benchmark is single threaded, so it measures the minimum time for the operations. We plan to in the future add a lot of multi-threaded tests to the benchmark suite.
For example, (run on the same NT 4.0 machine):
| Reading 2000000 rows by index | Seconds | Seconds |
| mysql | 367 | 249 |
| mysql_odbc | 464 | |
| db2_odbc | 1206 | |
| informix_odbc | 121126 | |
| ms-sql_odbc | 1634 | |
| oracle_odbc | 20800 | |
| solid_odbc | 877 | |
| sybase_odbc | 17614 |
| Inserting (350768) rows | Seconds | Seconds |
| mysql | 381 | 206 |
| mysql_odbc | 619 | |
| db2_odbc | 3460 | |
| informix_odbc | 2692 | |
| ms-sql_odbc | 4012 | |
| oracle_odbc | 11291 | |
| solid_odbc | 1801 | |
| sybase_odbc | 4802 |
In the above test MySQL was run with a 8M index cache.
We have gather some more benchmark results at http://mysql.com/information/benchmarks.html.
Note that Oracle is not included because they asked to be removed. All Oracle benchmarks have to be passed by Oracle! We believe that makes Oracle benchmarks very biased because the above benchmarks are supposed to show what a standard installation can do for a single client.
To run the benchmark suite, you have to download a MySQL source distribution, install the perl DBI driver, the perl DBD driver for the database you want to test and then do:
cd sql-bench perl run-all-tests --server=#
where # is one of supported servers. You can get a list of all options and
supported servers by doing run-all-tests --help.
crash-me tries to determine what features a
database supports and what its capabilities and limitations are by actually
running queries. For example, it determines:
VARCHAR column can be We can find the result from crash-me on a lot of different databases at http://www.mysql.com/information/crash-me.php.
You should definitely benchmark your application and database to find out where the bottlenecks are. By fixing it (or by replacing the bottleneck with a 'dummy module') you can then easily identify the next bottleneck (and so on). Even if the overall performance for your application is sufficient, you should at least make a plan for each bottleneck, and decide how to solve it if someday you really need the extra performance.
For an example of portable benchmark programs, look at the MySQL benchmark suite. See section 5.1.4 The MySQL Benchmark Suite. You can take any program from this suite and modify it for your needs. By doing this, you can try different solutions to your problem and test which is really the fastest solution for you.
It is very common that some problems only occur when the system is very heavily loaded. We have had many customers who contact us when they have a (tested) system in production and have encountered load problems. In every one of these cases so far, it has been problems with basic design (table scans are not good at high load) or OS/Library issues. Most of this would be a lot easier to fix if the systems were not already in production.
To avoid problems like this, you should put some effort into benchmarking your whole application under the worst possible load! You can use Super Smack for this, and it is available at: http://mysql.com/Downloads/super-smack/super-smack-1.0.tar.gz. As the name suggests, it can bring your system down to its knees if you ask it, so make sure to use it only on your development systems.
SELECTs and Other QueriesFirst, one thing that affects all queries: The more complex permission system setup you have, the more overhead you get.
If you do not have any GRANT statements done, MySQL will
optimise the permission checking somewhat. So if you have a very high volume it
may be worth the time to avoid grants. Otherwise more permission check results
in a larger overhead.
If your problem is with some explicit MySQL function, you can always time this in the MySQL client:
mysql> select benchmark(1000000,1+1); +------------------------+ | benchmark(1000000,1+1) | +------------------------+ | 0 | +------------------------+ 1 row in set (0.32 sec)
The above shows that MySQL can execute 1,000,000 + expressions
in 0.32 seconds on a PentiumII 400MHz.
All MySQL functions should be very optimised, but there may be some
exceptions, and the benchmark(loop_count,expression) is a great
tool to find out if this is a problem with your query.
EXPLAIN Syntax (Get Information About a
SELECT)EXPLAIN tbl_name or EXPLAIN SELECT select_options
EXPLAIN tbl_name is a synonym for DESCRIBE tbl_name
or SHOW COLUMNS FROM tbl_name.
When you precede a SELECT statement with the keyword
EXPLAIN, MySQL explains how it would process the
SELECT, providing information about how tables are joined and in
which order.
With the help of EXPLAIN, you can see when you must add indexes
to tables to get a faster SELECT that uses indexes to find the
records. You can also see if the optimiser joins the tables in an optimal order.
To force the optimiser to use a specific join order for a SELECT
statement, add a STRAIGHT_JOIN clause.
For non-simple joins, EXPLAIN returns a row of information for
each table used in the SELECT statement. The tables are listed in
the order they would be read. MySQL resolves all joins using a single-sweep
multi-join method. This means that MySQL reads a row from the first table, then
finds a matching row in the second table, then in the third table and so on.
When all tables are processed, it outputs the selected columns and backtracks
through the table list until a table is found for which there are more matching
rows. The next row is read from this table and the process continues with the
next table.
Output from EXPLAIN includes the following columns:
table
type
possible_keys
possible_keys column indicates which indexes MySQL could
use to find the rows in this table. Note that this column is totally
independent of the order of the tables. That means that some of the keys in
possible_keys may not be usable in practice with the generated table order. If
this column is empty, there are no relevant indexes. In this case, you may be
able to improve the performance of your query by examining the
WHERE clause to see if it refers to some column or columns that
would be suitable for indexing. If so, create an appropriate index and check
the query with EXPLAIN again. See section 6.5.4
ALTER TABLE Syntax. To see what indexes a table has, use
SHOW INDEX FROM tbl_name.
key
key column indicates the key that MySQL actually decided
to use. The key is NULL if no index was chosen. If MySQL chooses
the wrong index, you can probably force MySQL to use another index by using
myisamchk --analyze, See section 4.4.6.1
myisamchk Invocation Syntax, or by using USE
INDEX/IGNORE INDEX. See section 6.4.1.1
JOIN Syntax.
key_len
key_len column indicates the length of the key that MySQL
decided to use. The length is NULL if the key is
NULL. Note that this tells us how many parts of a multi-part key
MySQL will actually use.
ref
ref column shows which columns or constants are used with
the key to select rows from the table.
rows
rows column indicates the number of rows MySQL believes
it must examine to execute the query.
Extra
Distinct
Not exists
LEFT JOIN optimisation on the query
and will not examine more rows in this table for the previous row
combination after it finds one row that matches the LEFT JOIN
criteria. Here is an example for this: SELECT * FROM t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t2.id IS NULL;Assume that
t2.id is defined with NOT NULL.
In this case MySQL will scan t1 and look up the rows in
t2 through t1.id. If MySQL finds a matching row in
t2, it knows that t2.id can never be
NULL, and will not scan through the rest of the rows in
t2 that has the same id. In other words, for each
row in t1, MySQL only needs to do a single lookup in
t2, independent of how many matching rows there are in
t2.
range checked for each record (index map: #)Using filesort
join type and storing the sort key + pointer to the row for all
rows that match the WHERE. Then the keys are sorted. Finally
the rows are retrieved in sorted order.
Using index
Using temporary
ORDER BY on a
different column set than you did a GROUP BY on.
Where used
WHERE clause will be used to restrict which rows will be
matched against the next table or sent to the client. If you don't have this
information and the table is of type ALL or index,
you may have something wrong in your query (if you don't intend to
fetch/examine all rows from the table). Using
filesort and Using temporary. The different join types are listed below, ordered from best to worst type:
system
const join type.
const
const
tables are very fast as they are read only once!
eq_ref
const types. It is used when all parts of an index are used by
the join and the index is UNIQUE or a PRIMARY KEY.
ref
ref is used if the
join uses only a leftmost prefix of the key, or if the key is not
UNIQUE or a PRIMARY KEY (in other words, if the join
cannot select a single row based on the key value). If the key that is used
matches only a few rows, this join type is good.
range
key column indicates which index is used.
The key_len contains the longest key part that was used. The
ref column will be NULL for this type.
index
ALL, except that only the index tree is
scanned. This is usually faster than ALL, as the index file is
usually smaller than the data file.
ALL
const, and usually very bad in all other
cases. You normally can avoid ALL by adding more indexes, so that
the row can be retrieved based on constant values or column values from
earlier tables. You can get a good indication of how good a join is by multiplying all values
in the rows column of the EXPLAIN output. This should
tell you roughly how many rows MySQL must examine to execute the query. This
number is also used when you restrict queries with the
max_join_size variable. See section 5.5.2
Tuning Server Parameters.
The following example shows how a JOIN can be optimised
progressively using the information provided by EXPLAIN.
Suppose you have the SELECT statement shown below, that you
examine using EXPLAIN:
EXPLAIN SELECT tt.TicketNumber, tt.TimeIn,
tt.ProjectReference, tt.EstimatedShipDate,
tt.ActualShipDate, tt.ClientID,
tt.ServiceCodes, tt.RepetitiveID,
tt.CurrentProcess, tt.CurrentDPPerson,
tt.RecordVolume, tt.DPPrinted, et.COUNTRY,
et_1.COUNTRY, do.CUSTNAME
FROM tt, et, et AS et_1, do
WHERE tt.SubmitTime IS NULL
AND tt.ActualPC = et.EMPLOYID
AND tt.AssignedPC = et_1.EMPLOYID
AND tt.ClientID = do.CUSTNMBR;
For this example, assume that:
| Table | Column | Column type |
tt |
ActualPC |
CHAR(10) |
tt |
AssignedPC |
CHAR(10) |
tt |
ClientID |
CHAR(10) |
et |
EMPLOYID |
CHAR(15) |
do |
CUSTNMBR |
CHAR(15) |
| Table | Index |
tt |
ActualPC |
tt |
AssignedPC |
tt |
ClientID |
et |
EMPLOYID (primary key) |
do |
CUSTNMBR (primary key) |
tt.ActualPC values aren't evenly distributed. Initially, before any optimisations have been performed, the
EXPLAIN statement produces the following information:
table type possible_keys key key_len ref rows Extra
et ALL PRIMARY NULL NULL NULL 74
do ALL PRIMARY NULL NULL NULL 2135
et_1 ALL PRIMARY NULL NULL NULL 74
tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872
range checked for each record (key map: 35)
Because type is ALL for each table, this output
indicates that MySQL is doing a full join for all tables! This will take quite a
long time, as the product of the number of rows in each table must be examined!
For the case at hand, this is 74 * 2135 * 74 * 3872 =
45,268,558,720 rows. If the tables were bigger, you can only imagine how
long it would take.
One problem here is that MySQL can't (yet) use indexes on columns efficiently
if they are declared differently. In this context, VARCHAR and
CHAR are the same unless they are declared as different lengths.
Because tt.ActualPC is declared as CHAR(10) and
et.EMPLOYID is declared as CHAR(15), there is a length
mismatch.
To fix this disparity between column lengths, use ALTER TABLE to
lengthen ActualPC from 10 characters to 15 characters:
mysql> ALTER TABLE tt MODIFY ActualPC VARCHAR(15);
Now tt.ActualPC and et.EMPLOYID are both
VARCHAR(15). Executing the EXPLAIN statement again
produces this result:
table type possible_keys key key_len ref rows Extra
tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used
do ALL PRIMARY NULL NULL NULL 2135
range checked for each record (key map: 1)
et_1 ALL PRIMARY NULL NULL NULL 74
range checked for each record (key map: 1)
et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1
This is not perfect, but is much better (the product of the rows
values is now less by a factor of 74). This version is executed in a couple of
seconds.
A second alteration can be made to eliminate the column length mismatches for
the tt.AssignedPC = et_1.EMPLOYID and tt.ClientID =
do.CUSTNMBR comparisons:
mysql> ALTER TABLE tt MODIFY AssignedPC VARCHAR(15),
MODIFY ClientID VARCHAR(15);
Now EXPLAIN produces the output shown below:
table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 tt ref AssignedPC,ClientID,ActualPC ActualPC 15 et.EMPLOYID 52 where used et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
This is almost as good as it can get.
The remaining problem is that, by default, MySQL assumes that values in the
tt.ActualPC column are evenly distributed, and that isn't the case
for the tt table. Fortunately, it is easy to tell MySQL about this:
shell> myisamchk --analyze PATH_TO_MYSQL_DATABASE/tt shell> mysqladmin refresh
Now the join is perfect, and EXPLAIN produces this result:
table type possible_keys key key_len ref rows Extra tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1 et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
Note that the rows column in the output from
EXPLAIN is an educated guess from the MySQL join optimiser. To
optimise a query, you should check if the numbers are even close to the truth.
If not, you may get better performance by using STRAIGHT_JOIN in
your SELECT statement and trying to list the tables in a different
order in the FROM clause.
In most cases you can estimate the performance by counting disk seeks. For
small tables, you can usually find the row in 1 disk seek (as the index is
probably cached). For bigger tables, you can estimate that (using B++ tree
indexes) you will need: log(row_count) / log(index_block_length / 3 * 2 /
(index_length + data_pointer_length)) + 1 seeks to find a row.
In MySQL an index block is usually 1024 bytes and the data pointer is usually
4 bytes. A 500,000 row table with an index length of 3 (medium integer) gives
you: log(500,000)/log(1024/3*2/(3+4)) + 1 = 4 seeks.
As the above index would require about 500,000 * 7 * 3/2 = 5.2M, (assuming that the index buffers are filled to 2/3, which is typical) you will probably have much of the index in memory and you will probably only need 1-2 calls to read data from the OS to find the row.
For writes, however, you will need 4 seek requests (as above) to find where to place the new index and normally 2 seeks to update the index and write the row.
Note that the above doesn't mean that your application will slowly degenerate by N log N! As long as everything is cached by the OS or SQL server things will only go marginally slower while the table gets bigger. After the data gets too big to be cached, things will start to go much slower until your applications is only bound by disk-seeks (which increase by N log N). To avoid this, increase the index cache as the data grows. See section 5.5.2 Tuning Server Parameters.
SELECT QueriesIn general, when you want to make a slow SELECT ... WHERE
faster, the first thing to check is whether or not you can add an index. See
section 5.4.3
How MySQL Uses Indexes. All references between different tables should
usually be done with indexes. You can use the EXPLAIN command to
determine which indexes are used for a SELECT. See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
Some general tips:
myisamchk
--analyze on a table after it has been loaded with relevant data. This
updates a value for each index part that indicates the average number of rows
that have the same value. (For unique indexes, this is always 1, of course.)
MySQL will use this to decide which index to choose when you connect two
tables with 'a non-constant expression'. You can check the result from the
analyze run by doing SHOW INDEX FROM table_name and
examining the Cardinality column.
myisamchk
--sort-index --sort-records=1 (if you want to sort on index 1). If you
have a unique index from which you want to read all records in order according
to that index, this is a good way to make that faster. Note, however, that
this sorting isn't written optimally and will take a long time for a large
table! WHERE
ClausesThe WHERE optimisations are put in the SELECT part
here because they are mostly used with SELECT, but the same
optimisations apply for WHERE in DELETE and
UPDATE statements.
Also note that this section is incomplete. MySQL does many optimisations, and we have not had time to document them all.
Some of the optimisations performed by MySQL are listed below:
((a AND b) AND c OR (((a AND b) AND (c AND d)))) -> (a AND b AND c) OR (a AND b AND c AND d)
(a<b AND b=c) AND a=5 -> b>5 AND b=c AND a=5
(B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6) -> B=5 OR B=6
COUNT(*) on a single table without a WHERE is
retrieved directly from the table information for MyISAM and HEAP tables. This
is also done for any NOT NULL expression when used with only one
table.
SELECT statements are impossible and returns no rows.
HAVING is merged with WHERE if you don't use
GROUP BY or group functions (COUNT(),
MIN()...).
WHERE is constructed to get a
fast WHERE evaluation for each sub-join and also to skip records
as soon as possible.
WHERE clause on a
UNIQUE index, or a PRIMARY KEY, where all index
parts are used with constant expressions and the index parts are defined as
NOT NULL. mysql> SELECT * FROM t WHERE primary_key=1;
mysql> SELECT * FROM t1,t2
WHERE t1.primary_key=1 AND t2.primary_key=t1.id;
ORDER BY and in GROUP
BY come from the same table, then this table is preferred first when
joining.
ORDER BY clause and a different GROUP
BY clause, or if the ORDER BY or GROUP BY
contains columns from tables other than the first table in the join queue, a
temporary table is created.
SQL_SMALL_RESULT, MySQL will use an in-memory
temporary table.
HAVING clause are skipped. Some examples of queries that are very fast:
mysql> SELECT COUNT(*) FROM tbl_name;
mysql> SELECT MIN(key_part1),MAX(key_part1) FROM tbl_name;
mysql> SELECT MAX(key_part2) FROM tbl_name
WHERE key_part_1=constant;
mysql> SELECT ... FROM tbl_name
ORDER BY key_part1,key_part2,... LIMIT 10;
mysql> SELECT ... FROM tbl_name
ORDER BY key_part1 DESC,key_part2 DESC,... LIMIT 10;
The following queries are resolved using only the index tree (assuming the indexed columns are numeric):
mysql> SELECT key_part1,key_part2 FROM tbl_name WHERE key_part1=val;
mysql> SELECT COUNT(*) FROM tbl_name
WHERE key_part1=val1 AND key_part2=val2;
mysql> SELECT key_part2 FROM tbl_name GROUP BY key_part1;
The following queries use indexing to retrieve the rows in sorted order without a separate sorting pass:
mysql> SELECT ... FROM tbl_name ORDER BY key_part1,key_part2,... ; mysql> SELECT ... FROM tbl_name ORDER BY key_part1 DESC,key_part2 DESC,... ;
DISTINCTDISTINCT is converted to a GROUP BY on all columns,
DISTINCT combined with ORDER BY will in many cases
also need a temporary table.
When combining LIMIT # with DISTINCT, MySQL will
stop as soon as it finds # unique rows.
If you don't use columns from all used tables, MySQL will stop the scanning of the not used tables as soon as it has found the first match.
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;
In the case, assuming t1 is used before t2 (check with EXPLAIN),
then MySQL will stop reading from t2 (for that particular row in t1) when the
first row in t2 is found.
LEFT JOIN and
RIGHT JOINA LEFT JOIN B in MySQL is implemented as follows:
B is set to be dependent on table A
and all tables that A is dependent on.
A is set to be dependent on all tables (except
B) that are used in the LEFT JOIN condition.
LEFT JOIN conditions are moved to the WHERE
clause.
WHERE optimisations are done.
A that matches the WHERE
clause, but there wasn't any row in B that matched the LEFT
JOIN condition, then an extra B row is generated with all
columns set to NULL.
LEFT JOIN to find rows that don't exist in some
table and you have the following test: column_name IS NULL in the
WHERE part, where column_name is a column that is declared as
NOT NULL, then MySQL will stop searching after more rows (for a
particular key combination) after it has found one row that matches the
LEFT JOIN condition. RIGHT JOIN is implemented analogously as LEFT JOIN.
The table read order forced by LEFT JOIN and STRAIGHT
JOIN will help the join optimiser (which calculates in which order tables
should be joined) to do its work much more quickly, as there are fewer table
permutations to check.
Note that the above means that if you do a query of type:
SELECT * FROM a,b LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
MySQL will do a full scan on b as the LEFT JOIN
will force it to be read before d.
The fix in this case is to change the query to:
SELECT * FROM b,a LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
LIMITIn some cases MySQL will handle the query differently when you are using
LIMIT # and not using HAVING:
LIMIT, MySQL will
use indexes in some cases when it normally would prefer to do a full table
scan.
LIMIT # with ORDER BY, MySQL will end
the sorting as soon as it has found the first # lines instead of
sorting the whole table.
LIMIT # with DISTINCT, MySQL will
stop as soon as it finds # unique rows.
GROUP BY can be resolved by reading the key
in order (or do a sort on the key) and then calculate summaries until the key
value changes. In this case LIMIT # will not calculate any
unnecessary GROUP BY's.
# rows to the client, it
will abort the query (If you are not using SQL_CALC_FOUND_ROWS).
LIMIT 0 will always quickly return an empty set. This is
useful to check the query and to get the column types of the result columns.
LIMIT # to calculate
how much space is needed to resolve the query. INSERT QueriesThe time to insert a record consists approximately of:
where the numbers are somewhat proportional to the overall time. This does not take into consideration the initial overhead to open tables (which is done once for each concurrently running query).
The size of the table slows down the insertion of indexes by N log N (B-trees).
Some ways to speed up inserts:
INSERT statements. This is much faster (many
times in some cases) than using separate INSERT statements. If
you are adding data to non-empty table, you may tune up
myisam_bulk_insert_tree_size variable to make it even faster. See
section 4.5.6.4
SHOW VARIABLES.
INSERT DELAYED statement. See section
6.4.3
INSERT Syntax.
MyISAM tables you can insert rows at the same
time SELECTs are running if there are no deleted rows in the
tables.
LOAD DATA INFILE.
This is usually 20 times faster than using a lot of INSERT
statements. See section 6.4.9
LOAD DATA INFILE Syntax.
LOAD DATA INFILE
run even faster when the table has many indexes. Use the following procedure:
CREATE TABLE. For example,
using mysql or Perl-DBI.
FLUSH TABLES statement or the shell command
mysqladmin flush-tables.
myisamchk --keys-used=0 -rq /path/to/db/tbl_name. This
will remove all usage of all indexes from the table.
LOAD DATA INFILE. This will
not update any indexes and will therefore be very fast.
myisampack on it to make it smaller. See section 7.1.2.3
Compressed Table Characteristics.
myisamchk -r -q
/path/to/db/tbl_name. This will create the index tree in memory
before writing it to disk, which is much faster because it avoids lots of
disk seeks. The resulting index tree is also perfectly balanced.
FLUSH TABLES statement or the shell command
mysqladmin flush-tables. LOAD DATA
INFILE also does the above optimization if you insert into an empty
table; The main difference with the above procedure is that you can let
myisamchk allocate much more temporary memory for the index creation that you
may want MySQL to allocate for every index recreation. Since MySQL
4.0 you can also use ALTER TABLE tbl_name DISABLE KEYS
instead of myisamchk --keys-used=0 -rq /path/to/db/tbl_name and
ALTER TABLE tbl_name ENABLE KEYS instead of myisamchk -r -q
/path/to/db/tbl_name. This way you can also skip FLUSH
TABLES steps.
mysql> LOCK TABLES a WRITE; mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33); mysql> INSERT INTO a VALUES (8,26),(6,29); mysql> UNLOCK TABLES;The main speed difference is that the index buffer is flushed to disk only once, after all
INSERT statements have completed. Normally
there would be as many index buffer flushes as there are different
INSERT statements. Locking is not needed if you can insert all
rows with a single statement. For transactional tables, you should use
BEGIN/COMMIT instead of LOCK TABLES to get a
speedup. Locking will also lower the total time of multi-connection tests, but
the maximum wait time for some threads will go up (because they wait for
locks). For example: thread 1 does 1000 inserts thread 2, 3, and 4 does 1 insert thread 5 does 1000 insertsIf you don't use locking, 2, 3, and 4 will finish before 1 and 5. If you use locking, 2, 3, and 4 probably will not finish before 1 or 5, but the total time should be about 40% faster. As
INSERT, UPDATE,
and DELETE operations are very fast in MySQL, you will obtain
better overall performance by adding locks around everything that does more
than about 5 inserts or updates in a row. If you do very many inserts in a
row, you could do a LOCK TABLES followed by an UNLOCK
TABLES once in a while (about each 1000 rows) to allow other threads
access to the table. This would still result in a nice performance gain. Of
course, LOAD DATA INFILE is much faster for loading data.
To get some more speed for both LOAD DATA INFILE and
INSERT, enlarge the key buffer. See section 5.5.2
Tuning Server Parameters.
UPDATE QueriesUpdate queries are optimised as a SELECT query with the
additional overhead of a write. The speed of the write is dependent on the size
of the data that is being updated and the number of indexes that are updated.
Indexes that are not changed will not be updated.
Also, another way to get fast updates is to delay updates and then do many updates in a row later. Doing many updates in a row is much quicker than doing one at a time if you lock the table.
Note that, with dynamic record format, updating a record to a longer total
length may split the record. So if you do this often, it is very important to
OPTIMIZE TABLE sometimes. See section 4.5.1
OPTIMIZE TABLE Syntax.
DELETE QueriesIf you want to delete all rows in the table, you should use TRUNCATE
TABLE table_name. See section 6.4.7
TRUNCATE Syntax.
The time to delete a record is exactly proportional to the number of indexes. To delete records more quickly, you can increase the size of the index cache. See section 5.5.2 Tuning Server Parameters.
Unsorted tips for faster systems:
thread_cache_size variable. See section 5.5.2
Tuning Server Parameters.
EXPLAIN command.
See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
SELECT queries on MyISAM tables that are
updated a lot. This is to avoid problems with table locking.
MyISAM tables can insert rows in a table without
deleted rows at the same time another table is reading from it. If this is
important for you, you should consider methods where you don't have to delete
rows or run OPTIMIZE TABLE after you have deleted a lot of rows.
ALTER TABLE ... ORDER BY expr1,expr2... if you mostly
retrieve rows in expr1,expr2.. order. By using this option after big changes
to the table, you may be able to get higher performance.
SELECT * FROM table_name
WHERE hash=MD5(concat(col1,col2)) AND col_1='constant' AND
col_2='constant'
VARCHAR or BLOB columns. You will get dynamic row
length as soon as you are using a single VARCHAR or
BLOB column. See section 7
MySQL Table Types.
UPDATE
table set count=count+1 where index_column=constant is very fast! This
is really important when you use databases like MySQL that only have table
locking (multiple readers / single writers). This will also give better
performance with most databases, as the row locking manager in this case will
have less to do.
INSERT /*! DELAYED */ when you do not need to know when
your data is written. This speeds things up because many records can be
written with a single disk write.
INSERT /*! LOW_PRIORITY */ when you want your selects to
be more important.
SELECT /*! HIGH_PRIORITY */ to get selects that jump the
queue. That is, the select is done even if there is somebody waiting to do a
write.
INSERT statement to store many rows with
one SQL command (many SQL servers supports this).
LOAD DATA INFILE to load bigger amounts of data. This is
faster than normal inserts and will be even faster when myisamchk
is integrated in mysqld.
AUTO_INCREMENT columns to make unique values.
OPTIMIZE TABLE once in a while to avoid fragmentation
when using dynamic table format. See section 4.5.1
OPTIMIZE TABLE Syntax.
HEAP tables to get more speed when possible. See section
7
MySQL Table Types.
name instead of
customer_name in the customer table). To make your names portable
to other SQL servers you should keep them shorter than 18 characters.
MyISAM directly, you could get a
speed increase of 2-5 times compared to using the SQL interface. To be able to
do this the data must be on the same server as the application, and usually it
should only be accessed by one process (because external file locking is
really slow). One could eliminate the above problems by introducing low-level
MyISAM commands in the MySQL server (this could be one easy way
to get more performance if needed). By carefully designing the database
interface, it should be quite easy to support this types of optimisation.
DELAY_KEY_WRITE=1 will make the
updating of indexes faster, as these are not logged to disk until the file is
closed. The downside is that you should run myisamchk on these
tables before you start mysqld to ensure that they are okay if
something killed mysqld in the middle. As the key information can
always be generated from the data, you should not lose anything by using
DELAY_KEY_WRITE. You can find a discussion about different locking methods in the appendix. See section E.4 Locking methods.
All locking in MySQL is deadlock-free. This is managed by always requesting all needed locks at once at the beginning of a query and always locking the tables in the same order.
The locking method MySQL uses for WRITE locks works as follows:
The locking method MySQL uses for READ locks works as follows:
When a lock is released, the lock is made available to the threads in the write lock queue, then to the threads in the read lock queue.
This means that if you have many updates on a table, SELECT
statements will wait until there are no more updates.
To work around this for the case where you want to do many
INSERT and SELECT operations on a table, you can
insert rows in a temporary table and update the real table with the records from
the temporary table once in a while.
This can be done with the following code:
mysql> LOCK TABLES real_table WRITE, insert_table WRITE; mysql> insert into real_table select * from insert_table; mysql> TRUNCATE TABLE insert_table; mysql> UNLOCK TABLES;
You can use the LOW_PRIORITY options with INSERT,
UPDATE or DELETE or HIGH_PRIORITY with
SELECT if you want to prioritise retrieval in some specific cases.
You can also start mysqld with --low-priority-updates
to get the same behaveour.
Using SQL_BUFFER_RESULT can also help making table locks
shorter. See section 6.4.1
SELECT Syntax.
You could also change the locking code in `mysys/thr_lock.c' to use a single queue. In this case, write locks and read locks would have the same priority, which might help some applications.
The table locking code in MySQL is deadlock free.
MySQL uses table locking (instead of row locking or column locking) on all
table types, except BDB tables, to achieve a very high lock speed.
For large tables, table locking is much better than row locking for most
applications, but there are, of course, some pitfalls.
For InnoDB and BDB tables, MySQL only uses table
locking if you explicitely lock the table with LOCK TABLES or
execute a command that will modify every row in the table, like ALTER
TABLE. For these table types we recommend you to not use LOCK
TABLES at all.
In MySQL Version 3.23.7 and above, you can insert rows into
MyISAM tables at the same time other threads are reading from the
table. Note that currently this only works if there are no holes after deleted
rows in the table at the time the insert is made. When all holes has been filled
with new data, concurrent inserts will automatically be enabled again.
Table locking enables many threads to read from a table at the same time, but if a thread wants to write to a table, it must first get exclusive access. During the update, all other threads that want to access this particular table will wait until the update is ready.
As updates on tables normally are considered to be more important than
SELECT, all statements that update a table have higher priority
than statements that retrieve information from a table. This should ensure that
updates are not 'starved' because one issues a lot of heavy queries against a
specific table. (You can change this by using LOW_PRIORITY with the statement
that does the update or HIGH_PRIORITY with the SELECT
statement.)
Starting from MySQL Version 3.23.7 one can use the
max_write_lock_count variable to force MySQL to temporary give all
SELECT statements, that wait for a table, a higher priority after a
specific number of inserts on a table.
Table locking is, however, not very good under the following senario:
SELECT that takes a long time to run.
UPDATE on a used table. This
client will wait until the SELECT is finished.
SELECT statement on the same
table. As UPDATE has higher priority than SELECT,
this SELECT will wait for the UPDATE to finish. It
will also wait for the first SELECT to finish!
full disk, in which
case all threads that wants to access the problem table will also be put in a
waiting state until more disk space is made available. Some possible solutions to this problem are:
SELECT statements to run faster. You may have
to create some summary tables to do this.
mysqld with --low-priority-updates. This
will give all statements that update (modify) a table lower priority than a
SELECT statement. In this case the last SELECT
statement in the previous scenario would execute before the
INSERT statement.
INSERT, UPDATE, or
DELETE statement lower priority with the
LOW_PRIORITY attribute.
mysqld with a low value for
max_write_lock_count to give READ locks after a
certain number of WRITE locks.
SET
SQL_LOW_PRIORITY_UPDATES=1. See section 5.5.6
SET Syntax.
SELECT is very important with
the HIGH_PRIORITY attribute. See section 6.4.1
SELECT Syntax.
INSERT combined with
SELECT, switch to use the new MyISAM tables as these
support concurrent SELECTs and INSERTs.
INSERT and SELECT statements,
the DELAYED attribute to INSERT will probably solve
your problems. See section 6.4.3
INSERT Syntax.
SELECT and DELETE, the
LIMIT option to DELETE may help. See section 6.4.6
DELETE Syntax. MySQL keeps row data and index data in separate files. Many (almost all) other databases mix row and index data in the same file. We believe that the MySQL choice is better for a very wide range of modern systems.
Another way to store the row data is to keep the information for each column in a separate area (examples are SDBM and Focus). This will cause a performance hit for every query that accesses more than one column. Because this degenerates so quickly when more than one column is accessed, we believe that this model is not good for general purpose databases.
The more common case is that the index and data are stored together (like in Oracle/Sybase et al). In this case you will find the row information at the leaf page of the index. The good thing with this layout is that it, in many cases, depending on how well the index is cached, saves a disk read. The bad things with this layout are:
One of the most basic optimisation is to get your data (and indexes) to take as little space on the disk (and in memory) as possible. This can give huge improvements because disk reads are faster and normally less main memory will be used. Indexing also takes less resources if done on smaller columns.
MySQL supports a lot of different table types and row formats. Choosing the right table format may give you a big performance gain. See section 7 MySQL Table Types.
You can get better performance on a table and minimise storage space using the techniques listed below:
MEDIUMINT is often better than INT.
NOT NULL if possible. It makes
everything faster and you save one bit per column. Note that if you really
need NULL in your application you should definitely use it. Just
avoid having it on all columns by default.
VARCHAR,
TEXT, or BLOB columns), a fixed-size record format
is used. This is faster but unfortunately may waste some space. See section 7.1.2
MyISAM Table Formats.
Indexes are used to find rows with a specific value of one column fast. Without an index MySQL has to start with the first record and then read through the whole table until it finds the relevant rows. The bigger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly get a position to seek to in the middle of the data file without having to look at all the data. If a table has 1000 rows, this is at least 100 times faster than reading sequentially. Note that if you need to access almost all 1000 rows it is faster to read sequentially because we then avoid disk seeks.
All MySQL indexes (PRIMARY, UNIQUE, and
INDEX) are stored in B-trees. Strings are automatically prefix- and
end-space compressed. See section 6.5.7
CREATE INDEX Syntax.
Indexes are used to:
WHERE clause.
MAX() or MIN() value for a specific
indexed column. This is optimised by a preprocessor that checks if you are
using WHERE key_part_# = constant on all key parts < N. In
this case MySQL will do a single key lookup and replace the MIN()
expression with a constant. If all expressions are replaced with constants,
the query will return at once: SELECT MIN(key_part2),MAX(key_part2) FROM table_name where key_part1=10
ORDER BY key_part_1,key_part_2
). The key is read in reverse order if all key parts are followed by
DESC. The index can also be used even if the ORDER
BY doesn't match the index exactly, as long as all the unused index
parts and all the extra are ORDER BY columns are constants in the
WHERE clause. The following queries will use the index to resolve
the ORDER BY part: SELECT * FROM foo ORDER BY key_part1,key_part2,key_part3; SELECT * FROM foo WHERE column=constant ORDER BY column, key_part1; SELECT * FROM foo WHERE key_part1=const GROUP BY key_part2;
SELECT key_part3 FROM table_name WHERE key_part1=1
Suppose you issue the following SELECT statement:
mysql> SELECT * FROM tbl_name WHERE col1=val1 AND col2=val2;
If a multiple-column index exists on col1 and col2,
the appropriate rows can be fetched directly. If separate single-column indexes
exist on col1 and col2, the optimiser tries to find
the most restrictive index by deciding which index will find fewer rows and
using that index to fetch the rows.
If the table has a multiple-column
index, any leftmost prefix of the index can be used by the optimiser to find
rows. For example, if you have a three-column index on
(col1,col2,col3), you have indexed search capabilities on
(col1), (col1,col2), and
(col1,col2,col3).
MySQL can't use a partial index if the columns don't form a leftmost prefix
of the index. Suppose you have the SELECT statements shown below:
mysql> SELECT * FROM tbl_name WHERE col1=val1; mysql> SELECT * FROM tbl_name WHERE col2=val2; mysql> SELECT * FROM tbl_name WHERE col2=val2 AND col3=val3;
If an index exists on (col1,col2,col3), only the first query
shown above uses the index. The second and third queries do involve indexed
columns, but (col2) and (col2,col3) are not leftmost
prefixes of (col1,col2,col3).
MySQL also uses indexes for LIKE comparisons if the
argument to LIKE is a constant string that doesn't start with a
wild-card character. For example, the following SELECT statements
use indexes:
mysql> select * from tbl_name where key_col LIKE "Patrick%"; mysql> select * from tbl_name where key_col LIKE "Pat%_ck%";
In the first statement, only rows with "Patrick" <= key_col <
"Patricl" are considered. In the second statement, only rows with
"Pat" <= key_col < "Pau" are considered.
The following SELECT statements will not use indexes:
mysql> select * from tbl_name where key_col LIKE "%Patrick%"; mysql> select * from tbl_name where key_col LIKE other_col;
In the first statement, the LIKE value begins with a wild-card
character. In the second statement, the LIKE value is not a
constant.
Searching using column_name IS
NULL will use indexes if column_name is an index.
MySQL normally uses the index that finds the least number of rows. An index
is used for columns that you compare with the following operators:
=, >, >=, <,
<=, BETWEEN, and a LIKE with a
non-wild-card prefix like 'something%'.
Any index that doesn't span all AND levels in the
WHERE clause is not used to optimise the query. In other words: To
be able to use an index, a prefix of the index must be used in every
AND group.
The following WHERE clauses use indexes:
... WHERE index_part1=1 AND index_part2=2 AND other_column=3
... WHERE index=1 OR A=10 AND index=2 /* index = 1 OR index = 2 */
... WHERE index_part1='hello' AND index_part_3=5
/* optimised like "index_part1='hello'" */
... WHERE index1=1 and index2=2 or index1=3 and index3=3;
/* Can use index on index1 but not on index2 or index 3 */
These WHERE clauses do NOT use indexes:
... WHERE index_part2=1 AND index_part3=2 /* index_part_1 is not used */ ... WHERE index=1 OR A=10 /* Index is not used in both AND parts */ ... WHERE index_part1=1 OR index_part2=10 /* No index spans all rows */
Note that in some cases MySQL will not use an index, even if one would be available. Some of the cases where this happens are:
LIMIT to only retrieve part of the rows, MySQL will use an index
anyway, as it can much more quickly find the few rows to return in the result.
All MySQL column types can be indexed. Use of indexes on the relevant columns
is the best way to improve the performance of SELECT operations.
The maximum number of keys and the maximum index length is defined per table handler. See section 7 MySQL Table Types. You can with all table handlers have at least 16 keys and a total index length of at least 256 bytes.
For CHAR and VARCHAR columns, you can index a
prefix of a column. This is much faster and requires less disk space than
indexing the whole column. The syntax to use in the CREATE TABLE
statement to index a column prefix looks like this:
KEY index_name (col_name(length))
The example below creates an index for the first 10 characters of the
name column:
mysql> CREATE TABLE test (
name CHAR(200) NOT NULL,
KEY index_name (name(10)));
For BLOB and TEXT columns, you must index a prefix
of the column. You cannot index the entire column.
In MySQL Version 3.23.23 or later, you can also create special
FULLTEXT indexes. They are used for full-text search. Only the
MyISAM table type supports FULLTEXT indexes. They can
be created only from VARCHAR and TEXT columns.
Indexing always happens over the entire column and partial indexing is not
supported. See section 6.8
MySQL Full-text Search for details.
MySQL can create indexes on multiple columns. An index may consist of up to
15 columns. (On CHAR and VARCHAR columns you can also
use a prefix of the column as a part of an index.)
A multiple-column index can be considered a sorted array containing values that are created by concatenating the values of the indexed columns.
MySQL uses multiple-column indexes in such a way that queries are fast when
you specify a known quantity for the first column of the index in a
WHERE clause, even if you don't specify values for the other
columns.
Suppose a table is created using the following specification:
mysql> CREATE TABLE test (
id INT NOT NULL,
last_name CHAR(30) NOT NULL,
first_name CHAR(30) NOT NULL,
PRIMARY KEY (id),
INDEX name (last_name,first_name));
Then the index name is an index over last_name and
first_name. The index will be used for queries that specify values
in a known range for last_name, or for both last_name
and first_name. Therefore, the name index will be used
in the following queries:
mysql> SELECT * FROM test WHERE last_name="Widenius";
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND first_name="Michael";
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND (first_name="Michael" OR first_name="Monty");
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND first_name >="M" AND first_name < "N";
However, the name index will NOT be used in the following
queries:
mysql> SELECT * FROM test WHERE first_name="Michael";
mysql> SELECT * FROM test WHERE last_name="Widenius"
OR first_name="Michael";
For more information on the manner in which MySQL uses indexes to improve query performance, see section 5.4.3 How MySQL Uses Indexes.
When you run mysqladmin status, you'll see something like this:
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
This can be somewhat perplexing if you only have 6 tables.
MySQL is multithreaded, so it may have many queries on the same table simultaneously. To minimise the problem with two threads having different states on the same file, the table is opened independently by each concurrent thread. This takes some memory but will normaly increase performance. Wth ISAM and MyISAM tables this also requires one extra file descriptor for the data file. With these table types the index file descriptor is shared between all threads.
You can read more about this topic in the next section. See section 5.4.7 How MySQL Opens and Closes Tables.
table_cache, max_connections, and
max_tmp_tables affect the maximum number of files the server keeps
open. If you increase one or both of these values, you may run up against a
limit imposed by your operating system on the per-process number of open file
descriptors. However, you can increase the limit on many systems. Consult your
OS documentation to find out how to do this, because the method for changing the
limit varies widely from system to system.
table_cache is related to max_connections. For
example, for 200 concurrent running connections, you should have a table cache
of at least 200 * n, where n is the maximum number of
tables in a join. You also need to reserve some extra file descriptors for
temporary tables and files.
Make sure that your operating system can handle the number of open file
descriptors implied by the table_cache setting. If
table_cache is set too high, MySQL may run out of file descriptors
and refuse connections, fail to perform queries, and be very unreliable. You
also have to take into account that the MyISAM table handler needs two file
descriptors for each unique open table. You can in increase the number of file
descriptors available for MySQL with the --open-files-limit=#
startup option. See section A.2.16
File Not Found.
The cache of open tables will be keept at a level of table_cache
entries (default 64; this can be changed with the -O table_cache=#
option to mysqld). Note that in MySQL may temporarly open even more
tables to be able to execute queries.
A not used table is closed and removed from the table cache under the following circumstances:
table_cache entires and a
thread is not anymore using a table.
mysqladmin refresh or mysqladmin
flush-tables.
When the table cache fills up, the server uses the following procedure to locate a cache entry to use:
A table is opened for each concurrent access. This means that if you have two
threads accessing the same table or access the table twice in the same query
(with AS) the table needs to be opened twice. The first open of any
table takes two file descriptors; each additional use of the table takes only
one file descriptor. The extra descriptor for the first open is used for the
index file; this descriptor is shared among all threads.
If you are opening a table with the HANDLER table_name OPEN
statement, a dedicated table object is allocated for the thread. This table
object is not shared by other threads an will not be closed until the thread
calls HANDLER table_name CLOSE or the thread dies. See section 6.4.2
HANDLER Syntax. When this happens, the table is put back in the
table_cache (if it isn't full).
You can check if your table cache is too small by checking the mysqld
variable Opened_tables. If this is quite big, even if you haven't
done a lot of FLUSH TABLES, you should increase your table cache.
See section 4.5.6.3
SHOW STATUS.
If you have many files in a directory, open, close, and create operations
will be slow. If you execute SELECT statements on many different
tables, there will be a little overhead when the table cache is full, because
for every table that has to be opened, another must be closed. You can reduce
this overhead by making the table cache larger.
We start with the system level things since some of these decisions have to be made very early. In other cases a fast look at this part may suffice because it not that important for the big gains. However, it is always nice to have a feeling about how much one could gain by changing things at this level.
The default OS to use is really important! To get the most use of multiple CPU machines one should use Solaris (because the threads works really nice) or Linux (because the 2.2 kernel has really good SMP support). Also on 32-bit machines Linux has a 2G file size limit by default. Hopefully this will be fixed soon when new filesystems are released (XFS/Reiserfs). If you have a desperate need for files bigger than 2G on Linux-intel 32 bit, you should get the LFS patch for the ext2 file system.
Because we have not run MySQL in production on that many platforms, we advice you to test your intended platform before choosing it, if possible.
--skip-locking MySQL option to avoid external
locking. Note that this will not impact MySQL's functionality as long as you
only run one server. Just remember to take down the server (or lock relevant
parts) before you run myisamchk. On some system this switch is
mandatory because the external locking does not work in any case. The
--skip-locking option is on by default when compiling with
MIT-pthreads, because flock() isn't fully supported by
MIT-pthreads on all platforms. It's also on default for Linux as Linux file
locking are not yet safe. The only case when you can't use
--skip-locking is if you run multiple MySQL servers (not
clients) on the same data, or run myisamchk on the table without
first flushing and locking the mysqld server tables first. You
can still use LOCK TABLES/UNLOCK TABLES even if you
are using --skip-locking You can get the default buffer sizes used by the mysqld server
with this command:
shell> mysqld --help
This command produces a list of all
mysqld options and configurable variables. The output includes the
default values and looks something like this:
Possible variables for option --set-variable (-O) are: back_log current value: 5 bdb_cache_size current value: 1048540 binlog_cache_size current_value: 32768 connect_timeout current value: 5 delayed_insert_timeout current value: 300 delayed_insert_limit current value: 100 delayed_queue_size current value: 1000 flush_time current value: 0 interactive_timeout current value: 28800 join_buffer_size current value: 131072 key_buffer_size current value: 1048540 lower_case_table_names current value: 0 long_query_time current value: 10 max_allowed_packet current value: 1048576 max_binlog_cache_size current_value: 4294967295 max_connections current value: 100 max_connect_errors current value: 10 max_delayed_threads current value: 20 max_heap_table_size current value: 16777216 max_join_size current value: 4294967295 max_sort_length current value: 1024 max_tmp_tables current value: 32 max_write_lock_count current value: 4294967295 myisam_sort_buffer_size current value: 8388608 net_buffer_length current value: 16384 net_retry_count current value: 10 net_read_timeout current value: 30 net_write_timeout current value: 60 query_buffer_size current value: 0 record_buffer current value: 131072 record_rnd_buffer current value: 131072 slow_launch_time current value: 2 sort_buffer current value: 2097116 table_cache current value: 64 thread_concurrency current value: 10 tmp_table_size current value: 1048576 thread_stack current value: 131072 wait_timeout current value: 28800
If there is a mysqld server currently running, you can see what
values it actually is using for the variables by executing this command:
shell> mysqladmin variables
You can find a full description for all variables in the SHOW
VARIABLES section in this manual. See section 4.5.6.4
SHOW VARIABLES.
You can also see some statistics from a running server by issuing the command
SHOW STATUS. See section 4.5.6.3
SHOW STATUS.
MySQL uses algorithms that are very scalable, so you can usually run with very little memory. If you, however, give MySQL more memory, you will normally also get better performance.
When tuning a MySQL server, the two most important variables to use are
key_buffer_size and table_cache. You should first feel
confident that you have these right before trying to change any of the other
variables.
If you have much memory (>=256M) and many tables and want maximum performance with a moderate number of clients, you should use something like this:
shell> safe_mysqld -O key_buffer=64M -O table_cache=256 \
-O sort_buffer=4M -O record_buffer=1M &
If you have only 128M and only a few tables, but you still do a lot of sorting, you can use something like:
shell> safe_mysqld -O key_buffer=16M -O sort_buffer=1M
If you have little memory and lots of connections, use something like this:
shell> safe_mysqld -O key_buffer=512k -O sort_buffer=100k \
-O record_buffer=100k &
or even:
shell> safe_mysqld -O key_buffer=512k -O sort_buffer=16k \
-O table_cache=32 -O record_buffer=8k -O net_buffer=1K &
If you are doing a GROUP BY or ORDER BY on files
that are much bigger than your available memory you should increase the value of
record_rnd_buffer to speed up the reading of rows after the sorting
is done.
When you have installed MySQL, the `support-files' directory will
contain some different my.cnf example files,
`my-huge.cnf', `my-large.cnf', `my-medium.cnf', and
`my-small.cnf', you can use as a base to optimise your system.
If there are very many connections, ``swapping problems'' may occur unless
mysqld has been configured to use very little memory for each
connection. mysqld performs better if you have enough memory for
all connections, of course.
Note that if you change an option to mysqld, it remains in
effect only for that instance of the server.
To see the effects of a parameter change, do something like this:
shell> mysqld -O key_buffer=32m --help
Make sure that the --help option is last; otherwise, the effect
of any options listed after it on the command line will not be reflected in the
output.
Most of the following tests are done on Linux with the MySQL benchmarks, but they should give some indication for other operating systems and workloads.
You get the fastest executable when you link with -static.
On Linux, you will get the fastest code when compiling with pgcc
and -O3. To compile `sql_yacc.cc' with these options, you
need about 200M memory because gcc/pgcc needs a lot of memory to
make all functions inline. You should also set CXX=gcc when
configuring MySQL to avoid inclusion of the libstdc++ library (it
is not needed). Note that with some versions of pgcc, the resulting
code will only run on true Pentium processors, even if you use the compiler
option that you want the resulting code to be working on all x586 type
processors (like AMD).
By just using a better compiler and/or better compiler options you can get a 10-30 % speed increase in your application. This is particularly important if you compile the SQL server yourself!
We have tested both the Cygnus CodeFusion and Fujitsu compilers, but when we tested them, neither was sufficiently bug free to allow MySQL to be compiled with optimisations on.
When you compile MySQL you should only include support for the character sets
that you are going to use. (Option --with-charset=xxx.) The
standard MySQL binary distributions are compiled with support for all character
sets.
Here is a list of some measurements that we have done:
pgcc and compile everything with -O6,
the mysqld server is 1% faster than with gcc 2.95.2.
-static), the result is 13%
slower on Linux. Note that you still can use a dynamic linked MySQL library.
It is only the server that is critical for performance.
mysqld binary with strip
libexec/mysqld, the resulting binary can be up to 4 % faster.
localhost,
MySQL will, by default, use sockets.)
--with-debug=full, then you will loose 20
% for most queries, but some queries may take substantially longer (The MySQL
benchmarks ran 35 % slower) If you use --with-debug, then you
will only loose 15 %. By starting a mysqld version compiled with
--with-debug=full with --skip-safemalloc the end
result should be close to when configuring with --with-debug.
gcc 2.95.2.
gcc 2.95.2 for ultrasparc with the option
-mcpu=v8 -Wa,-xarch=v8plusa gives 4 % more performance.
--log-bin makes [MySQL 1 %
slower.
-fomit-frame-pointer or -fomit-frame-pointer
-ffixed-ebp mysqld 1-4% faster. The MySQL-Linux distribution provided by MySQL AB used to be compiled with
pgcc, but we had to go back to regular gcc because of a bug in
pgcc that would generate the code that does not run on AMD. We will
continue using gcc until that bug is resolved. In the meantime, if you have a
non-AMD machine, you can get a faster binary by compiling with
pgcc. The standard MySQL Linux binary is linked statically to get
it faster and more portable.
The list below indicates some of the ways that the mysqld server
uses memory. Where applicable, the name of the server variable relevant to the
memory use is given:
key_buffer_size) is shared by all
threads; Other buffers used by the server are allocated as needed. See section
5.5.2
Tuning Server Parameters.
thread_stack), a connection buffer (variable
net_buffer_length), and a result buffer (variable
net_buffer_length). The connection buffer and result buffer are
dynamically enlarged up to max_allowed_packet when needed. When a
query is running, a copy of the current query string is also allocated.
record_buffer).
record_rnd_buffer).
BLOB columns are stored on disk. One
problem in MySQL versions before Version 3.23.2 is that if a HEAP table
exceeds the size of tmp_table_size, you get the error The
table tbl_name is full. In newer versions this is handled by
automatically changing the in-memory (HEAP) table to a disk-based (MyISAM)
table as necessary. To work around this problem, you can increase the
temporary table size by setting the tmp_table_size option to
mysqld, or by setting the SQL option SQL_BIG_TABLES
in the client program. See section 5.5.6
SET Syntax. In MySQL Version 3.20, the maximum size of the
temporary table was record_buffer*16, so if you are using this
version, you have to increase the value of record_buffer. You can
also start mysqld with the --big-tables option to
always store temporary tables on disk. However, this will affect the speed of
many complicated queries.
malloc() and
free()).
3 * n is
allocated (where n is the maximum row length, not counting
BLOB columns). A BLOB uses 5 to 8 bytes plus the
length of the BLOB data. The
ISAM/MyISAM table handlers will use one extra row
buffer for internal usage.
BLOB columns, a buffer is enlarged
dynamically to read in larger BLOB values. If you scan a table, a
buffer as large as the largest BLOB value is allocated.
mysqladmin flush-tables command closes all tables that are
not in use and marks all in-use tables to be closed when the currently
executing thread finishes. This will effectively free most in-use memory.
ps and other system status programs may report that
mysqld uses a lot of memory. This may be caused by thread-stacks on
different memory addresses. For example, the Solaris version of ps
counts the unused memory between stacks as used memory. You can verify this by
checking available swap with swap -s. We have tested
mysqld with commercial memory-leakage detectors, so there should be
no memory leaks.
When a new thread connects to mysqld, mysqld will
span a new thread to handle the request. This thread will first check if the
hostname is in the hostname cache. If not the thread will call
gethostbyaddr_r() and gethostbyname_r() to resolve the
hostname.
If the operating system doesn't support the above thread-safe calls, the
thread will lock a mutex and call gethostbyaddr() and
gethostbyname() instead. Note that in this case no other thread can
resolve other hostnames that is not in the hostname cache until the first thread
is ready.
You can disable DNS host lookup by starting mysqld with
--skip-name-resolve. In this case you can however only use IP names
in the MySQL privilege tables.
If you have a very slow DNS and many hosts, you can get more performance by
either disabling DNS lookop with --skip-name-resolve or by
increasing the HOST_CACHE_SIZE define (default: 128) and recompile
mysqld.
You can disable the hostname cache with --skip-host-cache. You
can clear the hostname cache with FLUSH HOSTS or mysqladmin
flush-hosts.
If you don't want to allow connections over TCP/IP, you can do
this by starting mysqld with --skip-networking.
SET SyntaxSET [OPTION] SQL_VALUE_OPTION= value, ...
SET OPTION sets various options that affect the operation of the
server or your client. Any option you set remains in effect until the current
session ends, or until you set the option to a different value.
CHARACTER SET character_set_name | DEFAULT
character_set_name is
cp1251_koi8, but you can easily add new mappings by editing the
`sql/convert.cc' file in the MySQL source distribution. The default
mapping can be restored by using a character_set_name value of
DEFAULT. Note that the syntax for setting the CHARACTER
SET option differs from the syntax for setting the other options.
PASSWORD = PASSWORD('some password')
PASSWORD FOR user = PASSWORD('some password')
mysql database can do this. The user
should be given in user@hostname format, where user
and hostname are exactly as they are listed in the
User and Host columns of the mysql.user
table entry. For example, if you had an entry with User and
Host fields of 'bob' and '%.loc.gov',
you would write: mysql> SET PASSWORD FOR bob@"%.loc.gov" = PASSWORD("newpass");
or
mysql> UPDATE mysql.user SET password=PASSWORD("newpass") where user="bob' and host="%.loc.gov";
SQL_AUTO_IS_NULL = 0 | 1
1 (default) then one can find the last inserted row
for a table with an auto_increment row with the following construct:
WHERE auto_increment_column IS NULL. This is used by some ODBC
programs like Access.
AUTOCOMMIT= 0 | 1
1 all changes to a table will be done at once. To
start a multi-command transaction, you have to use the BEGIN
statement. See section 6.7.1
BEGIN/COMMIT/ROLLBACK Syntax. If set to 0 you
have to use COMMIT / ROLLBACK to accept/revoke that
transaction. See section 6.7.1
BEGIN/COMMIT/ROLLBACK Syntax. Note that when you change from
not AUTOCOMMIT mode to AUTOCOMMIT mode, MySQL will
do an automatic COMMIT on any open transactions.
SQL_BIG_TABLES = 0 | 1
1, all temporary tables are
stored on disk rather than in memory. This will be a little slower, but you
will not get the error The table tbl_name is full for big
SELECT operations that require a large temporary table. The
default value for a new connection is 0 (that is, use in-memory
temporary tables).
SQL_BIG_SELECTS = 0 | 1
0, MySQL will abort if a SELECT is
attempted that probably will take a very long time. This is useful when an
inadvisable WHERE statement has been issued. A big query is
defined as a SELECT that probably will have to examine more than
max_join_size rows. The default value for a new connection is
1 (which will allow all SELECT statements).
SQL_BUFFER_RESULT = 0 | 1
SQL_BUFFER_RESULT will force the result from
SELECT's to be put into a temporary table. This will help MySQL
free the table locks early and will help in cases where it takes a long time
to send the result set to the client.
SQL_LOW_PRIORITY_UPDATES = 0 | 1
1, all INSERT, UPDATE,
DELETE, and and LOCK TABLE WRITE statements wait
until there is no pending SELECT or LOCK TABLE READ
on the affected table.
SQL_MAX_JOIN_SIZE = value | DEFAULT
SELECTs that will probably need to examine more
than value row combinations. By setting this value, you can catch
SELECTs where keys are not used properly and that would probably
take a long time. Setting this to a value other than DEFAULT will
reset the SQL_BIG_SELECTS flag. If you set the
SQL_BIG_SELECTS flag again, the SQL_MAX_JOIN_SIZE
variable will be ignored. You can set a default value for this variable by
starting mysqld with -O max_join_size=#.
SQL_QUERY_CACHE_TYPE = OFF | ON | DEMAND
SQL_QUERY_CACHE_TYPE = 0 | 1 | 2
| Option | Description |
| 0 or OFF | Don't cache or retrieve results. |
| 1 or ON | Cache all results except SELECT SQL_NO_CACHE ...
queries. |
| 2 or DEMAND | Cache only SELECT SQL_CACHE ... queries.
|
SQL_SAFE_UPDATES = 0 | 1
1, MySQL will abort if an UPDATE or
DELETE is attempted that doesn't use a key or LIMIT
in the WHERE clause. This makes it possible to catch wrong
updates when creating SQL commands by hand.
SQL_SELECT_LIMIT = value | DEFAULT
SELECT
statements. If a SELECT has a LIMIT clause, the
LIMIT takes precedence over the value of
SQL_SELECT_LIMIT. The default value for a new connection is
``unlimited.'' If you have changed the limit, the default value can be
restored by using a SQL_SELECT_LIMIT value of
DEFAULT.
SQL_LOG_OFF = 0 | 1
1, no logging will be done to the standard log for
this client, if the client has the process privilege. This
does not affect the update log!
SQL_LOG_UPDATE = 0 | 1
0, no logging will be done to the update log for
the client, if the client has the process privilege. This
does not affect the standard log!
SQL_QUOTE_SHOW_CREATE = 0 | 1
1, SHOW CREATE TABLE will quote table
and column names. This is on by default, for replication of
tables with fancy column names to work. section 4.5.6.8
SHOW CREATE TABLE.
TIMESTAMP = timestamp_value | DEFAULT
timestamp_value should
be a Unix epoch timestamp, not a MySQL timestamp.
LAST_INSERT_ID = #
LAST_INSERT_ID(). This is
stored in the update log when you use LAST_INSERT_ID() in a
command that updates a table.
INSERT_ID = #
INSERT or
ALTER TABLE command when inserting an AUTO_INCREMENT
value. This is mainly used with the update log. See section 6.7.3
SET TRANSACTION Syntax.
hdparm -m 16 -d 1Note that the performance/reliability when using the above depends on your hardware, so we strongly suggest that you test your system thoroughly after using
hdparm! Please consult the hdparm man
page for more information! If hdparm is not used wisely,
filesystem corruption may result. Backup everything before experimenting!
You can move tables and databases from the database directory to other locations and replace them with symbolic links to the new locations. You might want to do this, for example, to move a database to a file system with more free space or increase the speed of your system by spreading your tables to different disk.
The recommended may to do this, is to just symlink databases to different disk and only symlink tables as a last resort.
The way to symlink a database is to first create a directory on some disk where you have free space and then create a symlink to it from the MySQL database directory.
shell> mkdir /dr1/databases/test shell> ln -s /dr1/databases/test mysqld-datadir
MySQL doesn't support that you link one directory to multiple databases.
Replacing a database directory with a symbolic link will work fine as long as
you don't make a symbolic link between databases. Suppose you have a database
db1 under the MySQL data directory, and then make a symlink
db2 that points to db1:
shell> cd /path/to/datadir shell> ln -s db1 db2
Now, for any table tbl_a in db1, there also appears
to be a table tbl_a in db2. If one thread updates
db1.tbl_a and another thread updates db2.tbl_a, there
will be problems.
If you really need this, you must change the following code in `mysys/mf_format.c':
if (flag & 32 || (!lstat(to,&stat_buff) && S_ISLNK(stat_buff.st_mode)))
to
if (1)
On Windows you can use internal symbolic links to directories by compiling
MySQL with -DUSE_SYMDIR. This allows you to put different databases
on different disks. See section 2.6.2.5
Splitting Data Across Different Disks on Windows.
Before MySQL 4.0 you should not symlink tables, if you are not very careful
with them. The problem is that if you run ALTER TABLE, REPAIR
TABLE or OPTIMIZE TABLE on a symlinked table, the symlinks
will be removed and replaced by the original files. This happens because the
above command works by creating a temporary file in the database directory and
when the command is complete, replace the original file with the temporary file.
You should not symlink tables on system that doesn't have a fully working
realpath() call. (At least Linux and Solaris support
realpath())
In MySQL 4.0 symlinks is only fully supported for MyISAM tables.
For other table types you will probably get strange problems when doing any of
the above mentioned commands.
The handling of symbolic links in MySQL 4.0 works the following way (this is
mostly relevant only for MyISAM tables).
mysqld is not running) or with the INDEX/DATA
DIRECTORY="path-to-dir" command in CREATE TABLE. See
section 6.5.3
CREATE TABLE Syntax.
myisamchk will not replace a symlink with the index/file but
work directly on the files the symlinks points to. Any temporary files will be
created in the same directory where the data/index file is.
mysqld as root and not allow persons to
have write access to the MySQL database directories.
ALTER TABLE RENAME and you don't
change database, the symlink in the database directory will be renamed to the
new name and the data/index file will be renamed accordingly.
ALTER TABLE RENAME to move a table to another
database, then the table will be moved to the other database directory and the
old symlinks and the files they pointed to will be deleted.
--skip-symlink option to mysqld to ensure that no
one can drop or rename a file outside of the mysqld data
directory. Things that are not yet supported:
ALTER TABLE ignores all INDEX/DATA
DIRECTORY="path" options.
CREATE TABLE doesn't report if the table has symbolic links.
mysqldump doesn't include the symbolic links information in
the output.
BACKUP TABLE and RESTORE TABLE don't respect
symbolic links. MySQL has a very complex, but intuitive and easy to learn SQL interface. This chapter describes the various commands, types, and functions you will need to know in order to use MySQL efficiently and effectively. This chapter also serves as a reference to all functionality included in MySQL. In order to use this chapter effectively, you may find it useful to refer to the various indexes.
This section describes the various ways to write strings and numbers in MySQL. It also covers the various nuances and ``gotchas'' that you may run into when dealing with these basic types in MySQL.
A string is a sequence of characters, surrounded by either single quote (`'') or double quote (`"') characters (only the single quote if you run in ANSI mode). Examples:
'a string' "another string"
Within a string, certain sequences have special meaning. Each of these sequences begins with a backslash (`\'), known as the escape character. MySQL recognises the following escape sequences:
\0
NUL)
character.
\'
\"
\b
\n
\r
\t
\z
mysql database <
filename.)
\\
\%
\_
Note that if you use `\%' or `\_' in some string contexts, these will return the strings `\%' and `\_' and not `%' and `_'.
There are several ways to include quotes within a string:
The SELECT statements shown below demonstrate how quoting and
escaping work:
mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello'; +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello"; +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "This\nIs\nFour\nlines"; +--------------------+ | This Is Four lines | +--------------------+
If you want to insert binary data into a BLOB column, the
following characters must be represented by escape sequences:
NUL
\
'
"
If you write C code, you can use the C API function
mysql_escape_string() to escape characters for the
INSERT statement. See section 8.4.2
C API Function Overview. In Perl, you can use the quote method
of the DBI package to convert special characters to the proper
escape sequences. See section 8.2.2
The DBI Interface.
You should use an escape function on any string that might contain any of the special characters listed above!
Integers are represented as a sequence of digits. Floats use `.' as a decimal separator. Either type of number may be preceded by `-' to indicate a negative value.
Examples of valid integers:
1221 0 -32
Examples of valid floating-point numbers:
294.42 -32032.6809e+10 148.00
An integer may be used in a floating-point context; it is interpreted as the equivalent floating-point number.
MySQL supports hexadecimal values. In number context these act like an integer (64-bit precision). In string context these act like a binary string where each pair of hex digits is converted to a character:
mysql> SELECT x'FF'
-> 255
mysql> SELECT 0xa+0;
-> 10
mysql> select 0x5061756c;
-> Paul
The x'hexstring' syntax (new in 4.0) is based on ANSI SQL and the 0x syntax
is based on ODBC. Hexadecimal strings are often used by ODBC to give values for
BLOB columns. You can convert a string or a number to hexadecimal with the
HEX() function.
NULL ValuesThe NULL value means ``no data'' and is different from values
such as 0 for numeric types or the empty string for string types.
See section A.5.3
Problems with NULL Values.
NULL may be represented by \N when using the text
file import or export formats (LOAD DATA INFILE, SELECT ...
INTO OUTFILE). See section 6.4.9
LOAD DATA INFILE Syntax.
Database, table, index, column, and alias names all follow the same rules in MySQL.
Note that the rules changed starting with MySQL Version 3.23.6 when we introduced quoting of identifiers (database, table, and column names) with ``'. `"' will also work to quote identifiers if you run in ANSI mode. See section 1.7.2 Running MySQL in ANSI Mode.
| Identifier | Max length | Allowed characters |
| Database | 64 | Any character that is allowed in a directory name except `/' or `.'. |
| Table | 64 | Any character that is allowed in a file name, except `/' or `.'. |
| Column | 64 | All characters. |
| Alias | 255 | All characters. |
Note that in addition to the above, you can't have ASCII(0) or ASCII(255) or the quoting character in an identifier.
Note that if the identifier is a restricted word or contains special
characters you must always quote it with ` when you use it:
SELECT * from `select` where `select`.id > 100;
In previous versions of MySQL, the name rules are as follows:
--default-character-set option to mysqld. See
section 4.6.1
The Character Set Used for Data and Sorting.
It is recommended that you do not use names like 1e, because an
expression like 1e+1 is ambiguous. It may be interpreted as the
expression 1e + 1 or as the number 1e+1.
In MySQL you can refer to a column using any of the following forms:
| Column reference | Meaning |
col_name |
Column col_name from whichever table used in the query
contains a column of that name. |
tbl_name.col_name |
Column col_name from table tbl_name of the
current database. |
db_name.tbl_name.col_name |
Column col_name from table tbl_name of the
database db_name. This form is available in MySQL Version
3.22 or later. |
`column_name` |
A column that is a keyword or contains special characters. |
You need not specify a tbl_name or db_name.tbl_name
prefix for a column reference in a statement unless the reference would be
ambiguous. For example, suppose tables t1 and t2 each
contain a column c, and you retrieve c in a
SELECT statement that uses both t1 and
t2. In this case, c is ambiguous because it is not
unique among the tables used in the statement, so you must indicate which table
you mean by writing t1.c or t2.c. Similarly, if you
are retrieving from a table t in database db1 and from
a table t in database db2, you must refer to columns
in those tables as db1.t.col_name and db2.t.col_name.
The syntax .tbl_name
means the table tbl_name in the current database. This syntax is
accepted for ODBC compatibility, because some ODBC programs prefix table names
with a `.' character.
In MySQL, databases and tables correspond to directories and files within those directories. Consequently, the case sensitivity of the underlying operating system determines the case sensitivity of database and table names. This means database and table names are case sensitive in Unix and case insensitive in Windows. See section 1.7.3 MySQL Extensions to ANSI SQL92.
NOTE: Although database and table names are case insensitive
for Windows, you should not refer to a given database or table using different
cases within the same query. The following query would not work because it
refers to a table both as my_table and as MY_TABLE:
mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1;
Column names are case insensitive in all cases.
Aliases on tables are case sensitive. The following query would not work
because it refers to the alias both as a and as A:
mysql> SELECT col_name FROM tbl_name AS a
WHERE a.col_name = 1 OR A.col_name = 2;
Aliases on columns are case insensitive.
If you have a problem remembering the used cases for a table names, adopt a consistent convention, such as always creating databases and tables using lowercase names.
One way to avoid this problem is to start mysqld with -O
lower_case_table_names=1. By default this option is 1 on Windows and 0 on
Unix.
If lower_case_table_names is 1 MySQL will convert all table
names to lower case on storage and lookup. Note that if you change this option,
you need to first convert your old table names to lower case before starting
mysqld.
MySQL supports thread-specific variables with the @variablename
syntax. A variable name may consist of alphanumeric characters from the current
character set and also `_', `$', and `.'
. The default character set is ISO-8859-1 Latin1; this may be changed with the
--default-character-set option to mysqld. See section
4.6.1
The Character Set Used for Data and Sorting.
Variables don't have to be initialised. They contain NULL by
default and can store an integer, real, or string value. All variables for a
thread are automatically freed when the thread exits.
You can set a variable with the SET syntax:
SET @variable= { integer expression | real expression | string expression }
[,@variable= ...].
You can also set a variable in an expression with the
@variable:=expr syntax:
select @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3; +----------------------+------+------+------+ | @t1:=(@t2:=1)+@t3:=4 | @t1 | @t2 | @t3 | +----------------------+------+------+------+ | 5 | 5 | 1 | 4 | +----------------------+------+------+------+
(We had to use the := syntax here, because = was
reserved for comparisons.)
User variables may be used where expressions are allowed. Note that this does
not currently include use in contexts where a number is explicitly required,
such as in the LIMIT clause of a SELECT statement, or
the IGNORE number LINES clause of a LOAD DATA
statement.
NOTE: In a SELECT statement, each expression is
only evaluated when it's sent to the client. This means that in the
HAVING, GROUP BY, or ORDER BY clause, you
can't refer to an expression that involves variables that are set in the
SELECT part. For example, the following statement will NOT work as
expected:
SELECT (@aa:=id) AS a, (@aa+3) AS b FROM table_name HAVING b=5;
The reason is that @aa will not contain the value of the current
row, but the value of id for the previous accepted row.
The MySQL server supports the # to end of line, -- to end
of line and /* in-line or multiple-line */ comment styles:
mysql> select 1+1; # This comment continues to the end of line mysql> select 1+1; -- This comment continues to the end of line mysql> select 1 /* this is an in-line comment */ + 1; mysql> select 1+ /* this is a multiple-line comment */ 1;
Note that the -- comment style requires you to have at least one
space after the --!
Although the server understands the comment syntax just described, there are
some limitations on the way that the mysql client parses /*
... */ comments:
mysql interactively, you
can tell that it has gotten confused like this because the prompt changes from
mysql> to '> or ">.
These limitations apply both when you run mysql interactively
and when you put commands in a file and tell mysql to read its
input from that file with mysql < some-file.
MySQL only supports the `--' ANSI SQL comment style if it is followed by a space. See section 1.7.4.7 `--' as the Start of a Comment.
A common problem stems from trying to create a table with column names that
use the names of datatypes or functions built into MySQL, such as
TIMESTAMP or GROUP. You're allowed to do it (for
example, ABS is an allowed column name), but whitespace is not
allowed between a function name and the `(' when using functions
whose names are also column names.
The following words are explicitly reserved in MySQL. Most of them are
forbidden by ANSI SQL92 as column and/or table names (for example,
group). A few are reserved because MySQL needs them and is
(currently) using a yacc parser:
| Word | Word | Word | Word |
ADD |
ALL |
ALTER |
ANALYZE |
AND |
AS |
ASC |
AUTO_INCREMENT |
BDB |
BERKELEYDB |
BETWEEN |
BIGINT |
BINARY |
BLOB |
BOTH |
BY |
CASCADE |
CASE |
CHANGE |
CHAR |
CHARACTER |
COLUMN |
COLUMNS |
CONSTRAINT |
CREATE |
CROSS |
CURRENT_DATE |
CURRENT_TIME |
CURRENT_TIMESTAMP |
DATABASE |
DATABASES |
DAY_HOUR |
DAY_MINUTE |
DAY_SECOND |
DEC |
DECIMAL |
DEFAULT |
DELAYED |
DELETE |
DESC |
DESCRIBE |
DISTINCT |
DISTINCTROW |
DOUBLE |
DROP |
ELSE |
ENCLOSED |
ESCAPED |
EXISTS |
EXPLAIN |
FIELDS |
FLOAT |
FOR |
FOREIGN |
FROM |
FULLTEXT |
FUNCTION |
GRANT |
GROUP |
HAVING |
HIGH_PRIORITY |
HOUR_MINUTE |
HOUR_SECOND |
IF |
IGNORE |
IN |
INDEX |
INFILE |
INNER |
INNODB |
INSERT |
INSERT_ID |
INT |
INTEGER |
INTERVAL |
INTO |
IS |
JOIN |
KEY |
KEYS |
KILL |
LAST_INSERT_ID |
LEADING |
LEFT |
LIKE |
LIMIT |
LINES |
LOAD |
LOCK |
LONG |
LONGBLOB |
LONGTEXT |
LOW_PRIORITY |
MASTER_LOG_SEQ |
MASTER_SERVER_ID |
MATCH |
MEDIUMBLOB |
MEDIUMINT |
MEDIUMTEXT |
MIDDLEINT |
MINUTE_SECOND |
MRG_MYISAM |
NATURAL |
NOT |
NULL |
NUMERIC |
ON |
OPTIMIZE |
OPTION |
OPTIONALLY |
OR |
ORDER |
OUTER |
OUTFILE |
PARTIAL |
PRECISION |
PRIMARY |
PRIVILEGES |
PROCEDURE |
PURGE |
READ |
REAL |
REFERENCES |
REGEXP |
RENAME |
REPLACE |
REQUIRE |
RESTRICT |
RETURNS |
REVOKE |
RIGHT |
RLIKE |
SELECT |
SET |
SHOW |
SMALLINT |
SONAME |
SQL_AUTO_IS_NULL |
SQL_BIG_RESULT |
SQL_BIG_SELECTS |
SQL_BIG_TABLES |
SQL_BUFFER_RESULT |
SQL_CALC_FOUND_ROWS |
SQL_LOG_BIN |
SQL_LOG_OFF |
SQL_LOG_UPDATE |
SQL_LOW_PRIORITY_UPDATES |
SQL_MAX_JOIN_SIZE |
SQL_QUOTE_SHOW_CREATE |
SQL_SAFE_UPDATES |
SQL_SELECT_LIMIT |
SQL_SLAVE_SKIP_COUNTER |
SQL_SMALL_RESULT |
SQL_WARNINGS |
SSL |
STARTING |
STRAIGHT_JOIN |
STRIPED |
TABLE |
TABLES |
TERMINATED |
THEN |
TINYBLOB |
TINYINT |
TINYTEXT |
TO |
TRAILING |
UNION |
UNIQUE |
UNLOCK |
UNSIGNED |
UPDATE |
USAGE |
USE |
USING |
VALUES |
VARBINARY |
VARCHAR |
VARYING |
WHEN |
WHERE |
WITH |
WRITE |
YEAR_MONTH |
ZEROFILL |
The following symbols (from the table above) are disallowed by ANSI SQL but allowed by MySQL as column/table names. This is because some of these names are very natural names and a lot of people have already used them.
ACTION
BIT
DATE
ENUM
NO
TEXT
TIME
TIMESTAMP MySQL supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available and summarises the storage requirements for each column type, then provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values.
The column types supported by MySQL are listed below. The following code letters are used in the descriptions:
M
D
M-2. Square brackets (`[' and `]') indicate parts of type specifiers that are optional.
Note that if you specify ZEROFILL for a column, MySQL will
automatically add the UNSIGNED attribute to the column.
TINYINT[(M)] [UNSIGNED] [ZEROFILL]
-128 to 127. The unsigned range is 0 to
255.
SMALLINT[(M)] [UNSIGNED] [ZEROFILL]
-32768 to
32767. The unsigned range is 0 to
65535.
MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]
-8388608 to
8388607. The unsigned range is 0 to
16777215.
INT[(M)] [UNSIGNED] [ZEROFILL]
-2147483648 to
2147483647. The unsigned range is 0 to
4294967295.
INTEGER[(M)] [UNSIGNED] [ZEROFILL]
INT.
BIGINT[(M)] [UNSIGNED] [ZEROFILL]
-9223372036854775808 to
9223372036854775807. The unsigned range is 0 to
18446744073709551615. Some things you should be aware about
BIGINT columns:
BIGINT or DOUBLE values, so you shouldn't use
unsigned big integers larger than 9223372036854775807 (63 bits)
except with bit functions! If you do that, some of the last digits in the
result may be wrong because of rounding errors when converting the
BIGINT to a DOUBLE. MySQL 4.0 can handle
BIGINT in the following cases:
BIGINT
column.
MIN(big_int_column) and
MAX(big_int_column).
+, -, *
etc) where both operands are integers. BIGINT
column by storing it as a string, as there is in this case there will be no
intermediate double representation.
BIGINT arithmetic when both arguments are INTEGER
values! This means that if you multiply two big integers (or results from
functions that return integers) you may get unexpected results when the
result is larger than 9223372036854775807. FLOAT(precision) [ZEROFILL]
precision can be
<=24 for a single-precision floating-point number and between
25 and 53 for a double-precision floating-point number. These types are like
the FLOAT and DOUBLE types described immediately
below. FLOAT(X) has the same range as the corresponding
FLOAT and DOUBLE types, but the display size and
number of decimals is undefined. In MySQL Version 3.23, this is a true
floating-point value. In earlier MySQL versions, FLOAT(precision)
always has 2 decimals. Note that using FLOAT may give you some
unexpected problems as all calculation in MySQL is done with double precision.
See section A.5.6
Solving Problems with No Matching Rows. This syntax is provided for ODBC compatibility.
FLOAT[(M,D)] [ZEROFILL]
-3.402823466E+38 to
-1.175494351E-38, 0, and
1.175494351E-38 to 3.402823466E+38. The M is the
display width and D is the number of decimals. FLOAT without an
argument or with an argument of <= 24 stands for a single-precision
floating-point number.
DOUBLE[(M,D)] [ZEROFILL]
-1.7976931348623157E+308 to
-2.2250738585072014E-308, 0, and
2.2250738585072014E-308 to 1.7976931348623157E+308.
The M is the display width and D is the number of decimals.
DOUBLE without an argument or FLOAT(X) where 25
<= X <= 53 stands for a double-precision floating-point number.
DOUBLE PRECISION[(M,D)] [ZEROFILL]
REAL[(M,D)] [ZEROFILL]
DOUBLE.
DECIMAL[(M[,D])] [ZEROFILL]
CHAR column: ``unpacked'' means the number is stored as a string,
using one character for each digit of the value. The decimal point and, for
negative numbers, the `-' sign, are not counted in M (but space
for these are reserved). If D is 0, values will have no decimal
point or fractional part. The maximum range of DECIMAL values is
the same as for DOUBLE, but the actual range for a given
DECIMAL column may be constrained by the choice of M
and D. If D is left out it's set to 0. If
M is left out it's set to 10. Note that in MySQL Version 3.22 the
M argument had to includes the space needed for the sign and the
decimal point.
NUMERIC(M,D) [ZEROFILL]
DECIMAL.
DATE
'1000-01-01' to
'9999-12-31'. MySQL displays DATE values in
'YYYY-MM-DD' format, but allows you to assign values to
DATE columns using either strings or numbers. See section 6.2.2.2
The DATETIME, DATE, and TIMESTAMP
Types.
DATETIME
'1000-01-01
00:00:00' to '9999-12-31 23:59:59'. MySQL displays
DATETIME values in 'YYYY-MM-DD HH:MM:SS' format, but
allows you to assign values to DATETIME columns using either
strings or numbers. See section 6.2.2.2
The DATETIME, DATE, and TIMESTAMP
Types.
TIMESTAMP[(M)]
'1970-01-01 00:00:00' to sometime
in the year 2037. MySQL displays TIMESTAMP values in
YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD,
or YYMMDD format, depending on whether M is
14 (or missing), 12, 8, or
6, but allows you to assign values to TIMESTAMP
columns using either strings or numbers. A TIMESTAMP column is
useful for recording the date and time of an INSERT or
UPDATE operation because it is automatically set to the date and
time of the most recent operation if you don't give it a value yourself. You
can also set it to the current date and time by assigning it a
NULL value. See section 6.2.2
Date and Time Types. A TIMESTAMP is always stored in 4 bytes.
The M argument only affects how the TIMESTAMP column
is displayed. Note that TIMESTAMP(X) columns where X is 8 or 14
are reported to be numbers while other TIMESTAMP(X) columns are
reported to be strings. This is just to ensure that one can reliably dump and
restore the table with these types! See section 6.2.2.2
The DATETIME, DATE, and TIMESTAMP
Types.
TIME
'-838:59:59' to
'838:59:59'. MySQL displays TIME values in
'HH:MM:SS' format, but allows you to assign values to
TIME columns using either strings or numbers. See section 6.2.2.3 The
TIME Type.
YEAR[(2|4)]
1901 to 2155, 0000 in the 4-digit
year format, and 1970-2069 if you use the 2-digit format (70-69). MySQL
displays YEAR values in YYYY format, but allows you
to assign values to YEAR columns using either strings or numbers.
(The YEAR type is new in MySQL Version 3.22.) See section 6.2.2.4 The
YEAR Type.
[NATIONAL] CHAR(M) [BINARY]
M is 1 to 255
characters. Trailing spaces are removed when the value is retrieved.
CHAR values are sorted and compared in case-insensitive fashion
according to the default character set unless the BINARY keyword
is given. NATIONAL CHAR (short form NCHAR) is the
ANSI SQL way to define that a CHAR column should use the default CHARACTER
set. This is the default in MySQL. CHAR is a shorthand for
CHARACTER. MySQL allows you to create a column of type
CHAR(0). This is mainly useful when you have to be compliant with
some old applications that depend on the existence of a column but that do not
actually use the value. This is also quite nice when you need a column that
only can take 2 values: A CHAR(0), that is not defined as
NOT NULL, will only occupy one bit and can only take 2 values:
NULL or "". See section 6.2.3.1 The
CHAR and VARCHAR Types.
BIT
BOOL
CHAR
CHAR(1).
[NATIONAL] VARCHAR(M) [BINARY]
M is 1 to 255 characters.
VARCHAR values are sorted and compared in case-insensitive
fashion unless the BINARY keyword is given. See section 6.5.3.1
Silent Column Specification Changes. VARCHAR is a shorthand
for CHARACTER VARYING. See section 6.2.3.1 The
CHAR and VARCHAR Types.
TINYBLOB
TINYTEXT
BLOB or TEXT column with a maximum length of
255 (2^8 - 1) characters. See section 6.5.3.1
Silent Column Specification Changes. See section 6.2.3.2 The
BLOB and TEXT Types.
BLOB
TEXT
BLOB or TEXT column with a maximum length of
65535 (2^16 - 1) characters. See section 6.5.3.1
Silent Column Specification Changes. See section 6.2.3.2 The
BLOB and TEXT Types.
MEDIUMBLOB
MEDIUMTEXT
BLOB or TEXT column with a maximum length of
16777215 (2^24 - 1) characters. See section 6.5.3.1
Silent Column Specification Changes. See section 6.2.3.2 The
BLOB and TEXT Types.
LONGBLOB
LONGTEXT
BLOB or TEXT column with a maximum length of
4294967295 (2^32 - 1) characters. See section 6.5.3.1
Silent Column Specification Changes. Note that because the server/client
protocol and MyISAM tables has currently a limit of 16M per communication
packet / table row, you can't yet use this the whole range of this type. See
section 6.2.3.2 The
BLOB and TEXT Types.
ENUM('value1','value2',...)
'value1', 'value2',
..., NULL or the special "" error
value. An ENUM can have a maximum of 65535 distinct values. See
section 6.2.3.3 The
ENUM Type.
SET('value1','value2',...)
'value1',
'value2', ... A SET can have a maximum
of 64 members. See section 6.2.3.4 The
SET Type. MySQL supports all of the ANSI/ISO SQL92 numeric types. These types include
the exact numeric data types (NUMERIC, DECIMAL,
INTEGER, and SMALLINT), as well as the approximate
numeric data types (FLOAT, REAL, and DOUBLE
PRECISION). The keyword INT is a synonym for
INTEGER, and the keyword DEC is a synonym for
DECIMAL.
The NUMERIC and DECIMAL types are implemented as
the same type by MySQL, as permitted by the SQL92 standard. They are used for
values for which it is important to preserve exact precision, for example with
monetary data. When declaring a column of one of these types the precision and
scale can be (and usually is) specified; for example:
salary DECIMAL(9,2)
In this example, 9 (precision) represents the
number of significant decimal digits that will be stored for values, and
2 (scale) represents the number of digits that will be
stored following the decimal point. In this case, therefore, the range of values
that can be stored in the salary column is from
-9999999.99 to 9999999.99. (MySQL can actually store
numbers up to 9999999.99 in this column because it doesn't have to
store the sign for positive numbers)
In ANSI/ISO SQL92, the syntax DECIMAL(p) is equivalent to
DECIMAL(p,0). Similarly, the syntax DECIMAL is
equivalent to DECIMAL(p,0), where the implementation is allowed to
decide the value of p. MySQL does not currently support either of
these variant forms of the DECIMAL/NUMERIC data types.
This is not generally a serious problem, as the principal benefits of these
types derive from the ability to control both precision and scale explicitly.
DECIMAL and NUMERIC values are stored as strings,
rather than as binary floating-point numbers, in order to preserve the decimal
precision of those values. One character is used for each digit of the value,
the decimal point (if scale > 0), and the `-' sign
(for negative numbers). If scale is 0, DECIMAL and
NUMERIC values contain no decimal point or fractional part.
The maximum range of DECIMAL and NUMERIC values is
the same as for DOUBLE, but the actual range for a given
DECIMAL or NUMERIC column can be constrained by the
precision or scale for a given column. When such a
column is assigned a value with more digits following the decimal point than are
allowed by the specified scale, the value is rounded to that
scale. When a DECIMAL or NUMERIC column
is assigned a value whose magnitude exceeds the range implied by the specified
(or defaulted) precision and scale, MySQL stores the
value representing the corresponding end point of that range.
As an extension to the ANSI/ISO SQL92 standard, MySQL also supports the
integral types TINYINT, MEDIUMINT, and
BIGINT as listed in the tables above. Another extension is
supported by MySQL for optionally specifying the display width of an integral
value in parentheses following the base keyword for the type (for example,
INT(4)). This optional width specification is used to left-pad the
display of values whose width is less than the width specified for the column,
but does not constrain the range of values that can be stored in the column, nor
the number of digits that will be displayed for values whose width exceeds that
specified for the column. When used in conjunction with the optional extension
attribute ZEROFILL, the default padding of spaces is replaced with
zeroes. For example, for a column declared as INT(5) ZEROFILL, a
value of 4 is retrieved as 00004. Note that if you
store larger values than the display width in an integer column, you may
experience problems when MySQL generates temporary tables for some complicated
joins, as in these cases MySQL trusts that the data did fit into the original
column width.
All integral types can have an optional (non-standard) attribute
UNSIGNED. Unsigned values can be used when you want to allow only
positive numbers in a column and you need a little bigger numeric range for the
column.
The FLOAT type is used to represent approximate numeric data
types. The ANSI/ISO SQL92 standard allows an optional specification of the
precision (but not the range of the exponent) in bits following the keyword
FLOAT in parentheses. The MySQL implementation also supports this
optional precision specification. When the keyword FLOAT is used
for a column type without a precision specification, MySQL uses four bytes to
store the values. A variant syntax is also supported, with two numbers given in
parentheses following the FLOAT keyword. With this option, the
first number continues to represent the storage requirements for the value in
bytes, and the second number specifies the number of digits to be stored and
displayed following the decimal point (as with DECIMAL and
NUMERIC). When MySQL is asked to store a number for such a column
with more decimal digits following the decimal point than specified for the
column, the value is rounded to eliminate the extra digits when the value is
stored.
The REAL and DOUBLE PRECISION types do not accept
precision specifications. As an extension to the ANSI/ISO SQL92 standard, MySQL
recognises DOUBLE as a synonym for the DOUBLE
PRECISION type. In contrast with the standard's requirement that the
precision for REAL be smaller than that used for DOUBLE
PRECISION, MySQL implements both as 8-byte double-precision
floating-point values (when not running in ``ANSI mode''). For maximum
portability, code requiring storage of approximate numeric data values should
use FLOAT or DOUBLE PRECISION with no specification of
precision or number of decimal points.
When asked to store a value in a numeric column that is outside the column type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.
For example, the range of an INT column is
-2147483648 to 2147483647. If you try to insert
-9999999999 into an INT column, the value is clipped
to the lower endpoint of the range, and -2147483648 is stored
instead. Similarly, if you try to insert 9999999999,
2147483647 is stored instead.
If the INT column is UNSIGNED, the size of the
column's range is the same but its endpoints shift up to 0 and
4294967295. If you try to store -9999999999 and
9999999999, the values stored in the column become 0
and 4294967296.
Conversions that occur due to clipping are reported as ``warnings'' for
ALTER TABLE, LOAD DATA INFILE, UPDATE,
and multi-row INSERT statements.
The date and time types are DATETIME, DATE,
TIMESTAMP, TIME, and YEAR. Each of these
has a range of legal values, as well as a ``zero'' value that is used when you
specify a really illegal value. Note that MySQL allows you to store certain 'not
strictly' legal date values, for example 1999-11-31. The reason for
this is that we think it's the responsibility of the application to handle date
checking, not the SQL servers. To make the date checking 'fast', MySQL only
checks that the month is in the range of 0-12 and the day is in the range of
0-31. The above ranges are defined this way because MySQL allows you to store,
in a DATE or DATETIME column, dates where the day or
month-day is zero. This is extremely useful for applications that need to store
a birth-date for which you don't know the exact date. In this case you simply
store the date like 1999-00-00 or 1999-01-00. (You
cannot expect to get a correct value from functions like DATE_SUB()
or DATE_ADD for dates like these.)
Here are some general considerations to keep in mind when working with date and time types:
'98-09-04'), rather than in
the month-day-year or day-month-year orders commonly used elsewhere (for
example, '09-04-98', '04-09-98').
TIME values are clipped to the appropriate endpoint
of the TIME range.) The table below shows the format of the
``zero'' value for each type:
| Column type | ``Zero'' value |
DATETIME |
'0000-00-00 00:00:00' |
DATE |
'0000-00-00' |
TIMESTAMP |
00000000000000 (length depends on display size) |
TIME |
'00:00:00' |
YEAR |
0000 |
'0' or 0, which are easier to write.
NULL in MyODBC
Version 2.50.12 and above, because ODBC can't handle such values. MySQL itself is Y2K-safe (see section 1.2.5 Year 2000 Compliance), but input values presented to MySQL may not be. Any input containing 2-digit year values is ambiguous, because the century is unknown. Such values must be interpreted into 4-digit form because MySQL stores years internally using four digits.
For DATETIME, DATE, TIMESTAMP, and
YEAR types, MySQL interprets dates with ambiguous year values using
the following rules:
00-69 are converted to
2000-2069.
70-99 are converted to
1970-1999. Remember that these rules provide only reasonable guesses as to what your data mean. If the heuristics used by MySQL don't produce the correct values, you should provide unambiguous input containing 4-digit year values.
ORDER BY will sort 2-digit YEAR/DATE/DATETIME types
properly.
Note also that some functions like MIN() and MAX()
will convert a TIMESTAMP/DATE to a number. This means that a
timestamp with a 2-digit year will not work properly with these functions. The
fix in this case is to convert the TIMESTAMP/DATE to 4-digit year
format or use something like MIN(DATE_ADD(timestamp,INTERVAL 0
DAYS)).
DATETIME, DATE, and
TIMESTAMP TypesThe DATETIME, DATE, and TIMESTAMP
types are related. This section describes their characteristics, how they are
similar, and how they differ.
The DATETIME type is used when you need values that contain both
date and time information. MySQL retrieves and displays DATETIME
values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is
'1000-01-01 00:00:00' to '9999-12-31 23:59:59'.
(``Supported'' means that although earlier values might work, there is no
guarantee that they will.)
The DATE type is used when you need only a date value, without a
time part. MySQL retrieves and displays DATE values in
'YYYY-MM-DD' format. The supported range is
'1000-01-01' to '9999-12-31'.
The TIMESTAMP column type provides a type that you can use to
automatically mark INSERT or UPDATE operations with
the current date and time. If you have multiple TIMESTAMP columns,
only the first one is updated automatically.
Automatic updating of the first TIMESTAMP column occurs under
any of the following conditions:
INSERT or
LOAD DATA INFILE statement.
UPDATE statement
and some other column changes value. (Note that an UPDATE that
sets a column to the value it already has will not cause the
TIMESTAMP column to be updated, because if you set a column to
its current value, MySQL ignores the update for efficiency.)
TIMESTAMP column to NULL.
TIMESTAMP columns other than the first may also be set to the
current date and time. Just set the column to NULL or to
NOW().
You can set any TIMESTAMP column to a value different than the
current date and time by setting it explicitly to the desired value. This is
true even for the first TIMESTAMP column. You can use this property
if, for example, you want a TIMESTAMP to be set to the current date
and time when you create a row, but not to be changed whenever the row is
updated later:
TIMESTAMP column explicitly to its current value. On the other hand, you may find it just as easy to use a
DATETIME column that you initialise to NOW() when the
row is created and leave alone for subsequent updates.
TIMESTAMP values may range from the beginning of 1970 to
sometime in the year 2037, with a resolution of one second. Values are displayed
as numbers.
The format in which MySQL retrieves and displays TIMESTAMP
values depends on the display size, as illustrated by the table below. The
`full' TIMESTAMP format is 14 digits, but TIMESTAMP
columns may be created with shorter display sizes:
| Column type | Display format |
TIMESTAMP(14) |
YYYYMMDDHHMMSS |
TIMESTAMP(12) |
YYMMDDHHMMSS |
TIMESTAMP(10) |
YYMMDDHHMM |
TIMESTAMP(8) |
YYYYMMDD |
TIMESTAMP(6) |
YYMMDD |
TIMESTAMP(4) |
YYMM |
TIMESTAMP(2) |
YY |
All TIMESTAMP columns have the same storage size, regardless of
display size. The most common display sizes are 6, 8, 12, and 14. You can
specify an arbitrary display size at table creation time, but values of 0 or
greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to 13
are coerced to the next higher even number.
You can specify DATETIME, DATE, and
TIMESTAMP values using any of a common set of formats:
'YYYY-MM-DD HH:MM:SS' or
'YY-MM-DD HH:MM:SS' format. A ``relaxed'' syntax is allowed--any
punctuation character may be used as the delimiter between date parts or time
parts. For example, '98-12-31 11:30:45', '98.12.31
11+30+45', '98/12/31 11*30*45', and '98@12@31
11^30^45' are equivalent.
'YYYY-MM-DD' or 'YY-MM-DD'
format. A ``relaxed'' syntax is allowed here, too. For example,
'98-12-31', '98.12.31', '98/12/31', and
'98@12@31' are equivalent.
'YYYYMMDDHHMMSS' or
'YYMMDDHHMMSS' format, provided that the string makes sense as a
date. For example, '19970523091528' and
'970523091528' are interpreted as '1997-05-23
09:15:28', but '971122129015' is illegal (it has a
nonsensical minute part) and becomes '0000-00-00 00:00:00'.
'YYYYMMDD' or
'YYMMDD' format, provided that the string makes sense as a date.
For example, '19970523' and '970523' are interpreted
as '1997-05-23', but '971332' is illegal (it has
nonsensical month and day parts) and becomes '0000-00-00'.
YYYYMMDDHHMMSS or
YYMMDDHHMMSS format, provided that the number makes sense as a
date. For example, 19830905132800 and 830905132800
are interpreted as '1983-09-05 13:28:00'.
YYYYMMDD or YYMMDD format,
provided that the number makes sense as a date. For example,
19830905 and 830905 are interpreted as
'1983-09-05'.
DATETIME, DATE, or TIMESTAMP context,
such as NOW() or CURRENT_DATE. Illegal DATETIME, DATE, or TIMESTAMP
values are converted to the ``zero'' value of the appropriate type
('0000-00-00 00:00:00', '0000-00-00', or
00000000000000).
For values specified as strings that include date part delimiters, it is not
necessary to specify two digits for month or day values that are less than
10. '1979-6-9' is the same as
'1979-06-09'. Similarly, for values specified as strings that
include time part delimiters, it is not necessary to specify two digits for
hour, month, or second values that are less than 10.
'1979-10-30 1:2:3' is the same as '1979-10-30
01:02:03'.
Values specified as numbers should be 6, 8, 12, or 14 digits long. If the
number is 8 or 14 digits long, it is assumed to be in YYYYMMDD or
YYYYMMDDHHMMSS format and that the year is given by the first 4
digits. If the number is 6 or 12 digits long, it is assumed to be in
YYMMDD or YYMMDDHHMMSS format and that the year is
given by the first 2 digits. Numbers that are not one of these lengths are
interpreted as though padded with leading zeros to the closest length.
Values specified as non-delimited
strings are interpreted using their length as given. If the string is 8 or 14
characters long, the year is assumed to be given by the first 4 characters.
Otherwise the year is assumed to be given by the first 2 characters. The string
is interpreted from left to right to find year, month, day, hour, minute, and
second values, for as many parts as are present in the string. This means you
should not use strings that have fewer than 6 characters. For example, if you
specify '9903', thinking that will represent March, 1999, you will
find that MySQL inserts a ``zero'' date into your table. This is because the
year and month values are 99 and 03, but the day part
is missing (zero), so the value is not a legal date.
TIMESTAMP columns store legal values using the full precision
with which the value was specified, regardless of the display size. This has
several implications:
TIMESTAMP(4) or TIMESTAMP(2). Otherwise, the value
will not be a legal date and 0 will be stored.
ALTER TABLE to widen a narrow
TIMESTAMP column, information will be displayed that previously
was ``hidden''.
TIMESTAMP column does not cause
information to be lost, except in the sense that less information is shown
when the values are displayed.
TIMESTAMP values are stored to full precision, the
only function that operates directly on the underlying stored value is
UNIX_TIMESTAMP(). Other functions operate on the formatted
retrieved value. This means you cannot use functions such as
HOUR() or SECOND() unless the relevant part of the
TIMESTAMP value is included in the formatted value. For example,
the HH part of a TIMESTAMP column is not displayed
unless the display size is at least 10, so trying to use HOUR()
on shorter TIMESTAMP values produces a meaningless result.
You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information:
DATE value to a DATETIME or
TIMESTAMP object, the time part of the resulting value is set to
'00:00:00', because the DATE value contains no time
information.
DATETIME or TIMESTAMP value to a
DATE object, the time part of the resulting value is deleted,
because the DATE type stores no time information.
DATETIME, DATE, and
TIMESTAMP values all can be specified using the same set of
formats, the types do not all have the same range of values. For example,
TIMESTAMP values cannot be earlier than 1970 or
later than 2037. This means that a date such as
'1968-01-01', while legal as a DATETIME or
DATE value, is not a valid TIMESTAMP value and will
be converted to 0 if assigned to such an object. Be aware of certain pitfalls when specifying date values:
'10:11:12' might look
like a time value because of the `:' delimiter, but if used in a
date context will be interpreted as the year '2010-11-12'. The
value '10:45:15' will be converted to '0000-00-00'
because '45' is not a legal month.
00-69 are converted to
2000-2069.
70-99 are converted to
1970-1999. TIME TypeMySQL retrieves and displays TIME values in
'HH:MM:SS' format (or 'HHH:MM:SS' format for large
hours values). TIME values may range from '-838:59:59'
to '838:59:59'. The reason the hours part may be so large is that
the TIME type may be used not only to represent a time of day
(which must be less than 24 hours), but also elapsed time or a time interval
between two events (which may be much greater than 24 hours, or even negative).
You can specify TIME values in a variety of formats:
'D HH:MM:SS.fraction' format. (Note that MySQL
doesn't yet store the fraction for the time column.) One can also use one of
the following ``relaxed'' syntax: HH:MM:SS.fraction,
HH:MM:SS, HH:MM, D HH:MM:SS, D
HH:MM, D HH or SS. Here D is
days between 0-33.
'HHMMSS' format, provided
that it makes sense as a time. For example, '101112' is
understood as '10:11:12', but '109712' is illegal
(it has a nonsensical minute part) and becomes '00:00:00'.
HHMMSS format, provided that it makes sense as
a time. For example, 101112 is understood as
'10:11:12'. The following alternative formats are also
understood: SS, MMSS,HHMMSS,
HHMMSS.fraction. Note that MySQL doesn't yet store the fraction
part.
TIME context, such as CURRENT_TIME. For TIME values specified as strings that include a time part
delimiter, it is not necessary to specify two digits for hours, minutes, or
seconds values that are less than 10. '8:3:2' is the
same as '08:03:02'.
Be careful about assigning ``short'' TIME values to a
TIME column. Without semicolon, MySQL interprets values using the
assumption that the rightmost digits represent seconds. (MySQL interprets
TIME values as elapsed time rather than as time of day.) For
example, you might think of '1112' and 1112 as meaning
'11:12:00' (12 minutes after 11 o'clock), but MySQL interprets them
as '00:11:12' (11 minutes, 12 seconds). Similarly,
'12' and 12 are interpreted as
'00:00:12'. TIME values with semicolon, instead, are
always treated as time of the day. That is '11:12' will mean
'11:12:00', not '00:11:12'.
Values that lie outside the TIME range but are otherwise legal
are clipped to the appropriate endpoint of the range. For example,
'-850:00:00' and '850:00:00' are converted to
'-838:59:59' and '838:59:59'.
Illegal TIME values are converted to '00:00:00'.
Note that because '00:00:00' is itself a legal TIME
value, there is no way to tell, from a value of '00:00:00' stored
in a table, whether the original value was specified as '00:00:00'
or whether it was illegal.
YEAR TypeThe YEAR type is a 1-byte type used for representing years.
MySQL retrieves and displays YEAR values in YYYY
format. The range is 1901 to 2155.
You can specify YEAR values in a variety of formats:
'1901' to
'2155'.
1901 to
2155.
'00' to '99'.
Values in the ranges '00' to '69' and
'70' to '99' are converted to YEAR
values in the ranges 2000 to 2069 and
1970 to 1999.
1 to 99.
Values in the ranges 1 to 69 and 70 to
99 are converted to YEAR values in the ranges
2001 to 2069 and 1970 to
1999. Note that the range for two-digit numbers is slightly
different than the range for two-digit strings, because you cannot specify
zero directly as a number and have it be interpreted as 2000. You
must specify it as a string '0' or '00' or
it will be interpreted as 0000.
YEAR context, such as NOW(). Illegal YEAR values are converted to 0000.
The string types are CHAR, VARCHAR,
BLOB, TEXT, ENUM, and SET.
This section describes how these types work, their storage requirements, and how
to use them in your queries.
CHAR and VARCHAR TypesThe CHAR and VARCHAR types are similar, but differ
in the way they are stored and retrieved.
The length of a CHAR column is fixed to the length that you
declare when you create the table. The length can be any value between 1 and
255. (As of MySQL Version 3.23, the length of CHAR may be 0 to
255.) When CHAR values are stored, they are right-padded with
spaces to the specified length. When CHAR values are retrieved,
trailing spaces are removed.
Values in VARCHAR columns are variable-length strings. You can
declare a VARCHAR column to be any length between 1 and 255, just
as for CHAR columns. However, in contrast to CHAR,
VARCHAR values are stored using only as many characters as are
needed, plus one byte to record the length. Values are not padded; instead,
trailing spaces are removed when values are stored. (This space removal differs
from the ANSI SQL specification.)
If you assign a value to a CHAR or VARCHAR column
that exceeds the column's maximum length, the value is truncated to fit.
The table below illustrates the differences between the two types of columns
by showing the result of storing various string values into CHAR(4)
and VARCHAR(4) columns:
| Value | CHAR(4) |
Storage required | VARCHAR(4) |
Storage required |
'' |
' ' |
4 bytes | '' |
1 byte |
'ab' |
'ab ' |
4 bytes | 'ab' |
3 bytes |
'abcd' |
'abcd' |
4 bytes | 'abcd' |
5 bytes |
'abcdefgh' |
'abcd' |
4 bytes | 'abcd' |
5 bytes |
The values retrieved from the CHAR(4) and
VARCHAR(4) columns will be the same in each case, because trailing
spaces are removed from CHAR columns upon retrieval.
Values in CHAR and VARCHAR columns are sorted and
compared in case-insensitive fashion, unless the BINARY attribute
was specified when the table was created. The BINARY attribute
means that column values are sorted and compared in case-sensitive fashion
according to the ASCII order of the machine where the MySQL server is running.
BINARY doesn't affect how the column is stored or retrieved.
The BINARY attribute is sticky. This means that if a column
marked BINARY is used in an expression, the whole expression is
compared as a BINARY value.
MySQL may silently change the type of a CHAR or
VARCHAR column at table creation time. See section 6.5.3.1
Silent Column Specification Changes.
BLOB and TEXT TypesA BLOB is a binary large object that can hold a variable amount
of data. The four BLOB types TINYBLOB,
BLOB, MEDIUMBLOB, and LONGBLOB differ
only in the maximum length of the values they can hold. See section 6.2.6
Column Type Storage Requirements.
The four TEXT types TINYTEXT, TEXT,
MEDIUMTEXT, and LONGTEXT correspond to the four
BLOB types and have the same maximum lengths and storage
requirements. The only difference between BLOB and
TEXT types is that sorting and comparison is performed in
case-sensitive fashion for BLOB values and case-insensitive fashion
for TEXT values. In other words, a TEXT is a
case-insensitive BLOB.
If you assign a value to a BLOB or TEXT column that
exceeds the column type's maximum length, the value is truncated to fit.
In most respects, you can regard a TEXT column as a
VARCHAR column that can be as big as you like. Similarly, you can
regard a BLOB column as a VARCHAR BINARY column. The
differences are:
BLOB and TEXT columns
with MySQL Version 3.23.2 and newer. Older versions of MySQL did not support
this.
BLOB and
TEXT columns when values are stored, as there is for
VARCHAR columns.
BLOB and TEXT columns cannot have
DEFAULT values. MyODBC defines BLOB values as
LONGVARBINARY and TEXT values as
LONGVARCHAR.
Because BLOB and TEXT values may be extremely long,
you may run up against some constraints when using them:
GROUP BY or ORDER BY on a
BLOB or TEXT column, you must convert the column
value into a fixed-length object. The standard way to do this is with the
SUBSTRING function. For example: mysql> select comment from tbl_name,substring(comment,20) as substr
ORDER BY substr;
If you don't do this, only the first max_sort_length bytes
of the column are used when sorting. The default value of
max_sort_length is 1024; this value can be changed using the
-O option when starting the mysqld server. You can
group on an expression involving BLOB or TEXT values
by specifying the column position or by using an alias: mysql> select id,substring(blob_col,1,100) from tbl_name
GROUP BY 2;
mysql> select id,substring(blob_col,1,100) as b from tbl_name
GROUP BY b;
BLOB or TEXT object is
determined by its type, but the largest value you can actually transmit
between the client and server is determined by the amount of available memory
and the size of the communications buffers. You can change the message buffer
size, but you must do so on both the server and client ends. See section 5.5.2
Tuning Server Parameters. Note that each BLOB or TEXT value is represented
internally by a separately allocated object. This is in contrast to all other
column types, for which storage is allocated once per column when the table is
opened.
ENUM TypeAn ENUM is a string object whose value normally is chosen from a
list of allowed values that are enumerated explicitly in the column
specification at table creation time.
The value may also be the empty string ("") or NULL
under certain circumstances:
ENUM (that is, a
string not present in the list of allowed values), the empty string is
inserted instead as a special error value. This string can be distinguished
from a 'normal' empty string by the fact that this string has the numerical
value 0. More about this later.
ENUM is declared NULL, NULL
is also a legal value for the column, and the default value is
NULL. If an ENUM is declared NOT NULL,
the default value is the first element of the list of allowed values. Each enumeration value has an index:
SELECT statement to find rows into which
invalid ENUM values were assigned: mysql> SELECT * FROM tbl_name WHERE enum_col=0;
NULL value is NULL. For example, a column specified as ENUM("one", "two", "three")
can have any of the values shown below. The index of each value is also shown:
| Value | Index |
NULL |
NULL |
"" |
0 |
"one" |
1 |
"two" |
2 |
"three" |
3 |
An enumeration can have a maximum of 65535 elements.
Lettercase is irrelevant when you assign values to an ENUM
column. However, values retrieved from the column later have lettercase matching
the values that were used to specify the allowable values at table creation
time.
If you retrieve an ENUM in a numeric context, the column value's
index is returned. For example, you can retrieve numeric values from an
ENUM column like this:
mysql> SELECT enum_col+0 FROM tbl_name;
If you store a number into an ENUM, the number is treated as an
index, and the value stored is the enumeration member with that index. (However,
this will not work with LOAD DATA, which treats all input as
strings.)
ENUM values are sorted according to the order in which the
enumeration members were listed in the column specification. (In other words,
ENUM values are sorted according to their index numbers.) For
example, "a" sorts before "b" for ENUM("a",
"b"), but "b" sorts before "a" for
ENUM("b", "a"). The empty string sorts before non-empty strings,
and NULL values sort before all other enumeration values.
If you want to get all possible values for an ENUM column, you
should use: SHOW COLUMNS FROM table_name LIKE enum_column_name and
parse the ENUM definition in the second column.
SET TypeA SET is a string object that can have zero or more values, each
of which must be chosen from a list of allowed values specified when the table
is created. SET column values that consist of multiple set members
are specified with members separated by commas (`,'). A consequence
of this is that SET member values cannot themselves contain commas.
For example, a column specified as SET("one", "two") NOT NULL
can have any of these values:
"" "one" "two" "one,two"
A SET can have a maximum of 64 different members.
MySQL stores SET values numerically, with the low-order bit of
the stored value corresponding to the first set member. If you retrieve a
SET value in a numeric context, the value retrieved has bits set
corresponding to the set members that make up the column value. For example, you
can retrieve numeric values from a SET column like this:
mysql> SELECT set_col+0 FROM tbl_name;
If a number is stored into a SET column, the bits that are set
in the binary representation of the number determine the set members in the
column value. Suppose a column is specified as
SET("a","b","c","d"). Then the members have the following bit
values:
SET member |
Decimal value | Binary value |
a |
1 |
0001 |
b |
2 |
0010 |
c |
4 |
0100 |
d |
8 |
1000 |
If you assign a value of 9 to this column, that is
1001 in binary, so the first and fourth SET value
members "a" and "d" are selected and the resulting
value is "a,d".
For a value containing more than one SET element, it does not
matter what order the elements are listed in when you insert the value. It also
does not matter how many times a given element is listed in the value. When the
value is retrieved later, each element in the value will appear once, with
elements listed according to the order in which they were specified at table
creation time. For example, if a column is specified as
SET("a","b","c","d"), then "a,d", "d,a",
and "d,a,a,d,d" will all appear as "a,d" when
retrieved.
If you set a SET column to an unsupported value, the value will
be ignored.
SET values are sorted numerically. NULL values sort
before non-NULL SET values.
Normally, you perform a SELECT on a SET column
using the LIKE operator or the FIND_IN_SET() function:
mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%';
mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0;
But the following will also work:
mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; mysql> SELECT * FROM tbl_name WHERE set_col & 1;
The first of these statements looks for an exact match. The second looks for values containing the first set member.
If you want to get all possible values for a SET column, you
should use: SHOW COLUMNS FROM table_name LIKE set_column_name and
parse the SET definition in the second column.
For the most efficient use of storage, try to use the most precise type in
all cases. For example, if an integer column will be used for values in the
range between 1 and 99999, MEDIUMINT
UNSIGNED is the best type.
Accurate representation of monetary values is a common problem. In MySQL, you
should use the DECIMAL type. This is stored as a string, so no loss
of accuracy should occur. If accuracy is not too important, the
DOUBLE type may also be good enough.
For high precision, you can always convert to a fixed-point type stored in a
BIGINT. This allows you to do all calculations with integers and
convert results back to floating-point values only when necessary.
To make it easier to use code written for SQL implementations from other vendors, MySQL maps column types as shown in the table below. These mappings make it easier to move table definitions from other database engines to MySQL:
| Other vendor type | MySQL type |
BINARY(NUM) |
CHAR(NUM) BINARY |
CHAR VARYING(NUM) |
VARCHAR(NUM) |
FLOAT4 |
FLOAT |
FLOAT8 |
DOUBLE |
INT1 |
TINYINT |
INT2 |
SMALLINT |
INT3 |
MEDIUMINT |
INT4 |
INT |
INT8 |
BIGINT |
LONG VARBINARY |
MEDIUMBLOB |
LONG VARCHAR |
MEDIUMTEXT |
MIDDLEINT |
MEDIUMINT |
VARBINARY(NUM) |
VARCHAR(NUM) BINARY |
Column type mapping occurs at table creation time. If you create a table with
types used by other vendors and then issue a DESCRIBE tbl_name
statement, MySQL reports the table structure using the equivalent MySQL types.
The storage requirements for each of the column types supported by MySQL are listed below by category.
| Column type | Storage required |
TINYINT |
1 byte |
SMALLINT |
2 bytes |
MEDIUMINT |
3 bytes |
INT |
4 bytes |
INTEGER |
4 bytes |
BIGINT |
8 bytes |
FLOAT(X) |
4 if X <= 24 or 8 if 25 <= X <= 53 |
FLOAT |
4 bytes |
DOUBLE |
8 bytes |
DOUBLE PRECISION |
8 bytes |
REAL |
8 bytes |
DECIMAL(M,D) |
M+2 bytes if D > 0, M+1 bytes if D = 0
(D+2, if M < D) |
NUMERIC(M,D) |
M+2 bytes if D > 0, M+1 bytes if D = 0
(D+2, if M < D) |
| Column type | Storage required |
DATE |
3 bytes |
DATETIME |
8 bytes |
TIMESTAMP |
4 bytes |
TIME |
3 bytes |
YEAR |
1 byte |
| Column type | Storage required |
CHAR(M) |
M bytes, 1 <= M <= 255 |
VARCHAR(M) |
L+1 bytes, where L <= M and 1 <=
M <= 255 |
TINYBLOB, TINYTEXT |
L+1 bytes, where L < 2^8 |
BLOB, TEXT |
L+2 bytes, where L < 2^16 |
MEDIUMBLOB, MEDIUMTEXT |
L+3 bytes, where L < 2^24 |
LONGBLOB, LONGTEXT |
L+4 bytes, where L < 2^32 |
ENUM('value1','value2',...) |
1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) |
SET('value1','value2',...) |
1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) |
VARCHAR and the BLOB and
TEXT types are variable-length types, for which the storage
requirements depend on the actual length of column values (represented by
L in the preceding table), rather than on the type's maximum
possible size. For example, a VARCHAR(10) column can hold a string
with a maximum length of 10 characters. The actual storage required is the
length of the string (L), plus 1 byte to record the length of the
string. For the string 'abcd', L is 4 and the storage
requirement is 5 bytes.
The BLOB and TEXT types require 1, 2, 3, or 4 bytes
to record the length of the column value, depending on the maximum possible
length of the type. See section 6.2.3.2 The
BLOB and TEXT Types.
If a table includes any variable-length column types, the record format will also be variable-length. Note that when a table is created, MySQL may, under certain conditions, change a column from a variable-length type to a fixed-length type, or vice-versa. See section 6.5.3.1 Silent Column Specification Changes.
The size of an ENUM object is determined by
the number of different enumeration values. One byte is used for enumerations
with up to 255 possible values. Two bytes are used for enumerations with up to
65535 values. See section 6.2.3.3 The
ENUM Type.
The size of a SET object is determined by
the number of different set members. If the set size is N, the
object occupies (N+7)/8 bytes, rounded up to 1, 2, 3, 4, or 8
bytes. A SET can have a maximum of 64 members. See section 6.2.3.4 The
SET Type.
SELECT and
WHERE ClausesA select_expression or where_definition in a SQL
statement can consist of any expression using the functions described below.
An expression that contains NULL always produces a
NULL value unless otherwise indicated in the documentation for the
operators and functions involved in the expression.
Note: There must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around arguments are permitted, though.
You can force MySQL to accept spaces after the function name by starting
mysqld with --ansi or using the
CLIENT_IGNORE_SPACE to mysql_connect(), but in this
case all function names will become reserved words. See section 1.7.2
Running MySQL in ANSI Mode.
For the sake of brevity, examples display the output from the
mysql program in abbreviated form. So this:
mysql> select MOD(29,9); 1 rows in set (0.00 sec) +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+
is displayed like this:
mysql> select MOD(29,9);
-> 2
( ... )
Use parenthesis to force the order of evaluation in an expression. For example:
mysql> select 1+2*3;
-> 7
mysql> select (1+2)*3;
-> 9
Comparison operations result in a value of 1 (TRUE),
0 (FALSE), or NULL. These functions work for both
numbers and strings. Strings are automatically converted to numbers and numbers
to strings as needed (as in Perl).
MySQL performs comparisons using the following rules:
NULL, the result of the
comparison is NULL, except for the <=>
operator.
TIMESTAMP or DATETIME column and the other argument
is a constant, the constant is converted to a timestamp before the comparison
is performed. This is done to be more ODBC-friendly.
By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English).
The examples below illustrate conversion of strings to numbers for comparison operations:
mysql> SELECT 1 > '6x';
-> 0
mysql> SELECT 7 > '6x';
-> 1
mysql> SELECT 0 > 'x6';
-> 0
mysql> SELECT 0 = 'x6';
-> 1
=
mysql> select 1 = 0;
-> 0
mysql> select '0' = 0;
-> 1
mysql> select '0.0' = 0;
-> 1
mysql> select '0.01' = 0;
-> 0
mysql> select '.01' = 0.01;
-> 1
<>
!=
mysql> select '.01' <> '0.01';
-> 1
mysql> select .01 <> '0.01';
-> 0
mysql> select 'zapp' <> 'zappp';
-> 1
<=
mysql> select 0.1 <= 2;
-> 1
<
mysql> select 2 < 2;
-> 0
>=
mysql> select 2 >= 2;
-> 1
>
mysql> select 2 > 2;
-> 0
<=>
mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1 1 0
IS NULL
IS NOT NULL
NULL: mysql> select 1 IS NULL, 0 IS NULL, NULL IS NULL;
-> 0 0 1
mysql> select 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
-> 1 1 0
expr BETWEEN min AND max
expr is greater than or equal to min and
expr is less than or equal to max,
BETWEEN returns 1, otherwise it returns
0. This is equivalent to the expression (min <= expr AND
expr <= max) if all the arguments are of the same type. The first
argument (expr) determines how the comparison is performed as
follows:
expr is a TIMESTAMP, DATE, or
DATETIME column, MIN() and MAX() are
formatted to the same format if they are constants.
expr is a case-insensitive string expression, a
case-insensitive string comparison is done.
expr is a case-sensitive string expression, a
case-sensitive string comparison is done.
expr is an integer expression, an integer comparison is
done.
mysql> select 1 BETWEEN 2 AND 3;
-> 0
mysql> select 'b' BETWEEN 'a' AND 'c';
-> 1
mysql> select 2 BETWEEN 2 AND '3';
-> 1
mysql> select 2 BETWEEN 2 AND 'x-3';
-> 0
expr IN (value,...)
1 if expr is any of the values in the
IN list, else returns 0. If all values are
constants, then all values are evaluated according to the type of
expr and sorted. The search for the item is then done using a
binary search. This means IN is very quick if the IN
value list consists entirely of constants. If expr is a
case-sensitive string expression, the string comparison is performed in
case-sensitive fashion: mysql> select 2 IN (0,3,5,'wefwf');
-> 0
mysql> select 'wefwf' IN (0,3,5,'wefwf');
-> 1
expr NOT IN (value,...)
NOT (expr IN (value,...)).
ISNULL(expr)
expr is NULL, ISNULL() returns
1, otherwise it returns 0: mysql> select ISNULL(1+1);
-> 0
mysql> select ISNULL(1/0);
-> 1
Note that a comparison of NULL values using =
will always be false!
COALESCE(list)
NULL element in list: mysql> select COALESCE(NULL,1);
-> 1
mysql> select COALESCE(NULL,NULL,NULL);
-> NULL
INTERVAL(N,N1,N2,N3,...)
0 if N < N1,
1 if N < N2 and so on. All arguments
are treated as integers. It is required that N1 <
N2 < N3 < ... <
Nn for this function to work correctly. This is because a binary
search is used (very fast): mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200);
-> 3
mysql> select INTERVAL(10, 1, 10, 100, 1000);
-> 2
mysql> select INTERVAL(22, 23, 30, 44, 200);
-> 0
If you are comparing case sensitive string with any of the standard operators
(=, <>..., but not LIKE) end space
will be ignored.
mysql> select "a" ="A ";
-> 1
All logical functions return 1 (TRUE), 0 (FALSE) or
NULL (unknown, which is in most cases the same as FALSE):
NOT
!
1 if the argument is 0,
otherwise returns 0. Exception: NOT NULL returns
NULL: mysql> select NOT 1;
-> 0
mysql> select NOT NULL;
-> NULL
mysql> select ! (1+1);
-> 0
mysql> select ! 1+1;
-> 1
The last example returns 1 because the expression evaluates
the same way as (!1)+1.
OR
||
1 if either argument is not
0 and not NULL: mysql> select 1 || 0;
-> 1
mysql> select 0 || 0;
-> 0
mysql> select 1 || NULL;
-> 1
AND
&&
0 if either argument is 0
or NULL, otherwise returns 1: mysql> select 1 && NULL;
-> 0
mysql> select 1 && 0;
-> 0
IFNULL(expr1,expr2)
expr1 is not
NULL, IFNULL() returns expr1, else it
returns expr2. IFNULL() returns a numeric or string
value, depending on the context in which it is used: mysql> select IFNULL(1,0);
-> 1
mysql> select IFNULL(NULL,10);
-> 10
mysql> select IFNULL(1/0,10);
-> 10
mysql> select IFNULL(1/0,'yes');
-> 'yes'
NULLIF(expr1,expr2)
expr1 = expr2 is true, return NULL else
return expr1. This is the same as CASE WHEN x = y THEN NULL
ELSE x END: mysql> select NULLIF(1,1);
-> NULL
mysql> select NULLIF(1,2);
-> 1
Note that expr1 is evaluated twice in MySQL if the
arguments are equal.
IF(expr1,expr2,expr3)
expr1 is TRUE (expr1 <> 0 and
expr1 <> NULL) then IF() returns
expr2, else it returns expr3. IF()
returns a numeric or string value, depending on the context in which it is
used: mysql> select IF(1>2,2,3);
-> 3
mysql> select IF(1<2,'yes','no');
-> 'yes'
mysql> select IF(strcmp('test','test1'),'no','yes');
-> 'no'
expr1 is evaluated as an integer value, which means that if
you are testing floating-point or string values, you should do so using a
comparison operation: mysql> select IF(0.1,1,0);
-> 0
mysql> select IF(0.1<>0,1,0);
-> 1
In the first case above, IF(0.1) returns 0
because 0.1 is converted to an integer value, resulting in a test
of IF(0). This may not be what you expect. In the second case,
the comparison tests the original floating-point value to see whether it is
non-zero. The result of the comparison is used as an integer. The default
return type of IF() (which may matter when it is stored into a
temporary table) is calculated in MySQL Version 3.23 as follows:
| Expression | Return value |
| expr2 or expr3 returns string | string |
| expr2 or expr3 returns a floating-point value | floating-point |
| expr2 or expr3 returns an integer | integer |
CASE value WHEN [compare-value] THEN result [WHEN [compare-value]
THEN result ...] [ELSE result] END
CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...]
[ELSE result] END
result where
value=compare-value. The second version returns the result for
the first condition, which is true. If there was no matching result value,
then the result after ELSE is returned. If there is no
ELSE part then NULL is returned: mysql> SELECT CASE 1 WHEN 1 THEN "one" WHEN 2 THEN "two" ELSE "more" END;
-> "one"
mysql> SELECT CASE WHEN 1>0 THEN "true" ELSE "false" END;
-> "true"
mysql> SELECT CASE BINARY "B" when "a" then 1 when "b" then 2 END;
-> NULL
The type of the return value (INTEGER, DOUBLE or
STRING) is the same as the type of the first returned value (the
expression after the first THEN).
String-valued functions return NULL if the length of the result
would be greater than the max_allowed_packet server parameter. See
section 5.5.2
Tuning Server Parameters.
For functions that operate on string positions, the first position is numbered 1.
ASCII(str)
str. Returns 0 if str is
the empty string. Returns NULL if str is
NULL: mysql> select ASCII('2');
-> 50
mysql> select ASCII(2);
-> 50
mysql> select ASCII('dx');
-> 100
See also the ORD() function.
ORD(str)
((first byte ASCII code)*256+(second
byte ASCII code))[*256+third byte ASCII code...]. If the leftmost
character is not a multi-byte character, returns the same value as the like
ASCII() function does: mysql> select ORD('2');
-> 50
CONV(N,from_base,to_base)
N, converted from base
from_base to base to_base. Returns NULL
if any argument is NULL. The argument N is
interpreted as an integer, but may be specified as an integer or a string. The
minimum base is 2 and the maximum base is 36. If
to_base is a negative number, N is regarded as a
signed number. Otherwise, N is treated as unsigned.
CONV works with 64-bit precision: mysql> select CONV("a",16,2);
-> '1010'
mysql> select CONV("6E",18,8);
-> '172'
mysql> select CONV(-17,10,-18);
-> '-H'
mysql> select CONV(10+"10"+'10'+0xa,10,10);
-> '40'
BIN(N)
N,
where N is a longlong (BIGINT) number. This is
equivalent to CONV(N,10,2). Returns NULL if
N is NULL: mysql> select BIN(12);
-> '1100'
OCT(N)
N,
where N is a longlong number. This is equivalent to
CONV(N,10,8). Returns NULL if N is
NULL: mysql> select OCT(12);
-> '14'
HEX(N_or_S)
N, where N is a longlong
(BIGINT) number. This is equivalent to
CONV(N,10,16). If N_OR_S is a string, returns a hexadecimal
string of N_OR_S where each character in N_OR_S is converted to 2 hexadecimal
digits. This is the invers of the 0xff strings. mysql> select HEX(255);
-> 'FF'
mysql> select HEX("abc");
-> 616263
mysql> select 0x616263;
-> "abc"
CHAR(N,...)
CHAR() interprets the arguments as integers and returns a
string consisting of the characters given by the ASCII code values of those
integers. NULL values are skipped: mysql> select CHAR(77,121,83,81,'76');
-> 'MySQL'
mysql> select CHAR(77,77.3,'77.3');
-> 'MMM'
CONCAT(str1,str2,...)
NULL if any argument is NULL. May have more than 2
arguments. A numeric argument is converted to the equivalent string form: mysql> select CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> select CONCAT('My', NULL, 'QL');
-> NULL
mysql> select CONCAT(14.3);
-> '14.3'
CONCAT_WS(separator, str1, str2,...)
CONCAT_WS() stands for CONCAT With Separator and is a special
form of CONCAT(). The first argument is the separator for the
rest of the arguments. The separator can be a string as well as the rest of
the arguments. If the separator is NULL, the result will be
NULL. The function will skip any NULLs and empty
strings, after the separator argument. The separator will be added between the
strings to be concatenated: mysql> select CONCAT_WS(",","First name","Second name","Last Name");
-> 'First name,Second name,Last Name'
mysql> select CONCAT_WS(",","First name",NULL,"Last Name");
-> 'First name,Last Name'
LENGTH(str)
OCTET_LENGTH(str)
CHAR_LENGTH(str)
CHARACTER_LENGTH(str)
str: mysql> select LENGTH('text');
-> 4
mysql> select OCTET_LENGTH('text');
-> 4
Note that for CHAR_LENGTH(), multi-byte characters are only
counted once.
LOCATE(substr,str)
POSITION(substr IN str)
substr in string str. Returns 0 if
substr is not in str: mysql> select LOCATE('bar', 'foobarbar');
-> 4
mysql> select LOCATE('xbar', 'foobar');
-> 0
This function is multi-byte safe. In MySQL 3.23 this function is case
insensitive, while in 4.0 it's only case insensitive if either argument is a
binary string.
LOCATE(substr,str,pos)
substr in string str, starting at position
pos. Returns 0 if substr is not in
str: mysql> select LOCATE('bar', 'foobarbar',5);
-> 7
This function is multi-byte safe. In MySQL 3.23 this function is case
insensitive, while in 4.0 it's only case insensitive if either argument is a
binary string.
INSTR(str,substr)
substr in string str. This is the same as the
two-argument form of LOCATE(), except that the arguments are
swapped: mysql> select INSTR('foobarbar', 'bar');
-> 4
mysql> select INSTR('xbar', 'foobar');
-> 0
This function is multi-byte safe. In MySQL 3.23 this function is case
insensitive, while in 4.0 it's only case insensitive if either argument is a
binary string.
LPAD(str,len,padstr)
str, left-padded with the string
padstr until str is len characters
long. If str is longer than len' then it will be
shortened to len characters. mysql> select LPAD('hi',4,'??');
-> '??hi'
RPAD(str,len,padstr)
str, right-padded with the string
padstr until str is len characters
long. If str is longer than len' then it will be
shortened to len characters. mysql> select RPAD('hi',5,'?');
-> 'hi???'
LEFT(str,len)
len characters from the string
str: mysql> select LEFT('foobarbar', 5);
-> 'fooba'
This function is multi-byte safe.
RIGHT(str,len)
len characters from the string
str: mysql> select RIGHT('foobarbar', 4);
-> 'rbar'
This function is multi-byte safe.
SUBSTRING(str,pos,len)
SUBSTRING(str FROM pos FOR len)
MID(str,pos,len)
len characters long from string
str, starting at position pos. The variant form that
uses FROM is ANSI SQL92 syntax: mysql> select SUBSTRING('Quadratically',5,6);
-> 'ratica'
This function is multi-byte safe.
SUBSTRING(str,pos)
SUBSTRING(str FROM pos)
str starting at position
pos: mysql> select SUBSTRING('Quadratically',5);
-> 'ratically'
mysql> select SUBSTRING('foobarbar' FROM 4);
-> 'barbar'
This function is multi-byte safe.
SUBSTRING_INDEX(str,delim,count)
str before
count occurrences of the delimiter delim. If
count is positive, everything to the left of the final delimiter
(counting from the left) is returned. If count is negative,
everything to the right of the final delimiter (counting from the right) is
returned: mysql> select SUBSTRING_INDEX('www.mysql.com', '.', 2);
-> 'www.mysql'
mysql> select SUBSTRING_INDEX('www.mysql.com', '.', -2);
-> 'mysql.com'
This function is multi-byte safe.
LTRIM(str)
str with leading space characters removed:
mysql> select LTRIM(' barbar');
-> 'barbar'
RTRIM(str)
str with trailing space characters
removed: mysql> select RTRIM('barbar ');
-> 'barbar'
This function is multi-byte safe.
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
str with all remstr prefixes
and/or suffixes removed. If none of the specifiers BOTH,
LEADING or TRAILING are given, BOTH is
assumed. If remstr is not specified, spaces are removed: mysql> select TRIM(' bar ');
-> 'bar'
mysql> select TRIM(LEADING 'x' FROM 'xxxbarxxx');
-> 'barxxx'
mysql> select TRIM(BOTH 'x' FROM 'xxxbarxxx');
-> 'bar'
mysql> select TRIM(TRAILING 'xyz' FROM 'barxxyz');
-> 'barx'
This function is multi-byte safe.
SOUNDEX(str)
str. Two strings that sound
almost the same should have identical soundex strings. A standard soundex
string is 4 characters long, but the SOUNDEX() function returns
an arbitrarily long string. You can use SUBSTRING() on the result
to get a standard soundex string. All non-alphanumeric characters are ignored
in the given string. All international alpha characters outside the A-Z range
are treated as vowels: mysql> select SOUNDEX('Hello');
-> 'H400'
mysql> select SOUNDEX('Quadratically');
-> 'Q36324'
SPACE(N)
N space characters: mysql> select SPACE(6);
-> ' '
REPLACE(str,from_str,to_str)
str with all all occurrences of the string
from_str replaced by the string to_str: mysql> select REPLACE('www.mysql.com', 'w', 'Ww');
-> 'WwWwWw.mysql.com'
This function is multi-byte safe.
REPEAT(str,count)
str repeated
count times. If count <= 0, returns an empty
string. Returns NULL if str or count
are NULL: mysql> select REPEAT('MySQL', 3);
-> 'MySQLMySQLMySQL'
REVERSE(str)
str with the order of the characters
reversed: mysql> select REVERSE('abc');
-> 'cba'
This function is multi-byte safe.
INSERT(str,pos,len,newstr)
str, with the substring beginning at
position pos and len characters long replaced by the
string newstr: mysql> select INSERT('Quadratic', 3, 4, 'What');
-> 'QuWhattic'
This function is multi-byte safe.
ELT(N,str1,str2,str3,...)
str1 if N = 1,
str2 if N = 2, and so on. Returns
NULL if N is less than 1 or greater
than the number of arguments. ELT() is the complement of
FIELD(): mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo');
-> 'ej'
mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo');
-> 'foo'
FIELD(str,str1,str2,str3,...)
str in the str1,
str2, str3, ... list. Returns
0 if str is not found. FIELD() is the
complement of ELT(): mysql> select FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 2
mysql> select FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 0
FIND_IN_SET(str,strlist)
1 to N if the string
str is in the list strlist consisting of
N substrings. A string list is a string composed of substrings
separated by `,' characters. If the first argument is a constant
string and the second is a column of type SET, the
FIND_IN_SET() function is optimised to use bit arithmetic!
Returns 0 if str is not in strlist or
if strlist is the empty string. Returns NULL if
either argument is NULL. This function will not work properly if
the first argument contains a `,': mysql> SELECT FIND_IN_SET('b','a,b,c,d');
-> 2
MAKE_SET(bits,str1,str2,...)
bits set. str1 corresponds to
bit 0, str2 to bit 1, etc. NULL strings in
str1, str2, ... are not appended to the
result: mysql> SELECT MAKE_SET(1,'a','b','c');
-> 'a'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
-> 'hello,world'
mysql> SELECT MAKE_SET(0,'a','b','c');
-> ''
EXPORT_SET(bits,on,off,[separator,[number_of_bits]])
mysql> select EXPORT_SET(5,'Y','N',',',4)
-> Y,N,Y,N
LCASE(str)
LOWER(str)
str with all characters changed to
lowercase according to the current character set mapping (the default is
ISO-8859-1 Latin1): mysql> select LCASE('QUADRATICALLY');
-> 'quadratically'
This function is multi-byte safe.
UCASE(str)
UPPER(str)
str with all characters changed to
uppercase according to the current character set mapping (the default is
ISO-8859-1 Latin1): mysql> select UCASE('Hej');
-> 'HEJ'
This function is multi-byte safe.
LOAD_FILE(file_name)
max_allowed_packet. If the file doesn't exist or
can't be read due to one of the above reasons, the function returns
NULL: mysql> UPDATE table_name
SET blob_column=LOAD_FILE("/tmp/picture")
WHERE id=1;
If you are not using MySQL Version 3.23, you have to do the reading of the
file inside your application and create an INSERT statement to
update the database with the file information. One way to do this, if you are
using the MySQL++ library, can be found at http://mysql.com/documentation/mysql++/mysql++-examples.html.
MySQL automatically converts numbers to strings as necessary, and vice-versa:
mysql> SELECT 1+"1";
-> 2
mysql> SELECT CONCAT(2,' test');
-> '2 test'
If you want to convert a number to a string explicitly, pass it as the
argument to CONCAT().
If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons.
Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.
expr LIKE pat [ESCAPE 'escape-char']
1 (TRUE) or 0 (FALSE). With
LIKE you can use the following two wild-card characters in the
pattern:
| Char | Description |
% |
Matches any number of characters, even zero characters |
_ |
Matches exactly one character |
mysql> select 'David!' LIKE 'David_';
-> 1
mysql> select 'David!' LIKE '%D%v%';
-> 1
To test for literal instances of a wild-card character, precede the
character with the escape character. If you don't specify the
ESCAPE character, `\' is assumed:
| String | Description |
\% |
Matches one % character |
\_ |
Matches one _ character |
mysql> select 'David!' LIKE 'David\_';
-> 0
mysql> select 'David_' LIKE 'David\_';
-> 1
To specify a different escape character, use the ESCAPE
clause: mysql> select 'David_' LIKE 'David|_' ESCAPE '|';
-> 1
The following two statements illustrate that string comparisons are case
insensitive unless one of the operands is a binary string: mysql> select 'abc' LIKE 'ABC';
-> 1
mysql> SELECT 'abc' LIKE BINARY 'ABC';
-> 0
LIKE is allowed on numeric expressions! (This is a MySQL
extension to the ANSI SQL LIKE.) mysql> select 10 LIKE '1%';
-> 1
Note: Because MySQL uses the C escape syntax in strings (for example,
`\n'), you must double any `\' that you use in your
LIKE strings. For example, to search for `\n',
specify it as `\\n'. To search for `\', specify it
as `\\\\' (the backslashes are stripped once by the parser and
another time when the pattern match is done, leaving a single backslash to be
matched).
expr NOT LIKE pat [ESCAPE 'escape-char']
NOT (expr LIKE pat [ESCAPE 'escape-char']).
expr REGEXP pat
expr RLIKE pat
expr against
a pattern pat. The pattern can be an extended regular expression.
See section G
Description of MySQL regular expression syntax. Returns 1 if
expr matches pat, otherwise returns 0.
RLIKE is a synonym for REGEXP, provided for
mSQL compatibility. Note: Because MySQL uses the C escape syntax
in strings (for example, `\n'), you must double any
`\' that you use in your REGEXP strings. As of MySQL
Version 3.23.4, REGEXP is case insensitive for normal (not
binary) strings: mysql> select 'Monty!' REGEXP 'm%y%%';
-> 0
mysql> select 'Monty!' REGEXP '.*';
-> 1
mysql> select 'new*\n*line' REGEXP 'new\\*.\\*line';
-> 1
mysql> select "a" REGEXP "A", "a" REGEXP BINARY "A";
-> 1 0
mysql> select "a" REGEXP "^[a-d]";
-> 1
REGEXP and RLIKE use the current character set
(ISO-8859-1 Latin1 by default) when deciding the type of a character.
expr NOT REGEXP pat
expr NOT RLIKE pat
NOT (expr REGEXP pat).
STRCMP(expr1,expr2)
STRCMP() returns 0 if the strings are the same,
-1 if the first argument is smaller than the second according to
the current sort order, and 1 otherwise: mysql> select STRCMP('text', 'text2');
-> -1
mysql> select STRCMP('text2', 'text');
-> 1
mysql> select STRCMP('text', 'text');
-> 0
MATCH (col1,col2,...) AGAINST (expr)
MATCH (col1,col2,...) AGAINST (expr IN BOOLEAN MODE)
MATCH ... AGAINST() is used for full-text search and returns
relevance - similarity measure between the text in columns
(col1,col2,...) and the query expr. Relevance is a
positive floating-point number. Zero relevance means no similarity.
MATCH ... AGAINST() is available in MySQL version 3.23.23 or
later. IN BOOLEAN MODE extension was added in version 4.0.1. For
details and usage examples see section 6.8
MySQL Full-text Search. BINARYBINARY operator casts the string
following it to a binary string. This is an easy way to force a column
comparison to be case sensitive even if the column isn't defined as
BINARY or BLOB: mysql> select "a" = "A";
-> 1
mysql> select BINARY "a" = "A";
-> 0
BINARY was introduced in MySQL Version 3.23.0. Note that in
some context MySQL will not be able to use the index efficiently when you cast
an indexed column to BINARY. If you want to compare a blob case-insensitively you can always convert the blob to upper case before doing the comparison:
SELECT 'A' LIKE UPPER(blob_col) FROM table_name;
We plan to soon introduce casting between different character sets to make string comparison even more flexible.
The usual arithmetic operators are available. Note that in the case of
`-', `+', and `*', the result is
calculated with BIGINT (64-bit) precision if both arguments are
integers!
+
mysql> select 3+5;
-> 8
-
mysql> select 3-5;
-> -2
*
mysql> select 3*5;
-> 15
mysql> select 18014398509481984*18014398509481984.0;
-> 324518553658426726783156020576256.0
mysql> select 18014398509481984*18014398509481984;
-> 0
The result of the last expression is incorrect because the result of the
integer multiplication exceeds the 64-bit range of BIGINT
calculations.
/
mysql> select 3/5;
-> 0.60
Division by zero produces a NULL result: mysql> select 102/(1-1);
-> NULL
A division will be calculated with BIGINT arithmetic only
if performed in a context where its result is converted to an integer!
All mathematical functions return NULL in case of an error.
-
mysql> select - 2;
-> -2
Note that if this operator is used with a BIGINT, the
return value is a BIGINT! This means that you should avoid using
- on integers that may have the value of -2^63!
ABS(X)
X: mysql> select ABS(2);
-> 2
mysql> select ABS(-32);
-> 32
This function is safe to use with BIGINT values.
SIGN(X)
-1, 0, or
1, depending on whether X is negative, zero, or
positive: mysql> select SIGN(-32);
-> -1
mysql> select SIGN(0);
-> 0
mysql> select SIGN(234);
-> 1
MOD(N,M)
%
% operator in C). Returns the remainder of
N divided by M: mysql> select MOD(234, 10);
-> 4
mysql> select 253 % 7;
-> 1
mysql> select MOD(29,9);
-> 2
This function is safe to use with BIGINT values.
FLOOR(X)
X: mysql> select FLOOR(1.23);
-> 1
mysql> select FLOOR(-1.23);
-> -2
Note that the return value is converted to a BIGINT!
CEILING(X)
X: mysql> select CEILING(1.23);
-> 2
mysql> select CEILING(-1.23);
-> -1
Note that the return value is converted to a BIGINT!
ROUND(X)
X, rounded to the nearest integer: mysql> select ROUND(-1.23);
-> -1
mysql> select ROUND(-1.58);
-> -2
mysql> select ROUND(1.58);
-> 2
Note that the behavior of ROUND() when the argument is half
way between two integers depends on the C library implementation. Some round
to the nearest even number, always up, always down, or always towards zero. If
you need one kind of rounding, you should use a well-defined function like
TRUNCATE() or FLOOR() instead.
ROUND(X,D)
X, rounded to a number with
D decimals. If D is 0, the result will
have no decimal point or fractional part: mysql> select ROUND(1.298, 1);
-> 1.3
mysql> select ROUND(1.298, 0);
-> 1
EXP(X)
e (the base of natural logarithms)
raised to the power of X: mysql> select EXP(2);
-> 7.389056
mysql> select EXP(-2);
-> 0.135335
LOG(X)
X: mysql> select LOG(2);
-> 0.693147
mysql> select LOG(-2);
-> NULL
If you want the log of a number X to some arbitary base
B, use the formula LOG(X)/LOG(B).
LOG10(X)
X: mysql> select LOG10(2);
-> 0.301030
mysql> select LOG10(100);
-> 2.000000
mysql> select LOG10(-100);
-> NULL
POW(X,Y)
POWER(X,Y)
X raised to the power of Y:
mysql> select POW(2,2);
-> 4.000000
mysql> select POW(2,-2);
-> 0.250000
SQRT(X)
X: mysql> select SQRT(4);
-> 2.000000
mysql> select SQRT(20);
-> 4.472136
PI()
mysql> select PI();
-> 3.141593
mysql> SELECT PI()+0.000000000000000000;
-> 3.141592653589793116
COS(X)
X, where X is given in
radians: mysql> select COS(PI());
-> -1.000000
SIN(X)
X, where X is given in
radians: mysql> select SIN(PI());
-> 0.000000
TAN(X)
X, where X is given in
radians: mysql> select TAN(PI()+1);
-> 1.557408
ACOS(X)
X, that is, the value whose cosine
is X. Returns NULL if X is not in the
range -1 to 1: mysql> select ACOS(1);
-> 0.000000
mysql> select ACOS(1.0001);
-> NULL
mysql> select ACOS(0);
-> 1.570796
ASIN(X)
X, that is, the value whose sine is
X. Returns NULL if X is not in the
range -1 to 1: mysql> select ASIN(0.2);
-> 0.201358
mysql> select ASIN('foo');
-> 0.000000
ATAN(X)
X, that is, the value whose
tangent is X: mysql> select ATAN(2);
-> 1.107149
mysql> select ATAN(-2);
-> -1.107149
ATAN(Y,X)
ATAN2(Y,X)
X and
Y. It is similar to calculating the arc tangent of Y /
X, except that the signs of both arguments are used to determine the
quadrant of the result: mysql> select ATAN(-2,2);
-> -0.785398
mysql> select ATAN2(PI(),0);
-> 1.570796
COT(X)
X: mysql> select COT(12);
-> -1.57267341
mysql> select COT(0);
-> NULL
RAND()
RAND(N)
0 to
1.0. If an integer argument N is specified, it is
used as the seed value: mysql> select RAND();
-> 0.9233482386203
mysql> select RAND(20);
-> 0.15888261251047
mysql> select RAND(20);
-> 0.15888261251047
mysql> select RAND();
-> 0.63553050033332
mysql> select RAND();
-> 0.70100469486881
You can't use a column with RAND() values in an ORDER
BY clause, because ORDER BY would evaluate the column
multiple times. In MySQL Version 3.23, you can, however, do: SELECT *
FROM table_name ORDER BY RAND() This is useful to get a random sample
of a set SELECT * FROM table1,table2 WHERE a=b AND c<d ORDER BY
RAND() LIMIT 1000. Note that a RAND() in a
WHERE clause will be re-evaluated every time the
WHERE is executed. RAND() is not meant to be a
perfect random generator, but instead a fast way to generate add-hook random
numbers that will be portable between platforms for the same MySQL version.
LEAST(X,Y,...)
INTEGER context, or all
arguments are integer-valued, they are compared as integers.
REAL context, or all
arguments are real-valued, they are compared as reals.
mysql> select LEAST(2,0);
-> 0
mysql> select LEAST(34.0,3.0,5.0,767.0);
-> 3.0
mysql> select LEAST("B","A","C");
-> "A"
In MySQL versions prior to Version 3.22.5, you can use
MIN() instead of LEAST.
GREATEST(X,Y,...)
LEAST: mysql> select GREATEST(2,0);
-> 2
mysql> select GREATEST(34.0,3.0,5.0,767.0);
-> 767.0
mysql> select GREATEST("B","A","C");
-> "C"
In MySQL versions prior to Version 3.22.5, you can use
MAX() instead of GREATEST.
DEGREES(X)
X, converted from radians to degrees: mysql> select DEGREES(PI());
-> 180.000000
RADIANS(X)
X, converted from degrees to radians: mysql> select RADIANS(90);
-> 1.570796
TRUNCATE(X,D)
X, truncated to D decimals.
If D is 0, the result will have no decimal point or
fractional part: mysql> select TRUNCATE(1.223,1);
-> 1.2
mysql> select TRUNCATE(1.999,1);
-> 1.9
mysql> select TRUNCATE(1.999,0);
-> 1
Note that as decimal numbers are normally not stored as exact numbers in
computers, but as double values, you may be fooled by the following result: mysql> select TRUNCATE(10.28*100,0);
-> 1027
The above happens because 10.28 is actually stored as something like
10.2799999999999999. See section 6.2.2 Date and Time Types for a description of the range of values each type has and the valid formats in which date and time values may be specified.
Here is an example that uses date functions. The query below selects all
records with a date_col value from within the last 30 days:
mysql> SELECT something FROM table
WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;
DAYOFWEEK(date)
date
(1 = Sunday, 2 = Monday, ... 7 =
Saturday). These index values correspond to the ODBC standard: mysql> select DAYOFWEEK('1998-02-03');
-> 3
WEEKDAY(date)
date (0 = Monday,
1 = Tuesday, ... 6 = Sunday): mysql> select WEEKDAY('1997-10-04 22:23:00');
-> 5
mysql> select WEEKDAY('1997-11-05');
-> 2
DAYOFMONTH(date)
date, in the range
1 to 31: mysql> select DAYOFMONTH('1998-02-03');
-> 3
DAYOFYEAR(date)
date, in the range
1 to 366: mysql> select DAYOFYEAR('1998-02-03');
-> 34
MONTH(date)
date, in the range 1 to
12: mysql> select MONTH('1998-02-03');
-> 2
DAYNAME(date)
date: mysql> select DAYNAME("1998-02-05");
-> 'Thursday'
MONTHNAME(date)
date: mysql> select MONTHNAME("1998-02-05");
-> 'February'
QUARTER(date)
date, in the range
1 to 4: mysql> select QUARTER('98-04-01');
-> 2
WEEK(date)
WEEK(date,first)
date, in the
range 0 to 53 (yes, there may be the beginnings of a
week 53), for locations where Sunday is the first day of the week. The
two-argument form of WEEK() allows you to specify whether the
week starts on Sunday or Monday. The week starts on Sunday if the second
argument is 0, on Monday if the second argument is
1: mysql> select WEEK('1998-02-20');
-> 7
mysql> select WEEK('1998-02-20',0);
-> 7
mysql> select WEEK('1998-02-20',1);
-> 8
mysql> select WEEK('1998-12-31',1);
-> 53
Note: in Version 4.0, WEEK(#,0) was changed to match the
calendar in the USA.
YEAR(date)
date, in the range 1000 to
9999: mysql> select YEAR('98-02-03');
-> 1998
YEARWEEK(date)
YEARWEEK(date,first)
WEEK(). Note that the year may be
different from the year in the date argument for the first and the last week
of the year: mysql> select YEARWEEK('1987-01-01');
-> 198653
HOUR(time)
time, in the range 0 to
23: mysql> select HOUR('10:05:03');
-> 10
MINUTE(time)
time, in the range 0 to
59: mysql> select MINUTE('98-02-03 10:05:03');
-> 5
SECOND(time)
time, in the range 0 to
59: mysql> select SECOND('10:05:03');
-> 3
PERIOD_ADD(P,N)
N months to period P (in the format
YYMM or YYYYMM). Returns a value in the format
YYYYMM. Note that the period argument P is
not a date value: mysql> select PERIOD_ADD(9801,2);
-> 199803
PERIOD_DIFF(P1,P2)
P1 and
P2. P1 and P2 should be in the format
YYMM or YYYYMM. Note that the period arguments
P1 and P2 are not date values: mysql> select PERIOD_DIFF(9802,199703);
-> 11
DATE_ADD(date,INTERVAL expr type)
DATE_SUB(date,INTERVAL expr type)
ADDDATE(date,INTERVAL expr type)
SUBDATE(date,INTERVAL expr type)
ADDDATE() and SUBDATE() are synonyms for
DATE_ADD() and DATE_SUB(). In MySQL Version 3.23,
you can use + and - instead of
DATE_ADD() and DATE_SUB() if the expression on the
right side is a date or datetime column. (See example) date is a
DATETIME or DATE value specifying the starting date.
expr is an expression specifying the interval value to be added
or subtracted from the starting date. expr is a string; it may
start with a `-' for negative intervals. type is a
keyword indicating how the expression should be interpreted. The related
function EXTRACT(type FROM date) returns the 'type' interval from
the date. The following table shows how the type and
expr arguments are related:
type value |
Expected expr format
|
SECOND |
SECONDS |
MINUTE |
MINUTES |
HOUR |
HOURS |
DAY |
DAYS |
MONTH |
MONTHS |
YEAR |
YEARS |
MINUTE_SECOND |
"MINUTES:SECONDS" |
HOUR_MINUTE |
"HOURS:MINUTES" |
DAY_HOUR |
"DAYS HOURS" |
YEAR_MONTH |
"YEARS-MONTHS" |
HOUR_SECOND |
"HOURS:MINUTES:SECONDS" |
DAY_MINUTE |
"DAYS HOURS:MINUTES" |
DAY_SECOND |
"DAYS HOURS:MINUTES:SECONDS" |
expr format. Those shown
in the table are the suggested delimiters. If the date argument
is a DATE value and your calculations involve only
YEAR, MONTH, and DAY parts (that is, no
time parts), the result is a DATE value. Otherwise the result is
a DATETIME value: mysql> SELECT "1997-12-31 23:59:59" + INTERVAL 1 SECOND;
-> 1998-01-01 00:00:00
mysql> SELECT INTERVAL 1 DAY + "1997-12-31";
-> 1998-01-01
mysql> SELECT "1998-01-01" - INTERVAL 1 SECOND;
-> 1997-12-31 23:59:59
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL 1 SECOND);
-> 1998-01-01 00:00:00
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL 1 DAY);
-> 1998-01-01 23:59:59
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL "1:1" MINUTE_SECOND);
-> 1998-01-01 00:01:00
mysql> SELECT DATE_SUB("1998-01-01 00:00:00",
INTERVAL "1 1:1:1" DAY_SECOND);
-> 1997-12-30 22:58:59
mysql> SELECT DATE_ADD("1998-01-01 00:00:00",
INTERVAL "-1 10" DAY_HOUR);
-> 1997-12-30 14:00:00
mysql> SELECT DATE_SUB("1998-01-02", INTERVAL 31 DAY);
-> 1997-12-02
If you specify an interval value that is too short (does not include all
the interval parts that would be expected from the type keyword),
MySQL assumes you have left out the leftmost parts of the interval value. For
example, if you specify a type of DAY_SECOND, the
value of expr is expected to have days, hours, minutes, and
seconds parts. If you specify a value like "1:10", MySQL assumes
that the days and hours parts are missing and the value represents minutes and
seconds. In other words, "1:10" DAY_SECOND is interpreted in such
a way that it is equivalent to "1:10" MINUTE_SECOND. This is
analogous to the way that MySQL interprets TIME values as
representing elapsed time rather than as time of day. Note that if you add or
subtract a date value against something that contains a time part, the date
value will be automatically converted to a datetime value: mysql> select date_add("1999-01-01", interval 1 day);
-> 1999-01-02
mysql> select date_add("1999-01-01", interval 1 hour);
-> 1999-01-01 01:00:00
If you use really incorrect dates, the result is NULL. If
you add MONTH, YEAR_MONTH, or YEAR and
the resulting date has a day that is larger than the maximum day for the new
month, the day is adjusted to the maximum days in the new month: mysql> select DATE_ADD('1998-01-30', Interval 1 month);
-> 1998-02-28
Note from the preceding example that the word INTERVAL and
the type keyword are not case sensitive.
EXTRACT(type FROM date)
EXTRACT() function uses the same kinds of interval type
specifiers as DATE_ADD() or DATE_SUB(), but extracts
parts from the date rather than performing date arithmetic. mysql> SELECT EXTRACT(YEAR FROM "1999-07-02");
-> 1999
mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03");
-> 199907
mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03");
-> 20102
TO_DAYS(date)
date, returns a daynumber (the number of days
since year 0): mysql> select TO_DAYS(950501);
-> 728779
mysql> select TO_DAYS('1997-10-07');
-> 729669
TO_DAYS() is not intended for use with values that precede
the advent of the Gregorian calendar (1582), because it doesn't take into
account the days that were lost when the calendar was changed.
FROM_DAYS(N)
N, returns a DATE value: mysql> select FROM_DAYS(729669);
-> '1997-10-07'
FROM_DAYS() is not intended for use with values that
precede the advent of the Gregorian calendar (1582), because it doesn't take
into account the days that were lost when the calendar was changed.
DATE_FORMAT(date,format)
date value according to the format
string. The following specifiers may be used in the format
string:
| Specifier | Description |
%M |
Month name (January..December) |
%W |
Weekday name (Sunday..Saturday) |
%D |
Day of the month with English suffix (1st,
2nd, 3rd, etc.) |
%Y |
Year, numeric, 4 digits |
%y |
Year, numeric, 2 digits |
%X |
Year for the week where Sunday is the first day of the week, numeric, 4 digits, used with '%V' |
%x |
Year for the week, where Monday is the first day of the week, numeric, 4 digits, used with '%v' |
%a |
Abbreviated weekday name (Sun..Sat) |
%d |
Day of the month, numeric (00..31) |
%e |
Day of the month, numeric (0..31) |
%m |
Month, numeric (01..12) |
%c |
Month, numeric (1..12) |
%b |
Abbreviated month name (Jan..Dec) |
%j |
Day of year (001..366) |
%H |
Hour (00..23) |
%k |
Hour (0..23) |
%h |
Hour (01..12) |
%I |
Hour (01..12) |
%l |
Hour (1..12) |
%i |
Minutes, numeric (00..59) |
%r |
Time, 12-hour (hh:mm:ss [AP]M) |
%T |
Time, 24-hour (hh:mm:ss) |
%S |
Seconds (00..59) |
%s |
Seconds (00..59) |
%p |
AM or PM |
%w |
Day of the week (0=Sunday..6=Saturday)
|
%U |
Week (0..53), where Sunday is the first
day of the week |
%u |
Week (0..53), where Monday is the first
day of the week |
%V |
Week (1..53), where Sunday is the first
day of the week. Used with '%X' |
%v |
Week (1..53), where Monday is the first
day of the week. Used with '%x' |
%% |
A literal `%'. |
mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y');
-> 'Saturday October 1997'
mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s');
-> '22:23:00'
mysql> select DATE_FORMAT('1997-10-04 22:23:00',
'%D %y %a %d %m %b %j');
-> '4th 97 Sat 04 10 Oct 277'
mysql> select DATE_FORMAT('1997-10-04 22:23:00',
'%H %k %I %r %T %S %w');
-> '22 22 10 10:23:00 PM 22:23:00 00 6'
mysql> select DATE_FORMAT('1999-01-01', '%X %V');
-> '1998 52'
As of MySQL Version 3.23, the `%' character is required
before format specifier characters. In earlier versions of MySQL,
`%' was optional.
TIME_FORMAT(time,format)
DATE_FORMAT() function above, but the
format string may contain only those format specifiers that
handle hours, minutes, and seconds. Other specifiers produce a
NULL value or 0.
CURDATE()
CURRENT_DATE
'YYYY-MM-DD' or
YYYYMMDD format, depending on whether the function is used in a
string or numeric context: mysql> select CURDATE();
-> '1997-12-15'
mysql> select CURDATE() + 0;
-> 19971215
CURTIME()
CURRENT_TIME
'HH:MM:SS' or
HHMMSS format, depending on whether the function is used in a
string or numeric context: mysql> select CURTIME();
-> '23:50:26'
mysql> select CURTIME() + 0;
-> 235026
NOW()
SYSDATE()
CURRENT_TIMESTAMP
'YYYY-MM-DD
HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether
the function is used in a string or numeric context: mysql> select NOW();
-> '1997-12-15 23:50:26'
mysql> select NOW() + 0;
-> 19971215235026
UNIX_TIMESTAMP()
UNIX_TIMESTAMP(date)
'1970-01-01 00:00:00' GMT). If UNIX_TIMESTAMP() is
called with a date argument, it returns the value of the argument
as seconds since '1970-01-01 00:00:00' GMT. date may
be a DATE string, a DATETIME string, a
TIMESTAMP, or a number in the format YYMMDD or
YYYYMMDD in local time: mysql> select UNIX_TIMESTAMP();
-> 882226357
mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00');
-> 875996580
When UNIX_TIMESTAMP is used on a TIMESTAMP
column, the function will receive the value directly, with no implicit
``string-to-unix-timestamp'' conversion. If you give
UNIX_TIMESTAMP() a wrong or out-of-range date, it will return 0.
FROM_UNIXTIME(unix_timestamp)
unix_timestamp argument as a
value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS
format, depending on whether the function is used in a string or numeric
context: mysql> select FROM_UNIXTIME(875996580);
-> '1997-10-04 22:23:00'
mysql> select FROM_UNIXTIME(875996580) + 0;
-> 19971004222300
FROM_UNIXTIME(unix_timestamp,format)
format string. format may contain the same
specifiers as those listed in the entry for the DATE_FORMAT()
function: mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(),
'%Y %D %M %h:%i:%s %x');
-> '1997 23rd December 03:43:30 x'
SEC_TO_TIME(seconds)
seconds argument, converted to hours, minutes,
and seconds, as a value in 'HH:MM:SS' or HHMMSS
format, depending on whether the function is used in a string or numeric
context: mysql> select SEC_TO_TIME(2378);
-> '00:39:38'
mysql> select SEC_TO_TIME(2378) + 0;
-> 3938
TIME_TO_SEC(time)
time argument, converted to seconds: mysql> select TIME_TO_SEC('22:23:00');
-> 80580
mysql> select TIME_TO_SEC('00:39:38');
-> 2378
MySQL uses BIGINT (64-bit) arithmetic for bit operations, so
these operators have a maximum range of 64 bits.
|
mysql> select 29 | 15;
-> 31
&
mysql> select 29 & 15;
-> 13
<<
BIGINT) number to the left: mysql> select 1 << 2;
-> 4
>>
BIGINT) number to the right: mysql> select 4 >> 2;
-> 1
~
mysql> select 5 & ~1;
-> 4
BIT_COUNT(N)
N: mysql> select BIT_COUNT(29);
-> 4
DATABASE()
mysql> select DATABASE();
-> 'test'
If there is no current database, DATABASE() returns the
empty string.
USER()
SYSTEM_USER()
SESSION_USER()
mysql> select USER();
-> 'davida@localhost'
In MySQL Version 3.22.11 or later, this includes the client hostname as
well as the user name. You can extract just the user name part like this
(which works whether or not the value includes a hostname part): mysql> select substring_index(USER(),"@",1);
-> 'davida'
PASSWORD(str)
str.
This is the function that is used for encrypting MySQL passwords for storage
in the Password column of the user grant table: mysql> select PASSWORD('badpwd');
-> '7f84554057dd964b'
PASSWORD() encryption is
non-reversible. PASSWORD() does not perform password encryption
in the same way that Unix passwords are encrypted. You should not assume that
if your Unix password and your MySQL password are the same,
PASSWORD() will result in the same encrypted value as is stored
in the Unix password file. See ENCRYPT().
ENCRYPT(str[,salt])
str using the Unix crypt() system call.
The salt argument should be a string with two characters. (As of
MySQL Version 3.22.16, salt may be longer than two characters.): mysql> select ENCRYPT("hello");
-> 'VxuFAJXVARROc'
If crypt() is not available on your system,
ENCRYPT() always returns NULL.
ENCRYPT() ignores all but the first 8 characters of
str, at least on some systems. This will be determined by the
behavior of the underlying crypt() system call.
ENCODE(str,pass_str)
str using pass_str as the password. To
decrypt the result, use DECODE(). The results is a binary string
of the same length as string. If you want to save it in a column,
use a BLOB column type.
DECODE(crypt_str,pass_str)
crypt_str using
pass_str as the password. crypt_str should be a
string returned from ENCODE().
MD5(string)
mysql> select MD5("testing");
-> 'ae2b1fca515949e5d54fb22b8ed95575'
This is an "RSA Data Security, Inc. MD5 Message-Digest Algorithm".
des_encrypt(string_to_encrypt, flag, [, (key_number | key_string) ]
)
| Argument | Description |
| Only one argument | The first key from des-key-file is used. |
| key number | The given key (0-9) from the des-key-file is used.
|
| string | The given key_string will be used to crypt
string_to_encrypt. |
CHAR(128 |
key-number). The 128 is added to make it easier to recognize a crypted
key. If one uses a string key, key-number will be 127. On error,
this function returns NULL. The string length for the result will be
new_length= org_length + (8-(org_length % 8))+1. The
des-key-file has the following format: key-number key-string key-number key-stringThe
key-number must be a number between 0-9. The numbers
may be in any order. des-key-string is string that will be used
to crypt the message. Between the number and the key there should be at least
one space. The first key is the default key that will be used if one doesn't
specify a key to des_encrypt() You can tell MySQL to read new key
values from the key file with the FLUSH DES_KEY_FILE command. One
benefit with having a set of default keys on can use is that it gives
applications a way to check for existence of crypted column, without giving
the end user the right to uncrypt the data. SELECT customer_address FROM customer_table WHERE
crypted_credit_card = DES_ENCRYPT("credit_card_number");
des_decrypt(string_to_decrypt [, key_string])
des_encrypt(). Note that this
function only works if you have configured MySQL with SLL support. See section
4.3.8
Using Secure Connections. If one only gives this a string argument, then
it will use the right key from the des-key-file to decrypt the
message. For this to work the user must have the PROCESS_PRIV
privilege. If one calls this function with 2 arguments, the second argument is
used to decrypt the message. If the string_to_decrypt doesn't
look like a crypted string MySQL will return the given
string_to_decrypt. On error, this function returns NULL.
LAST_INSERT_ID([expr])
AUTO_INCREMENT column. See section 8.4.3.126
mysql_insert_id(). mysql> select LAST_INSERT_ID();
-> 195
The last ID that was generated is maintained in the server on a
per-connection basis. It will not be changed by another client. It will not
even be changed if you update another AUTO_INCREMENT column with
a non-magic value (that is, a value that is not NULL and not
0). If you insert many rows at the same time with an insert
statement, LAST_INSERT_ID() returns the value for the first
inserted row. The reason for this is so that you it makes it possible to
easily reproduce the same INSERT statement against some other
server. If expr is given as an argument to
LAST_INSERT_ID(), then the value of the argument is returned by
the function, is set as the next value to be returned by
LAST_INSERT_ID() and used as the next auto_increment value. This
can be used to simulate sequences: First create the table: mysql> create table sequence (id int not null); mysql> insert into sequence values (0);Then the table can be used to generate sequence numbers like this:
mysql> update sequence set id=LAST_INSERT_ID(id+1);You can generate sequences without calling
LAST_INSERT_ID(), but the utility of using the function this way
is that the ID value is maintained in the server as the last automatically
generated value. You can retrieve the new ID as you would read any normal
AUTO_INCREMENT value in MySQL. For example,
LAST_INSERT_ID() (without an argument) will return the new ID.
The C API function mysql_insert_id() can also be used to get the
value. Note that as mysql_insert_id() is only updated after
INSERT and UPDATE statements, you can't use this
function to retrieve the value for LAST_INSERT_ID(expr) after
executing other SQL statements like SELECT or SET.
FORMAT(X,D)
X to a format like
'#,###,###.##', rounded to D decimals. If
D is 0, the result will have no decimal point or
fractional part: mysql> select FORMAT(12332.123456, 4);
-> '12,332.1235'
mysql> select FORMAT(12332.1,4);
-> '12,332.1000'
mysql> select FORMAT(12332.2,0);
-> '12,332'
VERSION()
mysql> select VERSION();
-> '3.23.13-log'
Note that if your version ends with -log this means that
logging is enabled.
CONNECTION_ID()
thread_id) for the connection.
Every connection has its own unique id: mysql> select CONNECTION_ID();
-> 1
GET_LOCK(str,timeout)
str,
with a timeout of timeout seconds. Returns 1 if the
lock was obtained successfully, 0 if the attempt timed out, or
NULL if an error occurred (such as running out of memory or the
thread was killed with mysqladmin kill). A lock is released when
you execute RELEASE_LOCK(), execute a new
GET_LOCK(), or the thread terminates. This function can be used
to implement application locks or to simulate record locks. It blocks requests
by other clients for locks with the same name; clients that agree on a given
lock string name can use the string to perform cooperative advisory locking: mysql> select GET_LOCK("lock1",10);
-> 1
mysql> select GET_LOCK("lock2",10);
-> 1
mysql> select RELEASE_LOCK("lock2");
-> 1
mysql> select RELEASE_LOCK("lock1");
-> NULL
Note that the second RELEASE_LOCK() call returns
NULL because the lock "lock1" was automatically
released by the second GET_LOCK() call.
RELEASE_LOCK(str)
str that was obtained
with GET_LOCK(). Returns 1 if the lock was released,
0 if the lock wasn't locked by this thread (in which case the
lock is not released), and NULL if the named lock didn't exist.
The lock will not exist if it was never obtained by a call to
GET_LOCK() or if it already has been released. The
DO statement is convinient to use with
RELEASE_LOCK(). See section 6.4.10
DO Syntax.
BENCHMARK(count,expr)
BENCHMARK() function executes the expression
expr repeatedly count times. It may be used to time
how fast MySQL processes the expression. The result value is always
0. The intended use is in the mysql client, which
reports query execution times: mysql> select BENCHMARK(1000000,encode("hello","goodbye"));
+----------------------------------------------+
| BENCHMARK(1000000,encode("hello","goodbye")) |
+----------------------------------------------+
| 0 |
+----------------------------------------------+
1 row in set (4.74 sec)
The time reported is elapsed time on the client end, not CPU time on the
server end. It may be advisable to execute BENCHMARK() several
times, and interpret the result with regard to how heavily loaded the server
machine is.
INET_NTOA(expr)
mysql> select INET_NTOA(3520061480);
-> "209.207.224.40"
INET_ATON(expr)
mysql> select INET_ATON("209.207.224.40");
-> 3520061480
The generated number is always in network byte order; For example the
above number is calculated as 209*255^3 + 207*255^2 + 224*255
+40.
MASTER_POS_WAIT(log_name, log_pos)
GROUP BY
ClausesIf you use a group function in a statement containing no GROUP
BY clause, it is equivalent to grouping on all rows.
COUNT(expr)
NULL
values in the rows retrieved by a SELECT statement: mysql> select student.student_name,COUNT(*)
from student,course
where student.student_id=course.student_id
GROUP BY student_name;
COUNT(*) is somewhat different in that it returns a count
of the number of rows retrieved, whether or not they contain NULL
values. COUNT(*) is optimised to return very quickly if the
SELECT retrieves from one table, no other columns are retrieved,
and there is no WHERE clause. For example: mysql> select COUNT(*) from student;
COUNT(DISTINCT expr,[expr...])
NULL values: mysql> select COUNT(DISTINCT results) from student;In MySQL you can get the number of distinct expression combinations that don't contain NULL by giving a list of expressions. In ANSI SQL you would have to do a concatenation of all expressions inside
CODE(DISTINCT
..).
AVG(expr)
expr: mysql> select student_name, AVG(test_score)
from student
GROUP BY student_name;
MIN(expr)
MAX(expr)
expr.
MIN() and MAX() may take a string argument; in such
cases they return the minimum or maximum string value. See section 5.4.3
How MySQL Uses Indexes. mysql> select student_name, MIN(test_score), MAX(test_score)
from student
GROUP BY student_name;
SUM(expr)
expr. Note that if the return set has no
rows, it returns NULL!
STD(expr)
STDDEV(expr)
expr. This is an extension
to ANSI SQL. The STDDEV() form of this function is provided for
Oracle compatibility.
BIT_OR(expr)
OR of all bits in expr. The
calculation is performed with 64-bit (BIGINT) precision.
BIT_AND(expr)
AND of all bits in expr. The
calculation is performed with 64-bit (BIGINT) precision. MySQL has extended the use of GROUP BY. You
can use columns or calculations in the SELECT expressions that
don't appear in the GROUP BY part. This stands for any possible
value for this group. You can use this to get better performance by
avoiding sorting and grouping on unnecessary items. For example, you don't need
to group on customer.name in the following query:
mysql> select order.custid,customer.name,max(payments)
from order,customer
where order.custid = customer.custid
GROUP BY order.custid;
In ANSI SQL, you would have to add customer.name to the
GROUP BY clause. In MySQL, the name is redundant if you don't run
in ANSI mode.
Don't use this feature if the columns you omit from the
GROUP BY part aren't unique in the group! You will get
unpredictable results.
In some cases, you can use MIN() and MAX() to
obtain a specific column value even if it isn't unique. The following gives the
value of column from the row containing the smallest value in the
sort column:
substr(MIN(concat(rpad(sort,6,' '),column)),7)
See section 3.5.4 The Rows Holding the Group-wise Maximum of a Certain Field.
Note that if you are
using MySQL Version 3.22 (or earlier) or if you are trying to follow ANSI SQL,
you can't use expressions in GROUP BY or ORDER BY
clauses. You can work around this limitation by using an alias for the
expression:
mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name
GROUP BY id,val ORDER BY val;
In MySQL Version 3.23 you can do:
mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND();
SELECT,
INSERT, UPDATE, DELETESELECT SyntaxSELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[SQL_CACHE | SQL_NO_CACHE] [HIGH_PRIORITY]
[DISTINCT | DISTINCTROW | ALL]
select_expression,...
[INTO {OUTFILE | DUMPFILE} 'file_name' export_options]
[FROM table_references
[WHERE where_definition]
[GROUP BY {unsigned_integer | col_name | formula} [ASC | DESC], ...]
[HAVING where_definition]
[ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...]
[LIMIT [offset,] rows]
[PROCEDURE procedure_name]
[FOR UPDATE | LOCK IN SHARE MODE]]
SELECT is used to retrieve rows selected from one or more
tables. select_expression indicates the columns you want to
retrieve. SELECT may also be used to retrieve rows computed without
reference to any table. For example:
mysql> SELECT 1 + 1;
-> 2
All keywords used must be given in exactly the order shown above. For
example, a HAVING clause must come after any GROUP BY
clause and before any ORDER BY clause.
SELECT expression
may be given an alias using AS. The alias is used as the
expression's column name and can be used with ORDER BY or
HAVING clauses. For example: mysql> select concat(last_name,', ',first_name) AS full_name
from mytable ORDER BY full_name;
WHERE clause,
because the column value may not yet be determined when the WHERE
clause is executed. See section A.5.4
Problems with alias.
FROM table_references clause indicates the tables from
which to retrieve rows. If you name more than one table, you are performing a
join. For information on join syntax, see section 6.4.1.1
JOIN Syntax.
col_name,
tbl_name.col_name, or db_name.tbl_name.col_name. You
need not specify a tbl_name or db_name.tbl_name
prefix for a column reference in a SELECT statement unless the
reference would be ambiguous. See section 6.1.2
Database, Table, Index, Column, and Alias Names, for examples of ambiguity
that require the more explicit column reference forms.
tbl_name [AS] alias_name: mysql> select t1.name, t2.salary from employee AS t1, info AS t2
where t1.name = t2.name;
mysql> select t1.name, t2.salary from employee t1, info t2
where t1.name = t2.name;
ORDER BY
and GROUP BY clauses using column names, column aliases, or
column positions. Column positions begin with 1: mysql> select college, region, seed from tournament
ORDER BY region, seed;
mysql> select college, region AS r, seed AS s from tournament
ORDER BY r, s;
mysql> select college, region, seed from tournament
ORDER BY 2, 3;
To sort in reverse order, add the DESC (descending) keyword
to the name of the column in the ORDER BY clause that you are
sorting by. The default is ascending order; this may be specified explicitly
using the ASC keyword.
WHERE clause use any of the functions that
MySQL support. See section 6.3
Functions for Use in SELECT and WHERE Clauses.
HAVING clause can refer to any column or alias named in
the select_expression. It is applied last, just before items are
sent to the client, with no optimisation. Don't use HAVING for
items that should be in the WHERE clause. For example, do not
write this: mysql> select col_name from tbl_name HAVING col_name > 0;Write this instead:
mysql> select col_name from tbl_name WHERE col_name > 0;In MySQL Version 3.22.5 or later, you can also write queries like this:
mysql> select user,max(salary) from users
group by user HAVING max(salary)>10;
In older MySQL versions, you can write this instead: mysql> select user,max(salary) AS sum from users
group by user HAVING sum>10;
SQL_, STRAIGHT_JOIN,
and HIGH_PRIORITY are MySQL extensions to ANSI SQL.
HIGH_PRIORITY will give the SELECT higher
priority than a statement that updates a table. You should only use this for
queries that are very fast and must be done at once. A SELECT
HIGH_PRIORITY query will run if the table is locked for read even if
there is an update statement that is waiting for the table to be free.
SQL_BIG_RESULT can be used with GROUP BY or
DISTINCT to tell the optimiser that the result set will have many
rows. In this case, MySQL will directly use disk-based temporary tables if
needed. MySQL will also, in this case, prefer sorting to doing a temporary
table with a key on the GROUP BY elements.
SQL_BUFFER_RESULT will force the result to be put into a
temporary table. This will help MySQL free the table locks early and will help
in cases where it takes a long time to send the result set to the client.
SQL_SMALL_RESULT, a MySQL-specific option, can be used with
GROUP BY or DISTINCT to tell the optimiser that the
result set will be small. In this case, MySQL will use fast temporary tables
to store the resulting table instead of using sorting. In MySQL Version 3.23
this shouldn't normally be needed.
SQL_CACHE tells MySQL to store the query result in the query
cache if you are using SQL_QUERY_CACHE_TYPE=2
(DEMAND). See section 6.9
MySQL Query Cache.
SQL_NO_CACHE tells MySQL to not allow the query result to be
stored in the query cache. See section 6.9
MySQL Query Cache.
GROUP BY, the output rows will
be sorted according to the GROUP BY as if you would have had an
ORDER BY over all the fields in the GROUP BY. MySQL
has extended the GROUP BY so that you can also specify
ASC and DESC to GROUP BY: SELECT a,COUNT(b) FROM test_table GROUP BY a DESC
GROUP BY to allow you to select
fields which are not mentioned in the GROUP BY clause. If you are
not getting the results you expect from your query, please read the
GROUP BY description. See section 6.3.6
Functions for Use with GROUP BY Clauses.
SQL_BUFFER_RESULT will force the result
to be put into a temporary table. This will help MySQL free the table locks
early and will help in cases where it takes a long time to send the result set
to the client.
SQL_SMALL_RESULT, a MySQL-specific
option, can be used with GROUP BY or DISTINCT to
tell the optimiser that the result set will be small. In this case, MySQL will
use fast temporary tables to store the resulting table instead of using
sorting. In MySQL Version 3.23 this shouldn't normally be needed.
STRAIGHT_JOIN forces the optimiser to
join the tables in the order in which they are listed in the FROM
clause. You can use this to speed up a query if the optimiser joins the tables
in non-optimal order. See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
LIMIT clause can be used to constrain the number of rows
returned by the SELECT statement. LIMIT takes one or
two numeric arguments. If two arguments are given, the first specifies the
offset of the first row to return, the second specifies the maximum number of
rows to return. The offset of the initial row is 0 (not 1): mysql> select * from table LIMIT 5,10; # Retrieve rows 6-15If one argument is given, it indicates the maximum number of rows to return:
mysql> select * from table LIMIT 5; # Retrieve first 5 rowsIn other words,
LIMIT n is equivalent to LIMIT
0,n.
SELECT ... INTO OUTFILE 'file_name'
form of SELECT writes the selected rows to a file. The file is
created on the server host and cannot already exist (among other things, this
prevents database tables and files such as `/etc/passwd' from being
destroyed). You must have the file privilege on the server
host to use this form of SELECT. SELECT ... INTO
OUTFILE is mainly intended to let you very quickly dump a table on the
server machine. If you want to create the resulting file on some other host
than the server host you can't use SELECT ... INTO OUTFILE. In
this case you should instead use some client program like mysqldump
--tab or mysql -e "SELECT ..." > outfile to generate
the file. SELECT ... INTO OUTFILE is the complement of LOAD
DATA INFILE; the syntax for the export_options part of the
statement consists of the same FIELDS and LINES
clauses that are used with the LOAD DATA INFILE statement. See
section 6.4.9
LOAD DATA INFILE Syntax. In the resulting text file, only the
following characters are escaped by the ESCAPED BY character:
ESCAPED BY character
FIELDS TERMINATED BY
LINES TERMINATED BY
ASCII 0 is converted to ESCAPED
BY followed by 0 (ASCII 48). The reason for the above is
that you must escape any FIELDS TERMINATED BY,
ESCAPED BY, or LINES TERMINATED BY characters to
reliably be able to read the file back. ASCII 0 is escaped to
make it easier to view with some pagers. As the resulting file doesn't have to
conform to the SQL syntax, nothing else need be escaped. Here follows an
example of getting a file in the format used by many old programs. SELECT a,b,a+b INTO OUTFILE "/tmp/result.text" FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY "\n" FROM test_table;
INTO DUMPFILE instead of
INTO OUTFILE, MySQL will only write one row into the file,
without any column or line terminations and without any escaping. This is
useful if you want to store a blob in a file.
INTO OUTFILE and INTO
DUMPFILE is going to be readable for all users! The reason is that the
MySQL server can't create a file that is owned by anyone else than the user
it's running as (you should never run mysqld as root), the file
has to be word readable so that you can retrieve the rows.
FOR UPDATE on a table handler with page/row
locks, the examined rows will be write locked. JOIN SyntaxMySQL supports the following JOIN syntaxes for use in
SELECT statements:
table_reference, table_reference
table_reference [CROSS] JOIN table_reference
table_reference INNER JOIN table_reference join_condition
table_reference STRAIGHT_JOIN table_reference
table_reference LEFT [OUTER] JOIN table_reference join_condition
table_reference LEFT [OUTER] JOIN table_reference
table_reference NATURAL [LEFT [OUTER]] JOIN table_reference
{ oj table_reference LEFT OUTER JOIN table_reference ON conditional_expr }
table_reference RIGHT [OUTER] JOIN table_reference join_condition
table_reference RIGHT [OUTER] JOIN table_reference
table_reference NATURAL [RIGHT [OUTER]] JOIN table_reference
Where table_reference is defined as:
table_name [[AS] alias] [USE INDEX (key_list)] [IGNORE INDEX (key_list)]
and join_condition is defined as:
ON conditional_expr | USING (column_list)
You should never have any conditions in the ON part that are
used to restrict which rows you have in the result set. If you want to restrict
which rows should be in the result, you have to do this in the
WHERE clause.
Note that in versions before Version 3.23.17, the INNER JOIN
didn't take a join_condition!
The last LEFT OUTER JOIN
syntax shown above exists only for compatibility with ODBC:
tbl_name AS alias_name
or tbl_name alias_name: mysql> select t1.name, t2.salary from employee AS t1, info AS t2
where t1.name = t2.name;
ON conditional is any conditional of the form that may be
used in a WHERE clause.
ON
or USING part in a LEFT JOIN, a row with all columns
set to NULL is used for the right table. You can use this fact to
find records in a table that have no counterpart in another table: mysql> select table1.* from table1
LEFT JOIN table2 ON table1.id=table2.id
where table2.id is NULL;
This example finds all rows in table1 with an
id value that is not present in table2 (that is, all
rows in table1 with no corresponding row in table2).
This assumes that table2.id is declared NOT NULL, of
course. See section 5.2.6
How MySQL Optimises LEFT JOIN and RIGHT JOIN.
USING (column_list) clause names a list of
columns that must exist in both tables. A USING clause such as: A LEFT JOIN B USING (C1,C2,C3,...)is defined to be semantically identical to an
ON expression
like this: A.C1=B.C1 AND A.C2=B.C2 AND A.C3=B.C3,...
NATURAL [LEFT] JOIN of two tables is defined to be
semantically equivalent to an INNER JOIN or a LEFT
JOIN with a USING clause that names all columns that exist
in both tables.
INNER JOIN and , (comma) are
semantically equivalent. Both do a full join between the tables used.
Normally, you specify how the tables should be linked in the WHERE condition.
RIGHT JOIN works analogously as LEFT JOIN. To
keep code portable across databases, it's recommended to use LEFT
JOIN instead of RIGHT JOIN.
STRAIGHT_JOIN is identical to
JOIN, except that the left table is always read before the right
table. This can be used for those (few) cases where the join optimiser puts
the tables in the wrong order.
EXPLAIN shows that MySQL is using the wrong index. By
specifying USE INDEX (key_list), you can tell MySQL to use only
one of the specified indexes to find rows in the table. The alternative syntax
IGNORE INDEX (key_list) can be used to tell MySQL to not use some
particular index. Some examples:
mysql> select * from table1,table2 where table1.id=table2.id;
mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id;
mysql> select * from table1 LEFT JOIN table2 USING (id);
mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id
LEFT JOIN table3 ON table2.id=table3.id;
mysql> select * from table1 USE INDEX (key1,key2) WHERE key1=1 and key2=2 AND
key3=3;
mysql> select * from table1 IGNORE INDEX (key3) WHERE key1=1 and key2=2 AND
key3=3;
See section 5.2.6
How MySQL Optimises LEFT JOIN and RIGHT JOIN.
UNION SyntaxSELECT .... UNION [ALL] SELECT .... [UNION SELECT ...]
UNION is implemented in MySQL 4.0.0.
UNION is used to combine the result from many
SELECT statements into one result set.
The SELECT commands are normal select commands, but with the
following restrictions:
SELECT command can have INTO
OUTFILE.
SELECT command can have ORDER BY.
If you don't use the keyword ALL for the UNION, all
returned rows will be unique, like if you had done a DISTINCT for
the total result set. If you specify ALL, then you will get all
matching rows from all the used SELECT statements.
HANDLER SyntaxHANDLER table OPEN [ AS alias ]
HANDLER table READ index { = | >= | <= | < } (value1, value2, ... ) [ WHERE ... ] [LIMIT ... ]
HANDLER table READ index { FIRST | NEXT | PREV | LAST } [ WHERE ... ] [LIMIT ... ]
HANDLER table READ { FIRST | NEXT } [ WHERE ... ] [LIMIT ... ]
HANDLER table CLOSE
The HANDLER statement provides direct access to MySQL table
interface, bypassing SQL optimiser. Thus, it is faster then SELECT.
The first form of HANDLER statement opens a table, making in
accessible via the following HANDLER ... READ routines. This table
object is not shared by other threads an will not be closed until the thread
calls HANDLER table_name CLOSE or the thread dies.
The second form fetches one (or, specified by LIMIT clause) row
where the index specified complies to the condition and WHERE
condition is met. If the index consists of several parts (spans over several
columns) the values are specified in comma-separated list, providing values only
for few first columns is possible.
The third form fetches one (or, specified by LIMIT clause) row
from the table in index order, matching WHERE condition.
The fourth form (without index specification) fetches one (or, specified by
LIMIT clause) row from the table in natural row order (as stored in
data file) matching WHERE condition. It is faster than
HANDLER table READ index when full table scan is desired.
The last form closes the table, opened with HANDLER ... OPEN.
HANDLER is somewhat low-level statement, for example it does not
provide consistency. That is HANDLER ... OPEN does
NOT takes a snapshot of the table, and does
NOT locks the table. The above means, that after HANDLER
... OPEN table data can be modified (by this or other thread) and these
modifications may appear only partially in HANDLER ... NEXT or
HANDLER ... PREV scans.
INSERT Syntax INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name [(col_name,...)]
VALUES (expression,...),(...),...
or INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name [(col_name,...)]
SELECT ...
or INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name
SET col_name=expression, col_name=expression, ...
INSERT inserts new rows into an existing table. The INSERT
... VALUES form of the statement inserts rows based on explicitly
specified values. The INSERT ... SELECT form inserts rows selected
from another table or tables. The INSERT ... VALUES form with
multiple value lists is supported in MySQL Version 3.22.5 or later. The
col_name=expression syntax is supported in MySQL Version 3.22.10 or
later.
tbl_name is the table into which rows should be inserted. The
column name list or the SET clause indicates which columns the
statement specifies values for:
INSERT ... VALUES or
INSERT ... SELECT, values for all columns must be provided in the
VALUES() list or by the SELECT. If you don't know
the order of the columns in the table, use DESCRIBE tbl_name to
find out.
CREATE TABLE Syntax. MySQL always has a default value for all
fields. This is something that is imposed on MySQL to be able to work with
both transactional and not transactional tables. Our view is that checking of
fields content should be done in the application and not in the database
server.
expression may refer to any column that was set earlier in
a value list. For example, you can say this: mysql> INSERT INTO tbl_name (col1,col2) VALUES(15,col1*2);But not this:
mysql> INSERT INTO tbl_name (col1,col2) VALUES(col2*2,15);
LOW_PRIORITY, execution of the
INSERT is delayed until no other clients are reading from the
table. In this case the client has to wait until the insert statement is
completed, which may take a long time if the table is in heavy use. This is in
contrast to INSERT DELAYED, which lets the client continue at
once. See section 6.4.4
INSERT DELAYED Syntax. Note that LOW_PRIORITY
should normally not be used with MyISAM tables as this disables
concurrent inserts. See section 7.1 MyISAM
Tables.
IGNORE in an INSERT
with many value rows, any rows that duplicate an existing PRIMARY
or UNIQUE key in the table are ignored and are not inserted. If
you do not specify IGNORE, the insert is aborted if there is any
row that duplicates an existing key value. You can determine with the C API
function mysql_info() how many rows were inserted into the table.
DONT_USE_DEFAULT_FIELDS
option, INSERT statements generate an error unless you explicitly
specify values for all columns that require a non-NULL value. See
section 2.3.3
Typical configure Options.
AUTO_INCREMENT column with
the mysql_insert_id function. See section 8.4.3.126
mysql_insert_id(). If you use INSERT ... SELECT or an
INSERT ... VALUES statement with multiple value lists, you can use
the C API function mysql_info() to get information about the query.
The format of the information string is shown below:
Records: 100 Duplicates: 0 Warnings: 0
Duplicates indicates the number of rows that couldn't be
inserted because they would duplicate some existing unique index value.
Warnings indicates the number of attempts to insert column values
that were problematic in some way. Warnings can occur under any of the following
conditions:
NULL into a column that has been declared NOT
NULL. The column is set to its default value.
'10.34 a'. The
trailing garbage is stripped and the remaining numeric part is inserted. If
the value doesn't make sense as a number at all, the column is set to
0.
CHAR, VARCHAR,
TEXT, or BLOB column that exceeds the column's
maximum length. The value is truncated to the column's maximum length.
INSERT ... SELECT SyntaxINSERT [LOW_PRIORITY] [IGNORE] [INTO] tbl_name [(column list)] SELECT ...
With INSERT ... SELECT statement you can quickly insert many
rows into a table from one or many tables.
INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;
The following conditions hold for an INSERT ... SELECT
statement:
INSERT statement cannot appear in the
FROM clause of the SELECT part of the query because
it's forbidden in ANSI SQL to SELECT from the same table into
which you are inserting. (The problem is that the SELECT possibly
would find records that were inserted earlier during the same run. When using
sub-select clauses, the situation could easily be very confusing!)
AUTO_INCREMENT columns work as usual.
mysql_info() to get
information about the query. See section 6.4.3
INSERT Syntax.
INSERT
.... SELECT. You can of course also use REPLACE instead of
INSERT to overwrite old rows.
INSERT DELAYED SyntaxINSERT DELAYED ...
The DELAYED option for the INSERT statement is a
MySQL-specific option that is very useful if you have clients that can't wait
for the INSERT to complete. This is a common problem when you use
MySQL for logging and you also periodically run SELECT and
UPDATE statements that take a long time to complete.
DELAYED was introduced in MySQL Version 3.22.15. It is a MySQL
extension to ANSI SQL92.
INSERT DELAYED only works with ISAM and
MyISAM tables. Note that as MyISAM tables supports
concurrent SELECT and INSERT, if there is no free
blocks in the middle of the data file, you very seldom need to use INSERT
DELAYED with MyISAM. See section 7.1 MyISAM
Tables.
When you use INSERT DELAYED, the client will get an OK at once
and the row will be inserted when the table is not in use by any other thread.
Another major benefit of using INSERT DELAYED is that inserts
from many clients are bundled together and written in one block. This is much
faster than doing many separate inserts.
Note that currently the queued rows are only stored in memory until they are
inserted into the table. This means that if you kill mysqld the
hard way (kill -9) or if mysqld dies unexpectedly, any
queued rows that weren't written to disk are lost!
The following describes in detail what happens when you use the
DELAYED option to INSERT or REPLACE. In
this description, the ``thread'' is the thread that received an INSERT
DELAYED command and ``handler'' is the thread that handles all
INSERT DELAYED statements for a particular table.
DELAYED statement for a table, a
handler thread is created to process all DELAYED statements for
the table, if no such handler already exists.
DELAYED lock already; if not, it tells the handler thread to do
so. The DELAYED lock can be obtained even if other threads have a
READ or WRITE lock on the table. However, the
handler will wait for all ALTER TABLE locks or FLUSH
TABLES to ensure that the table structure is up to date.
INSERT statement, but instead of
writing the row to the table, it puts a copy of the final row into a queue
that is managed by the handler thread. Any syntax errors are noticed by the
thread and reported to the client program.
AUTO_INCREMENT value for the resulting row; it can't obtain them
from the server, because the INSERT returns before the insert
operation has been completed. If you use the C API, the
mysql_info() function doesn't return anything meaningful, for the
same reason.
delayed_insert_limit rows are written, the
handler checks whether or not any SELECT statements are still
pending. If so, it allows these to execute before continuing.
INSERT DELAYED commands are received within
delayed_insert_timeout seconds, the handler terminates.
delayed_queue_size rows are pending already in a
specific handler queue, the thread requesting INSERT DELAYED
waits until there is room in the queue. This is done to ensure that the
mysqld server doesn't use all memory for the delayed memory
queue.
delayed_insert in the Command column. It will be
killed if you execute a FLUSH TABLES command or kill it with
KILL thread_id. However, it will first store all queued rows into
the table before exiting. During this time it will not accept any new
INSERT commands from another thread. If you execute an
INSERT DELAYED command after this, a new handler thread will be
created.
INSERT DELAYED commands have
higher priority than normal INSERT commands if there is an
INSERT DELAYED handler already running! Other update commands
will have to wait until the INSERT DELAYED queue is empty,
someone kills the handler thread (with KILL thread_id), or
someone executes FLUSH TABLES.
INSERT
DELAYED commands:
| Variable | Meaning |
Delayed_insert_threads |
Number of handler threads |
Delayed_writes |
Number of rows written with INSERT DELAYED |
Not_flushed_delayed_rows |
Number of rows waiting to be written |
SHOW STATUS statement or by
executing a mysqladmin extended-status command. Note that INSERT DELAYED is slower than a normal INSERT if the
table is not in use. There is also the additional overhead for the server to
handle a separate thread for each table on which you use INSERT
DELAYED. This means that you should only use INSERT DELAYED
when you are really sure you need it!
UPDATE SyntaxUPDATE [LOW_PRIORITY] [IGNORE] tbl_name
SET col_name1=expr1, [col_name2=expr2, ...]
[WHERE where_definition]
[LIMIT #]
UPDATE updates columns in existing table rows with new values.
The SET clause indicates which columns to modify and the values
they should be given. The WHERE clause, if given, specifies which
rows should be updated. Otherwise all rows are updated. If the ORDER
BY clause is specified, the rows will be updated in the order that is
specified.
If you specify the keyword LOW_PRIORITY, execution of the
UPDATE is delayed until no other clients are reading from the
table.
If you specify the keyword IGNORE, the update statement will not
abort even if we get duplicate key errors during the update. Rows that would
cause conflicts will not be updated.
If you access a column from tbl_name in an expression,
UPDATE uses the current value of the column. For example, the
following statement sets the age column to one more than its
current value:
mysql> UPDATE persondata SET age=age+1;
UPDATE assignments are evaluated from left to right. For
example, the following statement doubles the age column, then
increments it:
mysql> UPDATE persondata SET age=age*2, age=age+1;
If you set a column to the value it currently has, MySQL notices this and doesn't update it.
UPDATE returns the number of rows that were
actually changed. In MySQL Version 3.22 or later, the C API function
mysql_info() returns the number of rows that were matched and
updated and the number of warnings that occurred during the UPDATE.
In MySQL Version 3.23, you can use LIMIT # to ensure that only a
given number of rows are changed.
DELETE SyntaxDELETE [LOW_PRIORITY | QUICK] FROM table_name
[WHERE where_definition]
[ORDER BY ...]
[LIMIT rows]
or
DELETE [LOW_PRIORITY | QUICK] table_name[.*] [table_name[.*] ...] FROM
table-references [WHERE where_definition]
DELETE deletes rows from table_name that satisfy
the condition given by where_definition, and returns the number of
records deleted.
If you issue a DELETE with no WHERE clause, all
rows are deleted. If you do this in AUTOCOMMIT mode, this works as
TRUNCATE. See section 6.4.7
TRUNCATE Syntax. In MySQL 3.23 DELETE without a
WHERE clause will return zero as the number of affected records.
If you really want to know how many records are deleted when you are deleting
all rows, and are willing to suffer a speed penalty, you can use a
DELETE statement of this form:
mysql> DELETE FROM table_name WHERE 1>0;
Note that this is much slower than DELETE FROM table_name with
no WHERE clause, because it deletes rows one at a time.
If you specify the keyword LOW_PRIORITY, execution of the
DELETE is delayed until no other clients are reading from the
table.
If you specify the word QUICK then the table handler will not
merge index leafs during delete, which may speed up certain kind of deletes.
In MyISAM tables deleted records are maintained in a linked list and
subsequent INSERT operations reuse old record positions. To reclaim
unused space and reduce file sizes, use the OPTIMIZE TABLE
statement or the myisamchk utility to reorganise tables.
OPTIMIZE TABLE is easier, but myisamchk is faster. See
section 4.5.1
OPTIMIZE TABLE Syntax and section 4.4.6.10
Table Optimisation.
The multi table delete format is supported starting from MySQL 4.0.0.
The idea is that only matching rows from the tables listed
before the FROM clause is deleted. The effect is
that you can delete rows from many tables at the same time and also have
additional tables that are used for searching.
The .* after the table names is there just to be compatible with
Access:
DELETE t1,t2 FROM t1,t2,t3 WHERE t1.id=t2.id AND t2.id=t3.id
In the above case we delete matching rows just from tables t1
and t2.
ORDER BY and using multiple tables in the DELETE is supported in
MySQL 4.0.
If an ORDER BY clause is used, the rows will be deleted in that
order. This is really only useful in conjunction with LIMIT. For
example:
DELETE FROM somelog WHERE user = 'jcole' ORDER BY timestamp LIMIT 1
This will delete the oldest entry (by timestamp) where the row
matches the WHERE clause.
The MySQL-specific LIMIT rows option to DELETE
tells the server the maximum number of rows to be deleted before control is
returned to the client. This can be used to ensure that a specific
DELETE command doesn't take too much time. You can simply repeat
the DELETE command until the number of affected rows is less than
the LIMIT value.
TRUNCATE SyntaxTRUNCATE TABLE table_name
In 3.23 TRUNCATE TABLE is mapped to COMMIT ; DELETE FROM
table_name. See section 6.4.6
DELETE Syntax.
The differences between TRUNCATE TABLE and DELETE FROM
.. are:
TRUNCATE is an Oracle SQL extension.
REPLACE Syntax REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name [(col_name,...)]
VALUES (expression,...),(...),...
or REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name [(col_name,...)]
SELECT ...
or REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name
SET col_name=expression, col_name=expression,...
REPLACE works exactly like INSERT, except that if
an old record in the table has the same value as a new record on a unique index,
the old record is deleted before the new record is inserted. See section 6.4.3
INSERT Syntax.
In other words, you can't access the values of the old row from a
REPLACE statement. In some old MySQL version it looked like you
could do this, but that was a bug that has been corrected.
When one uses a REPLACE command,
mysql_affected_rows() will return 2 if the new row replaced and old
row. This is because in this case one row was inserted and then the duplicate
was deleted.
The above makes it easy to check if REPLACE added or replaced a
row.
LOAD DATA INFILE SyntaxLOAD DATA [LOW_PRIORITY | CONCURRENT] [LOCAL] INFILE 'file_name.txt'
[REPLACE | IGNORE]
INTO TABLE tbl_name
[FIELDS
[TERMINATED BY '\t']
[[OPTIONALLY] ENCLOSED BY '']
[ESCAPED BY '\\' ]
]
[LINES TERMINATED BY '\n']
[IGNORE number LINES]
[(col_name,...)]
The LOAD DATA INFILE statement reads rows from a text file into
a table at a very high speed. If the LOCAL keyword is specified,
the file is read from the client host. If LOCAL is not specified,
the file must be located on the server. (LOCAL is available in
MySQL Version 3.22.6 or later.)
For security reasons, when reading text files located on the server, the
files must either reside in the database directory or be readable by all. Also,
to use LOAD DATA INFILE on server files, you must have the
file privilege on the server host. See section 4.2.6
Privileges Provided by MySQL.
If you specify the keyword LOW_PRIORITY, execution of the
LOAD DATA statement is delayed until no other clients are reading
from the table.
If you specify the keyword CONCURRENT with a MyISAM
table, then other threads can retrieve data from the table while LOAD
DATA is executing. Using this option will of course affect the
performance of LOAD DATA a bit even if no other thread is using the
table at the same time.
Using LOCAL will be a bit slower than letting the server access
the files directly, because the contents of the file must travel from the client
host to the server host. On the other hand, you do not need the
file privilege to load local files.
If you are using MySQL before Version 3.23.24 you can't read from a FIFO with
LOAD DATA INFILE. If you need to read from a FIFO (for example the
output from gunzip), use LOAD DATA LOCAL INFILE instead.
You can also load data files by using the
mysqlimport utility; it operates by sending a LOAD DATA
INFILE command to the server. The --local option causes
mysqlimport to read data files from the client host. You can
specify the --compress option to get better performance over slow
networks if the client and server support the compressed protocol.
When locating files on the server host, the server uses the following rules:
Note that these rules mean a file given as `./myfile.txt' is read
from the server's data directory, whereas a file given as `myfile.txt'
is read from the database directory of the current database. For example, the
following LOAD DATA statement reads the file `data.txt'
from the database directory for db1 because db1 is the
current database, even though the statement explicitly loads the file into a
table in the db2 database:
mysql> USE db1; mysql> LOAD DATA INFILE "data.txt" INTO TABLE db2.my_table;
The REPLACE and IGNORE keywords control handling of
input records that duplicate existing records on unique key values. If you
specify REPLACE, new rows replace existing rows that have the same
unique key value. If you specify IGNORE, input rows that duplicate
an existing row on a unique key value are skipped. If you don't specify either
option, an error occurs when a duplicate key value is found, and the rest of the
text file is ignored.
If you load data from a local file using the LOCAL keyword, the
server has no way to stop transmission of the file in the middle of the
operation, so the default bahavior is the same as if IGNORE is
specified.
If you use LOAD DATA INFILE on an empty MyISAM
table, all non-unique indexes are created in a separate batch (like in
REPAIR). This normally makes LOAD DATA INFILE much
faster when you have many indexes.
LOAD DATA INFILE is the complement of SELECT ... INTO
OUTFILE. See section 6.4.1
SELECT Syntax. To write data from a database to a file, use
SELECT ... INTO OUTFILE. To read the file back into the database,
use LOAD DATA INFILE. The syntax of the FIELDS and
LINES clauses is the same for both commands. Both clauses are
optional, but FIELDS must precede LINES if both are
specified.
If you specify a FIELDS clause, each of its subclauses
(TERMINATED BY, [OPTIONALLY] ENCLOSED BY, and
ESCAPED BY) is also optional, except that you must specify at least
one of them.
If you don't specify a FIELDS clause, the defaults are the same
as if you had written this:
FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\'
If you don't specify a LINES clause, the default is the same as
if you had written this:
LINES TERMINATED BY '\n'
In other words, the defaults cause LOAD DATA INFILE to act as
follows when reading input:
Conversely, the defaults cause SELECT ... INTO OUTFILE to act as
follows when writing output:
Note that to write FIELDS ESCAPED BY '\\', you must specify two
backslashes for the value to be read as a single backslash.
The IGNORE number LINES option can be used to ignore a header of
column names at the start of the file:
mysql> LOAD DATA INFILE "/tmp/file_name" into table test IGNORE 1 LINES;
When you use SELECT ... INTO OUTFILE in tandem with LOAD
DATA INFILE to write data from a database into a file and then read the
file back into the database later, the field and line handling options for both
commands must match. Otherwise, LOAD DATA INFILE will not interpret
the contents of the file properly. Suppose you use SELECT ... INTO
OUTFILE to write a file with fields delimited by commas:
mysql> SELECT * INTO OUTFILE 'data.txt'
FIELDS TERMINATED BY ','
FROM ...;
To read the comma-delimited file back in, the correct statement would be:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2
FIELDS TERMINATED BY ',';
If instead you tried to read in the file with the statement shown below, it
wouldn't work because it instructs LOAD DATA INFILE to look for
tabs between fields:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2
FIELDS TERMINATED BY '\t';
The likely result is that each input line would be interpreted as a single field.
LOAD DATA INFILE can be used to read files obtained from
external sources, too. For example, a file in dBASE format will have fields
separated by commas and enclosed in double quotes. If lines in the file are
terminated by newlines, the command shown below illustrates the field and line
handling options you would use to load the file:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE tbl_name
FIELDS TERMINATED BY ',' ENCLOSED BY '"'
LINES TERMINATED BY '\n';
Any of the field or line handling options may specify an empty string
(''). If not empty, the FIELDS [OPTIONALLY] ENCLOSED
BY and FIELDS ESCAPED BY values must be a single character.
The FIELDS TERMINATED BY and LINES TERMINATED BY
values may be more than one character. For example, to write lines that are
terminated by carriage return-linefeed pairs, or to read a file containing such
lines, specify a LINES TERMINATED BY '\r\n' clause.
For example, to read a file of jokes, that are separated with a line of
%%, into a SQL table you can do:
create table jokes (a int not null auto_increment primary key, joke text not null); load data infile "/tmp/jokes.txt" into table jokes fields terminated by "" lines terminated by "\n%%\n" (joke);
FIELDS [OPTIONALLY] ENCLOSED BY controls quoting of fields. For
output (SELECT ... INTO OUTFILE), if you omit the word
OPTIONALLY, all fields are enclosed by the ENCLOSED BY
character. An example of such output (using a comma as the field delimiter) is
shown below:
"1","a string","100.20" "2","a string containing a , comma","102.20" "3","a string containing a \" quote","102.20" "4","a string containing a \", quote and comma","102.20"
If you specify OPTIONALLY, the ENCLOSED BY
character is used only to enclose CHAR and VARCHAR
fields:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a \" quote",102.20 4,"a string containing a \", quote and comma",102.20
Note that occurrences of the ENCLOSED BY character within a
field value are escaped by prefixing them with the ESCAPED BY
character. Also note that if you specify an empty ESCAPED BY value,
it is possible to generate output that cannot be read properly by LOAD
DATA INFILE. For example, the output just shown above would appear as
shown below if the escape character is empty. Observe that the second field in
the fourth line contains a comma following the quote, which (erroneously)
appears to terminate the field:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a " quote",102.20 4,"a string containing a ", quote and comma",102.20
For input, the ENCLOSED BY character, if present, is stripped
from the ends of field values. (This is true whether or not
OPTIONALLY is specified; OPTIONALLY has no effect on
input interpretation.) Occurrences of the ENCLOSED BY character
preceded by the ESCAPED BY character are interpreted as part of the
current field value. In addition, duplicated ENCLOSED BY characters
occurring within fields are interpreted as single ENCLOSED BY
characters if the field itself starts with that character. For example, if
ENCLOSED BY '"' is specified, quotes are handled as shown below:
"The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss The ""BIG"" boss -> The ""BIG"" boss
FIELDS ESCAPED BY controls how to write or read special
characters. If the FIELDS ESCAPED BY character is not empty, it is
used to prefix the following characters on output:
FIELDS ESCAPED BY character
FIELDS [OPTIONALLY] ENCLOSED BY character
FIELDS TERMINATED BY and
LINES TERMINATED BY values
0 (what is actually written following the escape
character is ASCII '0', not a zero-valued byte) If the FIELDS ESCAPED BY character is empty, no characters are
escaped. It is probably not a good idea to specify an empty escape character,
particularly if field values in your data contain any of the characters in the
list just given.
For input, if the FIELDS ESCAPED BY character is not empty,
occurrences of that character are stripped and the following character is taken
literally as part of a field value. The exceptions are an escaped
`0' or `N' (for example, \0 or
\N if the escape character is `\'). These sequences
are interpreted as ASCII 0 (a zero-valued byte) and
NULL. See below for the rules on NULL handling.
For more information about `\'-escape syntax, see section 6.1.1 Literals: How to Write Strings and Numbers.
In certain cases, field and line handling options interact:
LINES TERMINATED BY is an empty string and FIELDS
TERMINATED BY is non-empty, lines are also terminated with FIELDS
TERMINATED BY.
FIELDS TERMINATED BY and FIELDS ENCLOSED
BY values are both empty (''), a fixed-row (non-delimited)
format is used. With fixed-row format, no delimiters are used between fields.
Instead, column values are written and read using the ``display'' widths of
the columns. For example, if a column is declared as INT(7),
values for the column are written using 7-character fields. On input, values
for the column are obtained by reading 7 characters. Fixed-row format also
affects handling of NULL values; see below. Note that fixed-size
format will not work if you are using a multi-byte character set. Handling of NULL values varies, depending on the
FIELDS and LINES options you use:
FIELDS and LINES values,
NULL is written as \N for output and \N
is read as NULL for input (assuming the ESCAPED BY
character is `\').
FIELDS ENCLOSED BY is not empty, a field containing the
literal word NULL as its value is read as a NULL
value (this differs from the word NULL enclosed within
FIELDS ENCLOSED BY characters, which is read as the string
'NULL').
FIELDS ESCAPED BY is empty, NULL is written
as the word NULL.
FIELDS TERMINATED
BY and FIELDS ENCLOSED BY are both empty),
NULL is written as an empty string. Note that this causes both
NULL values and empty strings in the table to be
indistinguishable when written to the file because they are both written as
empty strings. If you need to be able to tell the two apart when reading the
file back in, you should not use fixed-row format. Some cases are not supported by LOAD DATA INFILE:
FIELDS TERMINATED BY and FIELDS
ENCLOSED BY both empty) and BLOB or TEXT
columns.
LOAD DATA INFILE won't be able to interpret the input properly.
For example, the following FIELDS clause would cause problems: FIELDS TERMINATED BY '"' ENCLOSED BY '"'
FIELDS ESCAPED BY is empty, a field value that contains an
occurrence of FIELDS ENCLOSED BY or LINES TERMINATED
BY followed by the FIELDS TERMINATED BY value will cause
LOAD DATA INFILE to stop reading a field or line too early. This
happens because LOAD DATA INFILE cannot properly determine where
the field or line value ends. The following example loads all columns of the persondata table:
mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata;
No field list is specified, so LOAD DATA INFILE expects input
rows to contain a field for each table column. The default FIELDS
and LINES values are used.
If you wish to load only some of a table's columns, specify a field list:
mysql> LOAD DATA INFILE 'persondata.txt'
INTO TABLE persondata (col1,col2,...);
You must also specify a field list if the order of the fields in the input file differs from the order of the columns in the table. Otherwise, MySQL cannot tell how to match up input fields with table columns.
If a row has too few fields, the columns for which no input field is present
are set to default values. Default value assignment is described in section 6.5.3
CREATE TABLE Syntax.
An empty field value is interpreted differently than if the field value is missing:
0.
Note that these are the same values that result if you assign an empty string
explicitly to a string, numeric, or date or time type explicitly in an
INSERT or UPDATE statement.
TIMESTAMP columns are only set to the current date and time if
there is a NULL value for the column, or (for the first
TIMESTAMP column only) if the TIMESTAMP column is left
out from the field list when a field list is specified.
If an input row has too many fields, the extra fields are ignored and the number of warnings is incremented.
LOAD DATA INFILE regards all input as strings, so you can't use
numeric values for ENUM or SET columns the way you can
with INSERT statements. All ENUM and SET
values must be specified as strings!
If you are using the C API, you can get information about
the query by calling the API function mysql_info() when the
LOAD DATA INFILE query finishes. The format of the information
string is shown below:
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
Warnings occur under the same circumstances as when values are inserted via
the INSERT statement (see section 6.4.3
INSERT Syntax), except that LOAD DATA INFILE also
generates warnings when there are too few or too many fields in the input row.
The warnings are not stored anywhere; the number of warnings can only be used as
an indication if everything went well. If you get warnings and want to know
exactly why you got them, one way to do this is to use SELECT ... INTO
OUTFILE into another file and compare this to your original input file.
If you need LOAD DATA to read from a pipe, you can use the
following trick:
mkfifo /mysql/db/x/x chmod 666 /mysql/db/x/x cat < /dev/tcp/10.1.1.12/4711 > /nt/mysql/db/x/x mysql -e "LOAD DATA INFILE 'x' INTO TABLE x" x
If you are using a version of MySQL older than 3.23.25 you can only do the
above with LOAD DATA LOCAL INFILE.
For more information about the efficiency of INSERT versus
LOAD DATA INFILE and speeding up LOAD DATA INFILE, See
section 5.2.8
Speed of INSERT Queries.
DO SyntaxDO expression, [expression, ...]
Execute the expression but don't return any results. This is a shorthand of
SELECT expression, expression, but has the advantage that it's
slightly faster when you don't care about the result.
This is mainly useful with functions that has side effects, like
RELEASE_LOCK.
CREATE,
DROP, ALTERCREATE DATABASE SyntaxCREATE DATABASE [IF NOT EXISTS] db_name
CREATE DATABASE creates a database with the given name. Rules
for allowable database names are given in section 6.1.2
Database, Table, Index, Column, and Alias Names. An error occurs if the
database already exists and you didn't specify IF NOT EXISTS.
Databases in MySQL are implemented as directories containing files that
correspond to tables in the database. Because there are no tables in a database
when it is initially created, the CREATE DATABASE statement only
creates a directory under the MySQL data directory.
You can also create databases with
mysqladmin. See section 4.8
MySQL Client-Side Scripts and Utilities.
DROP DATABASE SyntaxDROP DATABASE [IF EXISTS] db_name
DROP DATABASE drops all tables in the database and deletes the
database. If you do a DROP DATABASE on a symbolic linked database,
both the link and the original database is deleted. Be VERY careful with
this command!
DROP DATABASE returns the number of files that were removed from
the database directory. Normally, this is three times the number of tables,
because normally each table corresponds to a `.MYD' file, a
`.MYI' file, and a `.frm' file.
The DROP DATABASE command removes from the given database
directory all files with the following extensions:
| Ext | Ext | Ext | Ext |
| .BAK | .DAT | .HSH | .ISD |
| .ISM | .ISM | .MRG | .MYD |
| .MYI | .db | .frm |
All subdirectories that consists of 2 digits (RAID directories)
are also removed.
In MySQL Version 3.22 or later, you can use the keywords IF
EXISTS to prevent an error from occurring if the database doesn't exist.
You can also drop databases with mysqladmin.
See section 4.8
MySQL Client-Side Scripts and Utilities.
CREATE TABLE SyntaxCREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)]
[table_options] [select_statement]
create_definition:
col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT]
[PRIMARY KEY] [reference_definition]
or PRIMARY KEY (index_col_name,...)
or KEY [index_name] (index_col_name,...)
or INDEX [index_name] (index_col_name,...)
or UNIQUE [INDEX] [index_name] (index_col_name,...)
or FULLTEXT [INDEX] [index_name] (index_col_name,...)
or [CONSTRAINT symbol] FOREIGN KEY [index_name] (index_col_name,...)
[reference_definition]
or CHECK (expr)
type:
TINYINT[(length)] [UNSIGNED] [ZEROFILL]
or SMALLINT[(length)] [UNSIGNED] [ZEROFILL]
or MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL]
or INT[(length)] [UNSIGNED] [ZEROFILL]
or INTEGER[(length)] [UNSIGNED] [ZEROFILL]
or BIGINT[(length)] [UNSIGNED] [ZEROFILL]
or REAL[(length,decimals)] [UNSIGNED] [ZEROFILL]
or DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL]
or FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL]
or DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL]
or NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL]
or CHAR(length) [BINARY]
or VARCHAR(length) [BINARY]
or DATE
or TIME
or TIMESTAMP
or DATETIME
or TINYBLOB
or BLOB
or MEDIUMBLOB
or LONGBLOB
or TINYTEXT
or TEXT
or MEDIUMTEXT
or LONGTEXT
or ENUM(value1,value2,value3,...)
or SET(value1,value2,value3,...)
index_col_name:
col_name [(length)]
reference_definition:
REFERENCES tbl_name [(index_col_name,...)]
[MATCH FULL | MATCH PARTIAL]
[ON DELETE reference_option]
[ON UPDATE reference_option]
reference_option:
RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT
table_options:
TYPE = {BDB | HEAP | ISAM | InnoDB | MERGE | MRG_MYISAM | MYISAM }
or AUTO_INCREMENT = #
or AVG_ROW_LENGTH = #
or CHECKSUM = {0 | 1}
or COMMENT = "string"
or MAX_ROWS = #
or MIN_ROWS = #
or PACK_KEYS = {0 | 1 | DEFAULT}
or PASSWORD = "string"
or DELAY_KEY_WRITE = {0 | 1}
or ROW_FORMAT= { default | dynamic | fixed | compressed }
or RAID_TYPE= {1 | STRIPED | RAID0 } RAID_CHUNKS=# RAID_CHUNKSIZE=#
or UNION = (table_name,[table_name...])
or INSERT_METHOD= {NO | FIRST | LAST }
or DATA DIRECTORY="absolute path to directory"
or INDEX DIRECTORY="absolute path to directory"
select_statement:
[IGNORE | REPLACE] SELECT ... (Some legal select statement)
CREATE TABLE creates a table with the given name in the current
database. Rules for allowable table names are given in section 6.1.2
Database, Table, Index, Column, and Alias Names. An error occurs if there is
no current database or if the table already exists.
In MySQL Version 3.22 or later, the table name can be specified as
db_name.tbl_name. This works whether or not there is a current
database.
In MySQL Version 3.23, you can use the TEMPORARY keyword when
you create a table. A temporary table will automatically be deleted if a
connection dies and the name is per connection. This means that two different
connections can both use the same temporary table name without conflicting with
each other or with an existing table of the same name. (The existing table is
hidden until the temporary table is deleted.)
In MySQL Version 3.23 or later, you can use the keywords IF NOT
EXISTS so that an error does not occur if the table already exists. Note
that there is no verification that the table structures are identical.
Each table tbl_name is represented by some files in the database
directory. In the case of MyISAM-type tables you will get:
| File | Purpose |
tbl_name.frm |
Table definition (form) file |
tbl_name.MYD |
Data file |
tbl_name.MYI |
Index file |
For more information on the properties of the various column types, see section 6.2 Column Types:
NULL nor NOT NULL is specified, the
column is treated as though NULL had been specified.
AUTO_INCREMENT. When you insert a value of NULL
(recommended) or 0 into an AUTO_INCREMENT column,
the column is set to value+1, where value is the
largest value for the column currently in the table.
AUTO_INCREMENT sequences begin with 1. See section
8.4.3.126
mysql_insert_id(). If you delete the row containing the
maximum value for an AUTO_INCREMENT column, the value will be
reused with an ISAM, or BDB table but not with a
MyISAM or InnoDB table. If you delete all rows in
the table with DELETE FROM table_name (without a
WHERE) in AUTOCOMMIT mode, the sequence starts over
for all table types. NOTE: There can be only one
AUTO_INCREMENT column per table, and it must be indexed. MySQL
Version 3.23 will also only work properly if the auto_increment column only
has positive values. Inserting a negative number is regarded as inserting a
very large positive number. This is done to avoid precision problems when
numbers 'wrap' over from positive to negative and also to ensure that one
doesn't accidentally get an auto_increment column that contains 0. In MyISAM
and BDB tables you can specify AUTO_INCREMENT secondary column in
a multi-column key. See section 3.5.9
Using AUTO_INCREMENT. To make
MySQL compatible with some ODBC applications, you can find the last inserted
row with the following query: SELECT * FROM tbl_name WHERE auto_col IS NULL
NULL values are handled differently for
TIMESTAMP columns than for other column types. You cannot store a
literal NULL in a TIMESTAMP column; setting the
column to NULL sets it to the current date and time. Because
TIMESTAMP columns behave this way, the NULL and
NOT NULL attributes do not apply in the normal way and are
ignored if you specify them. On the other hand, to make it easier for MySQL
clients to use TIMESTAMP columns, the server reports that such
columns may be assigned NULL values (which is true), even though
TIMESTAMP never actually will contain a NULL value.
You can see this when you use DESCRIBE tbl_name to get a
description of your table. Note that setting a TIMESTAMP column
to 0 is not the same as setting it to NULL, because
0 is a valid TIMESTAMP value.
DEFAULT value is specified for a
column, MySQL automatically assigns one. If the column may take
NULL as a value, the default value is NULL. If the
column is declared as NOT NULL, the default value depends on the
column type:
AUTO_INCREMENT attribute, the default is 0. For an
AUTO_INCREMENT column, the default value is the next value in
the sequence.
TIMESTAMP, the default
is the appropriate zero value for the type. For the first
TIMESTAMP column in a table, the default value is the current
date and time. See section 6.2.2
Date and Time Types.
ENUM, the default value is the
empty string. For ENUM, the default is the first enumeration
value (if you haven't explicitely specified another default value with the
DEFAULT directive). NOW() or
CURRENT_DATE.
KEY is a synonym for INDEX.
UNIQUE key can have only distinct values. An
error occurs if you try to add a new row with a key that matches an existing
row.
PRIMARY KEY is a unique
KEY with the extra constraint that all key columns must be
defined as NOT NULL. In MySQL the key is named
PRIMARY. A table can have only one PRIMARY KEY. If
you don't have a PRIMARY KEY and some applications ask for the
PRIMARY KEY in your tables, MySQL will return the first
UNIQUE key, which doesn't have any NULL columns, as
the PRIMARY KEY.
PRIMARY KEY can be a multiple-column index. However, you
cannot create a multiple-column index using the PRIMARY KEY key
attibute in a column specification. Doing so will mark only that single column
as primary. You must use the PRIMARY KEY(index_col_name, ...)
syntax.
PRIMARY or UNIQUE key consists of only
one column and this is of type integer, you can also refer to it as
_rowid (new in Version 3.23.11).
index_col_name, with an optional suffix
(_2, _3, ...) to make it unique. You
can see index names for a table using SHOW INDEX FROM tbl_name.
See section 4.5.6
SHOW Syntax.
MyISAM table
type supports indexes on columns that can have NULL values. In
other cases you must declare such columns NOT NULL or an error
results.
col_name(length) syntax, you can specify an index that
uses only a part of a CHAR or VARCHAR column. This
can make the index file much smaller. See section 5.4.4
Column Indexes.
MyISAM table type supports indexing on
BLOB and TEXT columns. When putting an index on a
BLOB or TEXT column you MUST always specify the
length of the index: CREATE TABLE test (blob_col BLOB, index(blob_col(10)));
ORDER BY or GROUP BY with a
TEXT or BLOB column, only the first
max_sort_length bytes are used. See section 6.2.3.2 The
BLOB and TEXT Types.
MyISAM table type supports FULLTEXT indexes.
They can be created only from VARCHAR and TEXT
columns. Indexing always happens over the entire column, partial indexing is
not supported. See section 6.8
MySQL Full-text Search for details of operation.
FOREIGN KEY, CHECK, and
REFERENCES clauses don't actually do anything. The syntax for
them is provided only for compatibility, to make it easier to port code from
other SQL servers and to run applications that create tables with references.
See section 1.7.4
MySQL Differences Compared to ANSI SQL92.
NULL column takes one bit extra, rounded up to the
nearest byte.
row length = 1
+ (sum of column lengths)
+ (number of NULL columns + 7)/8
+ (number of variable-length columns)
table_options and SELECT options are only
implemented in MySQL Version 3.23 and above. The different table types are:
| Table type | Description |
| BDB or Berkeley_db | Transaction-safe tables with page locking. See section 7.6 BDB or Berkeley_DB Tables. |
| HEAP | The data for this table is only stored in memory. See section 7.4 HEAP Tables. |
| ISAM | The original table handler. See section 7.3 ISAM Tables. |
| InnoDB | Transaction-safe tables with row locking. See section 7.5 InnoDB Tables. |
| MERGE | A collection of MyISAM tables used as one table. See section 7.2 MERGE Tables. |
| MRG_MyISAM | An alias for MERGE tables |
| MyISAM | The new binary portable table handler that is replacing ISAM. See section 7.1 MyISAM Tables. |
TYPE=BDB is specified, and that
distribution of MySQL does not support BDB tables, the table will
be created as MyISAM instead. The other table options are used to
optimise the behavior of the table. In most cases, you don't have to specify
any of them. The options work for all table types, if not otherwise indicated:
| Option | Description |
AUTO_INCREMENT |
The next auto_increment value you want to set for your table (MyISAM). |
AVG_ROW_LENGTH |
An approximation of the average row length for your table. You only need to set this for large tables with variable size records. |
CHECKSUM |
Set this to 1 if you want MySQL to maintain a checksum for all rows (makes the table a little slower to update but makes it easier to find corrupted tables) (MyISAM). |
COMMENT |
A 60-character comment for your table. |
MAX_ROWS |
Max number of rows you plan to store in the table. |
MIN_ROWS |
Minimum number of rows you plan to store in the table. |
PACK_KEYS |
Set this to 1 if you want to have a smaller index. This usually
makes updates slower and reads faster (MyISAM, ISAM). Setting this to 0
will disable all packing of keys. Setting this to DEFAULT
(MySQL 4.0) will tell the table handler to only pack long
CHAR/VARCHAR columns. |
PASSWORD |
Encrypt the .frm file with a password. This option
doesn't do anything in the standard MySQL version. |
DELAY_KEY_WRITE |
Set this to 1 if want to delay key table updates until the table is closed (MyISAM). |
ROW_FORMAT |
Defines how the rows should be stored. Currently this option only
works with MyISAM tables, which supports the DYNAMIC and
FIXED row formats. See section 7.1.2
MyISAM Table Formats. |
MyISAM table, MySQL uses the product of max_rows *
avg_row_length to decide how big the resulting table will be. If you
don't specify any of the above options, the maximum size for a table will be
4G (or 2G if your operating systems only supports 2G tables). The reason for
this is just to keep down the pointer sizes to make the index smaller and
faster if you don't really need big files. If you don't use
PACK_KEYS, the default is to only pack strings, not numbers. If
you use PACK_KEYS=1, numbers will be packed as well. When packing
binary number keys, MySQL will use prefix compression. This means that you
will only get a big benefit of this if you have many numbers that are the
same. Prefix compression means that every key needs one extra byte to indicate
how many bytes of the previous key are the same for the next key (note that
the pointer to the row is stored in high-byte-first-order directly after the
key, to improve compression). This means that if you have many equal keys on
two rows in a row, all following 'same' keys will usually only take 2 bytes
(including the pointer to the row). Compare this to the ordinary case where
the following keys will take storage_size_for_key + pointer_size (usually 4).
On the other hand, if all keys are totally different, you will lose 1 byte per
key, if the key isn't a key that can have NULL values. (In this
case the packed key length will be stored in the same byte that is used to
mark if a key is NULL.)
SELECT after the CREATE
statement, MySQL will create new fields for all elements in the
SELECT. For example: mysql> CREATE TABLE test (a int not null auto_increment,
primary key (a), key(b))
TYPE=MyISAM SELECT b,c from test2;
This will create a MyISAM table with three columns, a, b,
and c. Notice that the columns from the SELECT statement are
appended to the right side of the table, not overlapped onto it. Take the
following example: mysql> select * from foo; +---+ | n | +---+ | 1 | +---+ mysql> create table bar (m int) select n from foo; Query OK, 1 row affected (0.02 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> select * from bar; +------+---+ | m | n | +------+---+ | NULL | 1 | +------+---+ 1 row in set (0.00 sec)For each row in table
foo, a row is inserted in
bar with the values from foo and default values for
the new columns. CREATE TABLE ... SELECT will not automatically
create any indexes for you. This is done intentionally to make the command as
flexible as possible. If you want to have indexes in the created table, you
should specify these before the SELECT statement: mysql> create table bar (unique (n)) select n from foo;If any errors occur while copying the data to the table, it will automatically be deleted. To ensure that the update log/binary log can be used to re-create the original tables, MySQL will not allow concurrent inserts during
CREATE TABLE .... SELECT.
RAID_TYPE option will help you to break the 2G/4G limit
for the MyISAM data file (not the index file) on operating systems that don't
support big files. You can get more speed from the I/O bottleneck by putting
RAID directories on different physical disks.
RAID_TYPE will work on any OS, as long as you have configured
MySQL with --with-raid. For now the only allowed
RAID_TYPE is STRIPED (1 and
RAID0 are aliases for this). If you specify
RAID_TYPE=STRIPED for a MyISAM table,
MyISAM will create RAID_CHUNKS subdirectories named
00, 01, 02 in the database directory. In each of these directories
MyISAM will create a table_name.MYD. When writing
data to the data file, the RAID handler will map the first
RAID_CHUNKSIZE *1024 bytes to the first file, the next
RAID_CHUNKSIZE *1024 bytes to the next file and so on.
UNION is used when you want to use a collection of identical
tables as one. This only works with MERGE tables. See section 7.2 MERGE
Tables. For the moment you need to have SELECT,
UPDATE, and DELETE privileges on the tables you map
to a MERGE table. All mapped tables must be in the same database
as the MERGE table.
MERGE table, you have to
specify with INSERT_METHOD into with table the row should be
inserted. See section 7.2 MERGE
Tables. This option was introduced in MySQL 4.0.0.
PRIMARY key will be placed first,
followed by all UNIQUE keys and then the normal keys. This helps
the MySQL optimiser to prioritise which key to use and also more quickly
detect duplicated UNIQUE keys.
DATA DIRECTORY="directory" or INDEX
DIRECTORY="directory" you can specify where the table handler should
put it's table and index files. Note that the directory should be a full path
to the directory (not relative path). This only works for MyISAM
tables in MySQL 4.0, when you are not using the
--skip-symlink option. See section 5.6.1.2
Using Symbolic Links for Tables. In some cases, MySQL silently changes a column specification from that given
in a CREATE TABLE statement. (This may also occur with ALTER
TABLE.):
VARCHAR columns with a length less than four are changed to
CHAR.
VARCHAR, TEXT, or
BLOB), all CHAR columns longer than three characters
are changed to VARCHAR columns. This doesn't affect how you use
the columns in any way; in MySQL, VARCHAR is just a different way
to store characters. MySQL performs this conversion because it saves space and
makes table operations faster. See section 7
MySQL Table Types.
TIMESTAMP display sizes must be even and in the range from 2
to 14. If you specify a display size of 0 or greater than 14, the size is
coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the
next higher even number.
NULL in a TIMESTAMP
column; setting it to NULL sets it to the current date and time.
Because TIMESTAMP columns behave this way, the NULL
and NOT NULL attributes do not apply in the normal way and are
ignored if you specify them. DESCRIBE tbl_name always reports
that a TIMESTAMP column may be assigned NULL values.
If you want to see whether or not MySQL used a column type other than the one
you specified, issue a DESCRIBE tbl_name statement after creating
or altering your table.
Certain other column type changes may occur if you
compress a table using myisampack. See section 7.1.2.3
Compressed Table Characteristics.
ALTER TABLE SyntaxALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...]
alter_specification:
ADD [COLUMN] create_definition [FIRST | AFTER column_name ]
or ADD [COLUMN] (create_definition, create_definition,...)
or ADD INDEX [index_name] (index_col_name,...)
or ADD PRIMARY KEY (index_col_name,...)
or ADD UNIQUE [index_name] (index_col_name,...)
or ADD FULLTEXT [index_name] (index_col_name,...)
or ADD [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...)
[reference_definition]
or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
or CHANGE [COLUMN] old_col_name create_definition [FIRST | AFTER column_name]
or MODIFY [COLUMN] create_definition [FIRST | AFTER column_name]
or DROP [COLUMN] col_name
or DROP PRIMARY KEY
or DROP INDEX index_name
or DISABLE KEYS
or ENABLE KEYS
or RENAME [TO] new_tbl_name
or ORDER BY col
or table_options
ALTER TABLE allows you to change the structure of an existing
table. For example, you can add or delete columns, create or destroy indexes,
change the type of existing columns, or rename columns or the table itself. You
can also change the comment for the table and type of the table. See section 6.5.3
CREATE TABLE Syntax.
If you use ALTER TABLE to change a column specification but
DESCRIBE tbl_name indicates that your column was not changed, it is
possible that MySQL ignored your modification for one of the reasons described
in section 6.5.3.1
Silent Column Specification Changes. For example, if you try to change a
VARCHAR column to CHAR, MySQL will still use
VARCHAR if the table contains other variable-length columns.
ALTER TABLE works by making a temporary copy of the original
table. The alteration is performed on the copy, then the original table is
deleted and the new one is renamed. This is done in such a way that all updates
are automatically redirected to the new table without any failed updates. While
ALTER TABLE is executing, the original table is readable by other
clients. Updates and writes to the table are stalled until the new table is
ready.
Note that if you use any other option to ALTER TABLE than
RENAME, MySQL will always create a temporary table, even if the
data wouldn't strictly need to be copied (like when you change the name of a
column). We plan to fix this in the future, but as one doesn't normally do
ALTER TABLE that often this isn't that high on our TODO.
ALTER TABLE, you need ALTER,
INSERT, and CREATE privileges on the table.
IGNORE is a MySQL extension to ANSI SQL92. It controls how
ALTER TABLE works if there are duplicates on unique keys in the
new table. If IGNORE isn't specified, the copy is aborted and
rolled back. If IGNORE is specified, then for rows with
duplicates on a unique key, only the first row is used; the others are
deleted.
ADD, ALTER,
DROP, and CHANGE clauses in a single ALTER
TABLE statement. This is a MySQL extension to ANSI SQL92, which allows
only one of each clause per ALTER TABLE statement.
CHANGE col_name, DROP col_name, and DROP
INDEX are MySQL extensions to ANSI SQL92.
MODIFY is an Oracle extension to ALTER TABLE.
COLUMN is a pure noise word and can be
omitted.
ALTER TABLE tbl_name RENAME TO new_name without
any other options, MySQL simply renames the files that correspond to the table
tbl_name. There is no need to create the temporary table. See
section 6.5.5
RENAME TABLE Syntax.
create_definition clauses use the same syntax for
ADD and CHANGE as for CREATE TABLE.
Note that this syntax includes the column name, not just the column type. See
section 6.5.3
CREATE TABLE Syntax.
CHANGE old_col_name
create_definition clause. To do so, specify the old and new column
names and the type that the column currently has. For example, to rename an
INTEGER column from a to b, you can do
this: mysql> ALTER TABLE t1 CHANGE a b INTEGER;If you want to change a column's type but not the name,
CHANGE syntax still requires two column names even if they are
the same. For example: mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL;However, as of MySQL Version 3.22.16a, you can also use
MODIFY to change a column's type without renaming it: mysql> ALTER TABLE t1 MODIFY b BIGINT NOT NULL;
CHANGE or MODIFY to shorten a column
for which an index exists on part of the column (for instance, if you have an
index on the first 10 characters of a VARCHAR column), you cannot
make the column shorter than the number of characters that are indexed.
CHANGE or
MODIFY, MySQL tries to convert data to the new type as well as
possible.
FIRST or
ADD ... AFTER col_name to add a column at a specific position
within a table row. The default is to add the column last.
ALTER COLUMN specifies a new default value for a column or
removes the old default value. If the old default is removed and the column
can be NULL, the new default is NULL. If the column
cannot be NULL, MySQL assigns a default value, as described in
section 6.5.3
CREATE TABLE Syntax.
DROP INDEX removes an index. This is a MySQL extension to
ANSI SQL92. See section 6.5.8
DROP INDEX Syntax.
DROP TABLE instead.
DROP PRIMARY KEY drops the primary index. If no such index
exists, it drops the first UNIQUE index in the table. (MySQL
marks the first UNIQUE key as the PRIMARY KEY if no
PRIMARY KEY was specified explicitly.) If you add a UNIQUE INDEX or PRIMARY
KEY to a table, this is stored before any not UNIQUE index
so that MySQL can detect duplicate keys as early as possible.
ORDER BY allows you to create the new table with the rows in
a specific order. Note that the table will not remain in this order after
inserts and deletes. In some cases, it may make sorting easier for MySQL if
the table is in order by the column that you wish to order it by later. This
option is mainly useful when you know that you are mostly going to query the
rows in a certain order; By using this option after big changes to the table,
you may be able to get higher performance.
ALTER TABLE on a MyISAM table, all
non-unique indexes are created in a separate batch (like in
REPAIR). This should make ALTER TABLE much faster
when you have many indexes.
ALTER TABLE ... DISABLE KEYS makes MySQL to stop
updating non-unique indexes for MyISAM table. ALTER TABLE
... ENABLE KEYS then should be used to recreate missing indexes. As
MySQL does it with special algorithm which is much faster then inserting keys
one by one, disabling keys could give a considerable speedup on bulk inserts.
mysql_info(), you
can find out how many records were copied, and (when IGNORE is
used) how many records were deleted due to duplication of unique key values.
FOREIGN KEY,
CHECK, and REFERENCES clauses don't actually do
anything. The syntax for them is provided only for compatibility, to make it
easier to port code from other SQL servers and to run applications that create
tables with references. See section 1.7.4
MySQL Differences Compared to ANSI SQL92. Here is an example that shows some of the uses of ALTER TABLE.
We begin with a table t1 that is created as shown below:
mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10));
To rename the table from t1 to t2:
mysql> ALTER TABLE t1 RENAME t2;
To change column a from INTEGER to TINYINT
NOT NULL (leaving the name the same), and to change column b
from CHAR(10) to CHAR(20) as well as renaming it from
b to c:
mysql> ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20);
To add a new TIMESTAMP column named d:
mysql> ALTER TABLE t2 ADD d TIMESTAMP;
To add an index on column d, and make column a the
primary key:
mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a);
To remove column c:
mysql> ALTER TABLE t2 DROP COLUMN c;
To add a new AUTO_INCREMENT integer column named c:
mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT,
ADD INDEX (c);
Note that we indexed c, because AUTO_INCREMENT
columns must be indexed, and also that we declare c as NOT
NULL, because indexed columns cannot be NULL.
When you add an AUTO_INCREMENT column, column values are filled
in with sequence numbers for you automatically. You can set the first sequence
number by executing SET INSERT_ID=# before ALTER TABLE
or using the AUTO_INCREMENT = # table option. See section 5.5.6
SET Syntax.
With MyISAM tables, if you don't change the AUTO_INCREMENT
column, the sequence number will not be affected. If you drop an
AUTO_INCREMENT column and then add another
AUTO_INCREMENT column, the numbers will start from 1 again.
See section A.6.1
Problems with ALTER TABLE..
RENAME TABLE SyntaxRENAME TABLE tbl_name TO new_table_name[, tbl_name2 TO new_table_name2,...]
The rename is done atomically, which means that no other thread can access any of the tables while the rename is running. This makes it possible to replace a table with an empty one:
CREATE TABLE new_table (...); RENAME TABLE old_table TO backup_table, new_table TO old_table;
The rename is done from left to right, which means that if you want to swap two tables names, you have to:
RENAME TABLE old_table TO backup_table,
new_table TO old_table,
backup_table TO new_table;
As long as two databases are on the same disk you can also rename from one database to another:
RENAME TABLE current_database.table_name TO other_database.table_name;
When you execute RENAME, you can't have any locked tables or
active transactions. You must also have the ALTER and
DROP privilege on the original table and CREATE and
INSERT privilege on the new table.
If MySQL encounters any errors in a multiple table rename, it will do a reverse rename for all renamed tables to get everything back to the original state.
DROP TABLE SyntaxDROP TABLE [IF EXISTS] tbl_name [, tbl_name,...] [RESTRICT | CASCADE]
DROP TABLE removes one or more tables. All table data and the
table definition are removed, so be careful with this
command!
In MySQL Version 3.22 or later, you can use the keywords IF
EXISTS to prevent an error from occurring for tables that don't exist.
RESTRICT and CASCADE are allowed to make porting
easier. For the moment they don't do anything.
Note: DROP TABLE is not transaction-safe and
will automatically commit any active transactions.
CREATE INDEX SyntaxCREATE [UNIQUE|FULLTEXT] INDEX index_name ON tbl_name (col_name[(length)],... )
The CREATE INDEX statement doesn't do anything in MySQL prior to
Version 3.22. In Version 3.22 or later, CREATE INDEX is mapped to
an ALTER TABLE statement to create indexes. See section 6.5.4
ALTER TABLE Syntax.
Normally, you create all indexes on a table at the time the table itself is
created with CREATE TABLE. See section 6.5.3
CREATE TABLE Syntax. CREATE INDEX allows you to
add indexes to existing tables.
A column list of the form (col1,col2,...) creates a
multiple-column index. Index values are formed by concatenating the values of
the given columns.
For CHAR and VARCHAR columns, indexes can be
created that use only part of a column, using col_name(length)
syntax. (On BLOB and TEXT columns the length is
required.) The statement shown below creates an index using the first 10
characters of the name column:
mysql> CREATE INDEX part_of_name ON customer (name(10));
Because most names usually differ in the first 10 characters, this index
should not be much slower than an index created from the entire
name column. Also, using partial columns for indexes can make the
index file much smaller, which could save a lot of disk space and might also
speed up INSERT operations!
Note that you can only add an index on a column that can have
NULL values or on a BLOB/TEXT column if
you are using MySQL Version 3.23.2 or newer and are using the
MyISAM table type.
For more information about how MySQL uses indexes, see section 5.4.3 How MySQL Uses Indexes.
FULLTEXT indexes can index only VARCHAR and
TEXT columns, and only in MyISAM tables.
FULLTEXT indexes are available in MySQL Version 3.23.23 and later.
section 6.8
MySQL Full-text Search.
DROP INDEX SyntaxDROP INDEX index_name ON tbl_name
DROP INDEX drops the index named index_name from
the table tbl_name. DROP INDEX doesn't do anything in
MySQL prior to Version 3.22. In Version 3.22 or later, DROP INDEX
is mapped to an ALTER TABLE statement to drop the index. See
section 6.5.4
ALTER TABLE Syntax.
USE SyntaxUSE db_name
The USE db_name statement tells MySQL to use the
db_name database as the default database for subsequent queries.
The database remains current until the end of the session or until another
USE statement is issued:
mysql> USE db1; mysql> SELECT count(*) FROM mytable; # selects from db1.mytable mysql> USE db2; mysql> SELECT count(*) FROM mytable; # selects from db2.mytable
Making a particular database current by means of the USE
statement does not preclude you from accessing tables in other databases. The
example below accesses the author table from the db1
database and the editor table from the db2 database:
mysql> USE db1;
mysql> SELECT author_name,editor_name FROM author,db2.editor
WHERE author.editor_id = db2.editor.editor_id;
The USE statement is
provided for Sybase compatibility.
DESCRIBE Syntax (Get Information About
Columns){DESCRIBE | DESC} tbl_name {col_name | wild}
DESCRIBE is a shortcut for SHOW COLUMNS FROM. See
section 4.5.6.1
Retrieving information about Database, Tables, Columns, and Indexes.
DESCRIBE provides information about a table's columns.
col_name may be a column name or a string containing the SQL
`%' and `_' wild-card characters.
If the column types are different than you expect them to be based on a
CREATE TABLE statement, note that MySQL sometimes changes column
types. See section 6.5.3.1
Silent Column Specification Changes.
This statement is provided for Oracle compatibility.
The SHOW statement provides similar information. See section 4.5.6
SHOW Syntax.
BEGIN/COMMIT/ROLLBACK SyntaxBy default, MySQL runs in autocommit mode. This means that as
soon as you execute an update, MySQL will store the update on disk.
If you are using transactions safe tables (like InnoDB,
BDB, you can put MySQL into non-autocommit mode with
the following command:
SET AUTOCOMMIT=0
After this you must use COMMIT to store your changes to disk or
ROLLBACK if you want to ignore the changes you have made since the
beginning of your transaction.
If you want to switch from AUTOCOMMIT mode for one series of
statements, you can use the BEGIN or BEGIN WORK
statement:
BEGIN; SELECT @A:=SUM(salary) FROM table1 WHERE type=1; UPDATE table2 SET summmary=@A WHERE type=1; COMMIT;
Note that if you are using non-transaction-safe tables, the changes will be
stored at once, independent of the status of the autocommit mode.
If you do a ROLLBACK when you have updated a non-transactional
table you will get an error (ER_WARNING_NOT_COMPLETE_ROLLBACK) as a
warning. All transactional safe tables will be restored but any
non-transactional table will not change.
If you are using BEGIN or SET AUTOCOMMIT=0, you
should use the MySQL binary log for backups instead of the older update log.
Transactions are stored in the binary log in one chunk, upon
COMMIT, to ensure that transactions which are rolled back are not
stored. See section 4.9.4
The Binary Update Log.
The following commands automatically end a transaction (as if you had done a
COMMIT before executing the command):
| Command | Command | Command |
ALTER TABLE |
BEGIN |
CREATE INDEX |
DROP DATABASE |
DROP TABLE |
RENAME TABLE |
TRUNCATE |
You can change the isolation level for transactions with SET
TRANSACTION ISOLATION LEVEL .... See section 6.7.3
SET TRANSACTION Syntax.
LOCK TABLES/UNLOCK TABLES SyntaxLOCK TABLES tbl_name [AS alias] {READ | [READ LOCAL] | [LOW_PRIORITY] WRITE}
[, tbl_name {READ | [LOW_PRIORITY] WRITE} ...]
...
UNLOCK TABLES
LOCK TABLES locks tables for the current thread. UNLOCK
TABLES releases any locks held by the current thread. All tables that are
locked by the current thread are automatically unlocked when the thread issues
another LOCK TABLES, or when the connection to the server is
closed.
The main reasons to use LOCK TABLES are for emulating
transactions or getting more speed when updating tables. This is explained in
more detail later.
If a thread obtains a READ lock on a table, that thread (and all
other threads) can only read from the table. If a thread obtains a
WRITE lock on a table, then only the thread holding the lock can
READ from or WRITE to the table. Other threads are
blocked.
The difference between READ LOCAL and READ is that
READ LOCAL allows non-conflicting INSERT statements to
execute while the lock is held. This can't however be used if you are going to
manipulate the database files outside MySQL while you hold the lock.
When you use LOCK TABLES, you must lock all tables that you are
going to use and you must use the same alias that you are going to use in your
queries! If you are using a table multiple times in a query (with aliases), you
must get a lock for each alias!
WRITE locks normally have higher priority than READ
locks, to ensure that updates are processed as soon as possible. This means that
if one thread obtains a READ lock and then another thread requests
a WRITE lock, subsequent READ lock requests will wait
until the WRITE thread has gotten the lock and released it. You can
use LOW_PRIORITY WRITE locks to allow other threads to obtain
READ locks while the thread is waiting for the WRITE
lock. You should only use LOW_PRIORITY WRITE locks if you are sure
that there will eventually be a time when no threads will have a
READ lock.
LOCK TABLES works as follows:
This policy ensures that table locking is deadlock free. There is however other things one needs to be aware of with this schema:
If you are using a LOW_PRIORITY_WRITE lock for a table, this
means only that MySQL will wait for this particlar lock until there is no
threads that wants a READ lock. When the thread has got the
WRITE lock and is waiting to get the lock for the next table in the
lock table list, all other threads will wait for the WRITE lock to
be released. If this becomes a serious problem with your application, you should
consider converting some of your tables to transactions safe tables.
You can safely kill a thread that is waiting for a table lock with
KILL. See section 4.5.5
KILL Syntax.
Note that you should not lock any tables that you are using
with INSERT DELAYED. This is because that in this case the
INSERT is done by a separate thread.
Normally, you don't have to lock tables, as all single UPDATE
statements are atomic; no other thread can interfere with any other currently
executing SQL statement. There are a few cases when you would like to lock
tables anyway:
READ-locked table and no other
thread can read a WRITE-locked table. The reason some things are
faster under LOCK TABLES is that MySQL will not flush the key
cache for the locked tables until UNLOCK TABLES is called
(normally the key cache is flushed after each SQL statement). This speeds up
inserting/updateing/deletes on MyISAM tables.
LOCK TABLES if you want to ensure that
no other thread comes between a SELECT and an
UPDATE. The example shown below requires LOCK TABLES
in order to execute safely: mysql> LOCK TABLES trans READ, customer WRITE;
mysql> select sum(value) from trans where customer_id= some_id;
mysql> update customer set total_value=sum_from_previous_statement
where customer_id=some_id;
mysql> UNLOCK TABLES;
Without LOCK TABLES, there is a chance that another thread
might insert a new row in the trans table between execution of
the SELECT and UPDATE statements. By using incremental updates (UPDATE customer SET
value=value+new_value) or the LAST_INSERT_ID() function, you
can avoid using LOCK TABLES in many cases.
You can also solve some cases by using the user-level lock functions
GET_LOCK() and RELEASE_LOCK(). These locks are saved
in a hash table in the server and implemented with
pthread_mutex_lock() and pthread_mutex_unlock() for
high speed. See section 6.3.5.2
Miscellaneous Functions.
See section 5.3.1 How MySQL Locks Tables, for more information on locking policy.
You can lock all tables in all databases with read locks with the FLUSH
TABLES WITH READ LOCK command. See section 4.5.3
FLUSH Syntax. This is very convenient way to get backups if you
have a file system, like Veritas, that can take snapshots in time.
NOTE: LOCK TABLES is not transaction-safe and
will automatically commit any active transactions before attempting to lock the
tables.
SET TRANSACTION SyntaxSET [GLOBAL | SESSION] TRANSACTION ISOLATION LEVEL [READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE]
Sets the transaction isolation level for the global, whole session or the next transaction.
The default behavior is to set the isolation level for the next (not started) transaction.
If you set the GLOBAL privilege it will affect all new created
threads. You will need the PROCESS privilege to do do this.
Setting the SESSION privilege will affect the following and all
future transactions.
You can set the default isolation level for mysqld with
--transaction-isolation=.... See section 4.1.1
mysqld Command-line Options.
Since Version 3.23.23, MySQL has support for full-text indexing and
searching. Full-text indexes in MySQL are an index of type
FULLTEXT. FULLTEXT indexes can be created from
VARCHAR and TEXT columns at CREATE TABLE
time or added later with ALTER TABLE or CREATE INDEX.
For large datasets, adding FULLTEXT index with ALTER
TABLE (or CREATE INDEX) would be much faster than inserting
rows into the empty table that has a FULLTEXT index.
Full-text search is performed with the MATCH function.
mysql> CREATE TABLE articles (
-> id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
-> title VARCHAR(200),
-> body TEXT,
-> FULLTEXT (title,body)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO articles VALUES
-> (0,'MySQL Tutorial', 'DBMS stands for DataBase Management ...'),
-> (0,'How To Use MySQL Efficiently', 'After you went through a ...'),
-> (0,'Optimising MySQL','In this tutorial we will show how to ...'),
-> (0,'1001 MySQL Trick','1. Never run mysqld as root. 2. Normalise ...'),
-> (0,'MySQL vs. YourSQL', 'In the following database comparison we ...'),
-> (0,'MySQL Security', 'When configured properly, MySQL could be ...');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST ('database');
+----+-------------------+---------------------------------------------+
| id | title | body |
+----+-------------------+---------------------------------------------+
| 5 | MySQL vs. YourSQL | In the following database comparison we ... |
| 1 | MySQL Tutorial | DBMS stands for DataBase Management ... |
+----+-------------------+---------------------------------------------+
2 rows in set (0.00 sec)
The function MATCH matches a natural language (or boolean, see
below) query in case-insensitive fashion AGAINST a text collection
(which is simply the set of columns covered by a FULLTEXT index).
For every row in a table it returns relevance - a similarity measure between the
text in that row (in the columns that are part of the collection) and the query.
When it is used in a WHERE clause (see example above) the rows
returned are automatically sorted with relevance decreasing. Relevance is a
non-negative floating-point number. Zero relevance means no similarity.
Relevance is computed based on the number of words in the row, the number of
unique words in that row, the total number of words in the collection, and the
number of documents (rows) that contain a particular word.
The above is a basic example of using MATCH function. Rows are
returned with relevance decreasing.
mysql> SELECT id,MATCH title,body AGAINST ('Tutorial') FROM articles;
+----+-----------------------------------------+
| id | MATCH (title,body) AGAINST ('Tutorial') |
+----+-----------------------------------------+
| 1 | 0.64840710366884 |
| 2 | 0 |
| 3 | 0.66266459031789 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
+----+-----------------------------------------+
5 rows in set (0.00 sec)
This example shows how to retrieve the relevances. As neither
WHERE nor ORDER BY clauses are present, returned rows
are not ordered.
mysql> SELECT id, body, MATCH title,body AGAINST (
-> 'Security implications of running MySQL as root') AS score
-> FROM articles WHERE MATCH (title,body) AGAINST
-> ('Security implications of running MySQL as root');
+----+-----------------------------------------------+-----------------+
| id | body | score |
+----+-----------------------------------------------+-----------------+
| 4 | 1. Never run mysqld as root. 2. Normalise ... | 1.5055546709332 |
| 6 | When configured properly, MySQL could be ... | 1.31140957288 |
+----+-----------------------------------------------+-----------------+
2 rows in set (0.00 sec)
This is more complex example - the query returns the relevance and still
sorts the rows with relevance decreasing. To achieve it one should specify
MATCH twice. Note, that this will cause no additional overhead, as
MySQL optimiser will notice that these two MATCH calls are
identical and will call full-text search code only once.
MySQL uses a very simple parser to split text into words. A ``word'' is any sequence of letters, numbers, `'', and `_'. Any ``word'' that is present in the stopword list or just too short (3 characters or less) is ignored.
Every correct word in the collection and in the query is weighted, according to its significance in the query or collection. This way, a word that is present in many documents will have lower weight (and may even have a zero weight), because it has lower semantic value in this particular collection. Otherwise, if the word is rare, it will receive a higher weight. The weights of the words are then combined to compute the relevance of the row.
Such a technique works best with large collections (in fact, it was carefully tuned this way). For very small tables, word distribution does not reflect adequately their semantical value, and this model may sometimes produce bisarre results.
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST ('MySQL');
Empty set (0.00 sec)
Search for the word MySQL produces no results in the above
example. Word MySQL is present in more than half of rows, and as
such, is effectively treated as a stopword (that is, with semantical value
zero). It is, really, the desired behavior - a natural language query should not
return every second row in 1GB table.
A word that matches half of rows in a table is less likely to locate relevant documents. In fact, it will most likely find plenty of irrelevant documents. We all know this happens far too often when we are trying to find something on the Internet with a search engine. It is with this reasoning that such rows have been assigned a low semantical value in this particular dataset.
Since version 4.0.1 MySQL can also perform boolean fulltext searches using
IN BOOLEAN MODE modifier.
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST (
-> '+MySQL -YourSQL' IN BOOLEAN MODE);
+----+------------------------------+-----------------------------------------------+
| id | title | body |
+----+------------------------------+-----------------------------------------------+
| 1 | MySQL Tutorial | DBMS stands for DataBase Management ... |
| 2 | How To Use MySQL Efficiently | After you went through a ... |
| 3 | Optimising MySQL | In this tutorial we will show how to ... |
| 4 | 1001 MySQL Trick | 1. Never run mysqld as root. 2. Normalise ... |
| 6 | MySQL Security | When configured properly, MySQL could be ... |
+----+------------------------------+-----------------------------------------------+
This query retrieved all the rows that contain the word MySQL
(note: 50% threshold is gone), but does not contain the word
YourSQL. Note, that it does not auto-magically sort rows in
decreasing relevance order (the last row has the highest relevance, as it
contains MySQL twice). Boolean fulltext search can also work even
without FULLTEXT index, but it would be slow.
Boolean fulltext search supports the following operators:
+
-
MATCH ... AGAINST() without IN BOOLEAN MODE
modifier.
< >
( )
~
- operator.
*
And here are some examples:
apple banana
+apple +juice
+apple macintosh
+apple -macintosh
+apple +(>pie <strudel)
apple*
MATCH function must be columns from the
same table that is part of the same fulltext index, unless this
MATCH is IN BOOLEAN MODE.
MATCH and AGAINST must match
exactly a column list in the FULLTEXT index definition, unless
this MATCH is IN BOOLEAN MODE.
AGAINST must be a constant string. Unfortunately, full-text search has few user-tunable parameters yet, although adding some is very high on the TODO. If you have a MySQL source distribution (see section 2.3 Installing a MySQL Source Distribution), you can more control on the full-text search behavior.
Note that full-text search was carefully tuned for the best searching effectiveness. Modifying the default behavior will, in most cases, only make the search results worse. Do not alter the MySQL sources unless you know what you are doing!
ft_min_word_length. See section 4.5.6.4
SHOW VARIABLES. Change it to the value you prefer, and
rebuild your FULLTEXT indexes.
FULLTEXT indexes.
#define GWS_IN_USE GWS_PROBto
#define GWS_IN_USE GWS_FREQand recompile MySQL. There is no need to rebuild the indexes in this case. Note: by doing this you severely decrease MySQL ability to provide adequate relevance values by
MATCH function. It means, that if you really need to search for
such a common words, then you should rather search IN BOOLEAN
MODE, which does not has 50% threshold.
ft_boolean_syntax
variable. See section 4.5.6.4
SHOW VARIABLES. Still, this variable is read-only, its value
is set in `myisam/ft_static.c'. FULLTEXT index
faster.
FULLTEXT index (yes,
very slow).
MERGE tables.
FULLTEXT in CREATE/ALTER TABLE). From version 4.0.1, MySQL server features a Query
Cache. When in use, the query cache stores the text of a
SELECT query together with the corresponding result that is sent to
a client. If another identical query is received, the server can then retrieve
the results from the query cache rather than parsing and executing the same
query again.
The query cache is extremely useful in an environment where (some) tables don't change very often and you have a lot of identical queries. This is a typical situation for many web servers that use a lot of dynamic content.
Following are some performance data for the query cache (We got these by running the MySQL benchmark suite on a Linux Alpha 2x500 MHz with 2GB RAM and a 64MB query cache):
query_cache_size=0. By disabling the query cache code there is no
noticeable overhead.
Queries are compared before parsing, thus
SELECT * FROM TABLE
and
Select * from table
are regarded as different queries for query cache, so queries need to be exactly the same (byte for byte) to be seen as identical. In addition, a query may be seen as different if for instance one client is using a new communication protocol format or another character set than another client.
Queries that uses different databases, uses different protocol versions or the uses different default character sets are considered different queries and cached separately.
The cache does work for SELECT CALC_ROWS ... and SELECT
FOUND_ROWS() ... type queries because the number of found rows is also
stored in the cache.
If a table changes (INSERT, UPDATE,
DELETE, TRUNCATE, ALTER or DROP
TABLE|DATABASE), then all cached queries that used this table (possibly
through a MRG_MyISAM table!) become invalid and are removed from
the cache.
Currently all InnoDB tables are invalidated on
COMMIT, in the future this will be changed so only tables changed
in the transaction cause the corresponding cache entries to be invalidated.
A query cannot be cached if it contains one of the functions:
| Function | Function | Function | Function |
User Defined Functions |
CONNECTION_ID |
FOUND_ROWS |
GET_LOCK |
RELEASE_LOCK |
LOAD_FILE |
MASTER_POS_WAIT |
NOW |
SYSDATE |
CURRENT_TIMESTAMP |
CURDATE |
CURRENT_DATE |
CURTIME |
CURRENT_TIME |
DATABASE |
ENCRYPT (with one parameter) |
LAST_INSERT_ID |
RAND |
UNIX_TIMESTAMP (without parameters) |
USER |
BENCHMARK |
Nor can a query be cached if it contains user variables, if it is of the form
SELECT ... IN SHARE MODE or of the form SELECT * FROM
AUTOINCREMENT_FIELD IS NULL (to retrieve last insert id - ODBC work
around).
However, FOUND ROWS() will return the correct value, even if the
preceding query was fetched from the cache.
Queries that don't use any tables or if the user has a column privilege for any of the involved tables are not cached.
Before a query is fetched from the query cache, MySQL will check that the user has SELECT privilege to all the involved databases and tables. If this is not the case, the cached result will not be used.
The query cache adds a few MySQL system variables for
mysqld which may be set in a configuration file, on the command
line when starting mysqld.
query_cache_limit Don't cache results that are bigger than
this. (Default 1M).
query_cache_size The memory allocated to store results from
old queries. If this is 0, the query cache is disabled (default).
query_cache_startup_type This may be set (only numeric) to
| Option | Description |
| 0 | (OFF, don't cache or retrieve results) |
| 1 | (ON, cache all results except SELECT SQL_NO_CACHE ...
queries) |
| 2 | (DEMAND, cache only SELECT SQL_CACHE ... queries)
|
Inside a thread (connection), the behaviour of the query cache can be changed from the default. The syntax is as follows:
SQL_QUERY_CACHE_TYPE = OFF | ON | DEMAND
SQL_QUERY_CACHE_TYPE = 0 | 1 | 2
| Option | Description |
| 0 or OFF | Don't cache or retrieve results. |
| 1 or ON | Cache all results except SELECT SQL_NO_CACHE ... queries.
|
| 2 or DEMAND | Cache only SELECT SQL_CACHE ... queries.
|
By default SQL_QUERY_CACHE_TYPE depends on the value of
query_cache_startup_type when the thread was created.
SELECTThere are two possible query cache related parameters that may be specified
in a SELECT query:
| Option | Description |
SQL_CACHE |
If SQL_QUERY_CACHE_TYPE is DEMAND, allow the
query to be cached. If SQL_QUERY_CACHE_TYPE is
ON, this is the default. If SQL_QUERY_CACHE_TYPE
is OFF, do nothing. |
SQL_NO_CACHE |
Make this query non-cachable, don't allow this query to be stored in the cache. |
With the FLUSH QUERY CACHE command you can defragment the query
cache to better utilise its memory. This command will not remove any queries
from the cache. FLUSH TABLES also flushes the query cache.
The RESET QUERY CACHE command removes all query results from the
query cache.
You can monitor query cache performance in SHOW STATUS:
| Variable | Description |
Qcache_queries_in_cache |
Number of queries registered in the cache. |
Qcache_inserts |
Number of queries added to the cache. |
Qcache_hits |
Number of cache hits. |
Qcache_not_cached |
Number of non-cached queries (not cachable, or due to
SQL_QUERY_CACHE_TYPE). |
Qcache_free_memory |
Amount of free memory for query cache. |
Qcache_total_blocks |
Total number of blocks in query cache. |
Qcache_free_blocks |
Number of free memory blocks in query cache. |
Total number of queries = Qcache_inserts +
Qcache_hits + Qcache_not_cached.
The query cache uses variable length blocks, so
Qcache_total_blocks and Qcache_free_blocks may
indicate query cache memory fragmentation. After FLUSH QUERY CACHE
only a single (big) free block remains.
Note: Every query needs a minimum of two blocks (one for the query text and one or more for the query results). Also, every table that is used by a query needs one block, but if two or more queries use same table only one block needs to be allocated.
As of MySQL Version 3.23.6, you can choose between three basic table formats
(ISAM, HEAP and MyISAM. Newer MySQL may
support additional table type (InnoDB, or BDB),
depending on how you compile it. When you create a new table, you can tell MySQL
which table type it should use for the table. MySQL will always create a
.frm file to hold the table and column definitions. Depending on
the table type, the index and data will be stored in other files.
Note that to use InnoDB tables you have to use at least the
innodb_data_file_path startup option. See section 7.5.2
InnoDB Startup Options.
The default table type in MySQL is MyISAM. If you are trying to
use a table type that is not compiled-in or activated, MySQL will instead create
a table of type MyISAM. This is a very useful feature when you want
to copy tables between different SQL servers that supports different table types
(like copying tables to a slave that is optimised for speed by not having
transactional tables). This automatic table changing can however also be very
confusing for new MySQL users. We plan to fix this by introducing warnings in
MySQL 4.0 and giving a warning when a table type is automatically changed.
You can convert tables between different types with the ALTER
TABLE statement. See section 6.5.4
ALTER TABLE Syntax.
Note that MySQL supports two different kinds of tables: transaction-safe
tables (InnoDB and BDB) and not transaction-safe
tables (HEAP, ISAM, MERGE, and
MyISAM).
Advantages of transaction-safe tables (TST):
COMMIT command.
ROLLBACK to ignore your changes (if you are
not running in auto commit mode).
Advantages of not transaction-safe tables (NTST):
You can combine TST and NTST tables in the same statements to get the best of both worlds.
MyISAM is the default table type in MySQL Version 3.23. It's
based on the ISAM code and has a lot of useful extensions.
The index is stored in a file with the .MYI (MYIndex) extension,
and the data is stored in a file with the .MYD (MYData) extension.
You can check/repair MyISAM tables with the myisamchk
utility. See section 4.4.6.7
Using myisamchk for Crash Recovery. You can compress
MyISAM tables with myisampack to take up much less
space. See section 4.7.4
myisampack, The MySQL Compressed Read-only Table Generator.
The following is new in MyISAM:
MyISAM file that indicates whether or
not the table was closed correctly. If mysqld is started with
--myisam-recover, MyISAM tables will automatically
be checked and/or repaired on open if the table wasn't closed properly.
INSERT new rows in a table that doesn't have free
blocks in the middle of the data file, at the same time other threads are
reading from the table (concurrent insert). An free block can come from an
update of a dynamic length row with much data to a row with less data or when
deleting rows. When all free blocks are used up, all future inserts will be
concurrent again.
AUTO_INCREMENT column.
MyISAM will automatically update this on
INSERT/UPDATE. The AUTO_INCREMENT value can be reset
with myisamchk. This will make AUTO_INCREMENT
columns faster (at least 10 %) and old numbers will not be reused as with the
old ISAM. Note that when an AUTO_INCREMENT is
defined on the end of a multi-part-key the old behavior is still present.
AUTO_INCREMENT column) the key tree will be split so that the
high node only contains one key. This will improve the space utilisation in
the key tree.
BLOB and TEXT columns can be indexed.
NULL values are allowed in indexed columns. This takes 0-1
bytes/key.
myisamchk.
myisamchk will mark tables as checked if one runs it with
--update-state. myisamchk --fast will only check
those tables that don't have this mark.
myisamchk -a stores statistics for key parts (and not only
for whole keys as in ISAM).
myisampack can pack BLOB and
VARCHAR columns.
DATA/INDEX DIRECTORY="path" option to
CREATE TABLE). See section 6.5.3
CREATE TABLE Syntax. MyISAM also supports the following things, which MySQL will be
able to use in the near future:
VARCHAR type; A VARCHAR
column starts with a length stored in 2 bytes.
VARCHAR may have fixed or dynamic record length.
VARCHAR and CHAR may be up to 64K. All key
segments have their own language definition. This will enable MySQL to have
different language definitions per column.
UNIQUE. This will
allow you to have UNIQUE on any combination of columns in a
table. (You can't search on a UNIQUE computed index, however.)
Note that index files are usually much smaller with MyISAM than
with ISAM. This means that MyISAM will normally use
less system resources than ISAM, but will need more CPU when
inserting data into a compressed index.
The following options to mysqld can be used to change the
behavior of MyISAM tables. See section 4.5.6.4
SHOW VARIABLES.
| Option | Description |
--myisam-recover=# |
Automatic recover of crashed tables. |
-O myisam_sort_buffer_size=# |
Buffer used when recovering tables. |
--delay-key-write-for-all-tables |
Don't flush key buffers between writes for any MyISAM table |
-O myisam_max_extra_sort_file_size=# |
Used to help MySQL to decide when to use the slow but safe key cache index create method. Note that this parameter is given in megabytes! |
-O myisam_max_sort_file_size=# |
Don't use the fast sort index method to created index if the temporary file would get bigger than this. Note that this paramter is given in megabytes! |
-O myisam_bulk_insert_tree_size=# |
Size of tree cache used in bulk insert optimisation. Note that this is a limit per thread! |
The automatic recovery is activated if you start mysqld with
--myisam-recover=#. See section 4.1.1
mysqld Command-line Options. On open, the table is checked if it's marked as
crashed or if the open count variable for the table is not 0 and you are running
with --skip-locking. If either of the above is true the following
happens.
If the recover wouldn't be able to recover all rows from a previous completed
statement and you didn't specify FORCE as an option to
myisam-recover, then the automatic repair will abort with an error
message in the error file:
Error: Couldn't repair table: test.g00pages
If you in this case had used the FORCE option you would instead
have got a warning in the error file:
Warning: Found 344 of 354 rows when repairing ./test/g00pages
Note that if you run automatic recover with the BACKUP option,
you should have a cron script that automatically moves file with names like
`tablename-datetime.BAK' from the database directories to a backup
media.
See section 4.1.1 mysqld Command-line Options.
MySQL can support different index types, but the normal type is ISAM or
MyISAM. These use a B-tree index, and you can roughly calculate the size for the
index file as (key_length+4)/0.67, summed over all keys. (This is
for the worst case when all keys are inserted in sorted order and we don't have
any compressed keys.)
String indexes are space compressed. If the first index part is a string, it
will also be prefix compressed. Space compression makes the index file smaller
than the above figures if the string column has a lot of trailing space or is a
VARCHAR column that is not always used to the full length. Prefix
compression is used on keys that start with a string. Prefix compression helps
if there are many strings with an identical prefix.
In MyISAM tables, you can also prefix compress numbers by
specifying PACK_KEYS=1 when you create the table. This helps when
you have many integer keys that have an identical prefix when the numbers are
stored high-byte first.
MyISAM supports 3 different table types. Two of them are
chosen automatically depending on the type of columns you are using. The third,
compressed tables, can only be created with the myisampack tool.
When you CREATE or ALTER a table you can for tables
that doesn't have BLOB's force the table format to
DYNAMIC or FIXED with the ROW_FORMAT=#
table option. In the future you will be able to compress/decompress tables by
specifying ROW_FORMAT=compressed | default to ALTER
TABLE. See section 6.5.3
CREATE TABLE Syntax.
This is the default format. It's used when the table contains no
VARCHAR, BLOB, or TEXT columns.
This format is the simplest and most secure format. It is also the fastest of the on-disk formats. The speed comes from the easy way data can be found on disk. When looking up something with an index and static format it is very simple. Just multiply the row number by the row length.
Also, when scanning a table it is very easy to read a constant number of records with each disk read.
The security is evidenced if your computer crashes when writing to a
fixed-size MyISAM file, in which case myisamchk can easily figure
out where each row starts and ends. So it can usually reclaim all records except
the partially written one. Note that in MySQL all indexes can always be
reconstructed:
CHAR, NUMERIC, and DECIMAL
columns are space-padded to the column width.
myisamchk) unless a huge
number of records are deleted and you want to return free disk space to the
operating system.
This format is used if the table contains any VARCHAR,
BLOB, or TEXT columns or if the table was created with
ROW_FORMAT=dynamic.
This format is a little more complex because each row has to have a header that says how long it is. One record can also end up at more than one location when it is made longer at an update.
You can use OPTIMIZE table or
myisamchk to defragment a table. If you have static data that you
access/change a lot in the same table as some VARCHAR or
BLOB columns, it might be a good idea to move the dynamic columns
to other tables just to avoid fragmentation:
'') for string columns, or zero for numeric columns. (This isn't
the same as columns containing NULL values.) If a string column
has a length of zero after removal of trailing spaces, or a numeric column has
a value of zero, it is marked in the bit map and not saved to disk. Non-empty
strings are saved as a length byte plus the string contents.
myisamchk
-r from time to time to get better performance. Use myisamchk -ei
tbl_name for some statistics.
3 + (number of columns + 7) / 8 + (number of char columns) + packed size of numeric columns + length of strings + (number of NULL columns + 7) / 8There is a penalty of 6 bytes for each link. A dynamic record is linked whenever an update causes an enlargement of the record. Each new link will be at least 20 bytes, so the next enlargement will probably go in the same link. If not, there will be another link. You may check how many links there are with
myisamchk -ed. All links may be removed with myisamchk
-r. This is a read-only type that is generated with the optional
myisampack tool (pack_isam for ISAM
tables):
myisampack.
0 are stored using 1 bit.
BIGINT column
(8 bytes) may be stored as a TINYINT column (1 byte) if all
values are in the range 0 to 255.
ENUM.
BLOB or
TEXT columns.
myisamchk. The file format that MySQL uses to store data has been extensively tested, but there are always circumstances that may cause database tables to become corrupted.
Even if the MyISAM table format is very reliable (all changes to a table is written before the SQL statements returns) , you can still get corrupted tables if some of the following things happens:
mysqld process being killed in the middle of a write.
Typial typical symptoms for a corrupt table is:
Incorrect key file for table: '...'. Try to repair
it while selecting data from the table.
You can check if a table is ok with the command CHECK TABLE. See
section 4.4.4
CHECK TABLE Syntax.
You can repair a corrupted table with REPAIR TABLE. See section
4.4.5
REPAIR TABLE Syntax. You can also repair a table, when
mysqld is not running with the myisamchk command.
myisamchk syntax.
If your tables get corrupted a lot you should try to find the reason for this! See section A.4.1 What To Do If MySQL Keeps Crashing.
In this case the most important thing to know is if the table got corrupted
if the mysqld died (one can easily verify this by checking if there
is a recent row restarted mysqld in the mysqld error file). If this
isn't the case, then you should try to make a test case of this. See section E.1.6
Making a test case when you experience table corruption.
Each MyISAM .MYI file has in the header a counter
that can be used to check if a table has been closed properly.
If you get the following warning from CHECK TABLE or
myisamchk:
# clients is using or hasn't closed the table properly
this means that this counter has come out of sync. This doesn't mean that the table is corrupted, but means that you should at least do a check on the table to verify that it's okay.
The counter works as follows:
FLUSH or because there isn't room in the table cache) the counter
is decremented if the table has been updated at any point.
In other words, the only ways this can go out of sync are:
MyISAM tables are copied without a LOCK and
FLUSH TABLES.
myisamchk --repair or myisamchk
--update-stateon a table that was in use by mysqld.
mysqld servers are using the table and one has done a
REPAIR or CHECK of the table while it was in use by
another server. In this setup the CHECK is safe to do (even if
you will get the warning from other servers), but REPAIR should
be avoided as it currently replaces the data file with a new one, which is not
signaled to the other servers. MERGE tables are new in MySQL Version 3.23.25. The code is still
in gamma, but should be resonable stable.
A MERGE table (also known as a MRG_MyISAM table) is
a collection of identical MyISAM tables that can be used as one.
You can only SELECT, DELETE, and UPDATE
from the collection of tables. If you DROP the MERGE
table, you are only dropping the MERGE specification.
Note that DELETE FROM merge_table used without a
WHERE will only clear the mapping for the table, not delete
everything in the mapped tables. (We plan to fix this in 4.1).
With identical tables we mean that all tables are created with identical
column and key information. You can't put a MERGE over tables where the columns
are packed differently, doesn't have exactly the same columns or have the keys
in different order. Some of the tables can however be compressed with
myisampack. See section 4.7.4
myisampack, The MySQL Compressed Read-only Table Generator.
When you create a MERGE table, you will get a .frm
table definition file and a .MRG table list file. The
.MRG just contains a list of the index files (.MYI
files) that should be used as one. All used tables must be in the same database
as the MERGE table itself.
For the moment you need to have SELECT, UPDATE, and
DELETE privileges on the tables you map to a MERGE
table.
MERGE tables can help you solve the following problems:
myisampack, and then create a MERGE to use these as
one.
MERGE table on this could be much faster than using the big
table. (You can, of course, also use a RAID to get the same kind of benefits.)
MERGE tables active, with possible overlapping files.
MERGE file than trying to repair a real big file.
MERGE table uses the
index of the individual tables. It doesn't need to maintain an index of its
one. This makes MERGE table collections VERY fast to make or
remap. Note that you must specify the key definitions when you create a
MERGE table!.
MERGE table on them on demand.
This is much faster and will save a lot of disk space.
The disadvantages with MERGE tables are:
MyISAM tables for a
MERGE table.
AUTO_INCREMENT columns are not automatically updated on
INSERT.
REPLACE doesn't work.
MERGE tables uses more file descriptors. If you are using a
MERGE that maps over 10 tables and 10 users are using this,
you are using 10*10 + 10 file descriptors. (10 data files for 10 users and 10
shared index files.)
MERGE
handler will need to issue a read on all underlying tables to check which one
most closely matches the given key. If you then do a 'read-next' then the
merge table handler will need to search the read buffers to find the next key.
Only when one key buffer is used up, the handler will need to read the next
key block. This makes MERGE keys much slower on
eq_ref searches, but not much slower on ref
searches. See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
DROP TABLE, ALTER TABLE or
DELETE FROM table_name without a WHERE clause on any
of the table that is mapped by a MERGE table that is 'open'. If
you do this, the MERGE table may still refer to the original
table and you will get unexpected results. When you create a MERGE table you have to specify with
UNION(list-of-tables) which tables you want to use as one.
Optionally you can specify with INSERT_METHOD if you want insert
for the MERGE table to happen in the first or last table in the
UNION list. If you don't specify INSERT_METHOD or
specify NO, then all INSERT commands on the
MERGE table will return an error.
The following example shows you how to use MERGE tables:
CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY, message CHAR(20));
CREATE TABLE t2 (a INT AUTO_INCREMENT PRIMARY KEY, message CHAR(20));
INSERT INTO t1 (message) VALUES ("Testing"),("table"),("t1");
INSERT INTO t2 (message) VALUES ("Testing"),("table"),("t2");
CREATE TABLE total (a INT NOT NULL, message CHAR(20), KEY(a)) TYPE=MERGE UNION=(t1,t2) INSERT_METHOD=LAST;
Note that we didn't create a UNIQUE or PRIMARY KEY
in the total table as the key isn't going to be unique in the
total table.
Note that you can also manipulate the .MRG file directly from
the outside of the MySQL server:
shell> cd /mysql-data-directory/current-database shell> ls -1 t1.MYI t2.MYI > total.MRG shell> mysqladmin flush-tables
Now you can do things like:
mysql> select * from total; +---+---------+ | a | message | +---+---------+ | 1 | Testing | | 2 | table | | 3 | t1 | | 1 | Testing | | 2 | table | | 3 | t2 | +---+---------+
To remap a MERGE table you can do one of the following:
DROP the table and re-create it
ALTER TABLE table_name UNION(...)
.MRG file and issue a FLUSH TABLE on
the MERGE table and all underlying tables to force the handler to
read the new definition file. The following are the known problems with MERGE tables:
DELETE FROM merge_table used without a WHERE
will only clear the mapping for the table, not delete everything in the mapped
tables.
RENAME TABLE on a table used in an active MERGE
table may corrupt the table. This will be fixed in MySQL 4.0.x.
MERGE doesn't check if the
underlying tables are of compatible types. If you use MERGE
tables in this fashion, you are very likely to run into strange problems.
ALTER TABLE to first add an UNIQUE
index to a table used in a MERGE table and then use ALTER
TABLE to add a normal index on the MERGE table, the key
order will be different for the tables if there was an old non-unique key in
the table. This is because ALTER TABLE puts UNIQUE
keys before normal keys to be able to detect duplicate keys as early as
possible.
MERGE table efficiently and
may sometimes produce non-optimal joins. This will be fixed in MySQL 4.0.x.
DROP TABLE on a table that is in use by a MERGE
table will not work on Windows because the MERGE handler does the
table mapping hidden from the upper layer of MySQL. Because Windows doesn't
allow you to drop files that are open, you first must flush all
MERGE tables (with FLUSH TABLES) or drop the
MERGE table before dropping the table. We will fix this at the
same time we introduce VIEWs. You can also use the deprecated ISAM table type. This will
disappear rather soon (probably in MySQL 4.1) because MyISAM is a
better implementation of the same thing. ISAM uses a
B-tree index. The index is stored in a file with the
.ISM extension, and the data is stored in a file with the
.ISD extension. You can check/repair ISAM tables with
the isamchk utility. See section 4.4.6.7
Using myisamchk for Crash Recovery.
ISAM has the following features/properties:
Most of the things true for MyISAM tables are also true for
ISAM tables. See section 7.1 MyISAM
Tables. The major differences compared to MyISAM tables are:
ISAM tables are not binary portable across OS/Platforms.
pack_isam rather than with
myisampack. If you want to convert an ISAM table to a MyISAM
table so that you can use utilities such as mysqlcheck, use an
ALTER TABLE statement:
mysql> ALTER TABLE tbl_name TYPE = MYISAM;
The embedded MySQL versions doesn't support ISAM tables.
HEAP tables use a hashed index and are stored in memory. This
makes them very fast, but if MySQL crashes you will lose all data stored in
them. HEAP is very useful for temporary tables!
The MySQL internal HEAP tables use 100% dynamic hashing without
overflow areas. There is no extra space needed for free lists. HEAP
tables also don't have problems with delete + inserts, which normally is common
with hashed tables:
mysql> CREATE TABLE test TYPE=HEAP SELECT ip,SUM(downloads) as down
FROM log_table GROUP BY ip;
mysql> SELECT COUNT(ip),AVG(down) FROM test;
mysql> DROP TABLE test;
Here are some things you should consider when you use HEAP
tables:
MAX_ROWS in the
CREATE statement to ensure that you accidentally do not use all
memory.
= and <=>
(but are VERY fast).
HEAP tables can only use whole keys to search for a row;
compare this to MyISAM tables where any prefix of the key can be
used to find rows.
HEAP tables use a fixed record length format.
HEAP doesn't support BLOB/TEXT
columns.
HEAP doesn't support AUTO_INCREMENT columns.
HEAP doesn't support an index on a NULL column.
HEAP table (this isn't
common for hashed tables).
HEAP tables are shared between all clients (just like any
other table).
ORDER BY).
HEAP tables are allocated in small blocks. The
tables are 100% dynamic (on inserting). No overflow areas and no extra key
space are needed. Deleted rows are put in a linked list and are reused when
you insert new data into the table.
DELETE FROM heap_table,
TRUNCATE heap_table or DROP TABLE heap_table.
MyISAM table to a
HEAP table.
HEAP tables bigger than max_heap_table_size.
The memory needed for one row in a HEAP table is:
SUM_OVER_ALL_KEYS(max_length_of_key + sizeof(char*) * 2) + ALIGN(length_of_row+1, sizeof(char*))
sizeof(char*) is 4 on 32-bit machines and 8 on 64-bit machines.
InnoDB provides MySQL with a transaction-safe (ACID compliant)
table handler with commit, rollback, and crash recovery capabilities. InnoDB
does locking on row level and also provides an Oracle-style consistent
non-locking read in SELECTs. These features increase multiuser
concurrency and performance. There is no need for lock escalation in InnoDB,
because row level locks in InnoDB fit in very small space. InnoDB tables support
FOREIGN KEY constraints as the first table type in MySQL.
InnoDB has been designed for maximum performance when processing large data volumes. Its CPU efficiency is probably not matched by any other disk-based relational database engine.
Technically, InnoDB is a complete database backend placed under MySQL. InnoDB has its own buffer pool for caching data and indexes in main memory. InnoDB stores its tables and indexes in a tablespace, which may consist of several files. This is different from, for example, MyISAM tables where each table is stored as a separate file. InnoDB tables can be of any size also on those operating systems where file size is limited to 2 GB.
You can find the latest information about InnoDB at http://www.innodb.com/. The most up-to-date version of the InnoDB manual is always placed there, and you can also order commercial licenses and support for InnoDB.
InnoDB is currently (October 2001) used in production at several large database sites requiring high performance. The famous Internet news site Slashdot.org runs on InnoDB. Mytrix, Inc. stores over 1 TB of data in InnoDB, and another site handles an average load of 800 inserts/updates per second in InnoDB.
InnoDB tables are included in the MySQL source distribution starting from 3.23.34a and are activated in the MySQL -Max binary. For Windows the -Max binaries are contained in the standard distribution.
If you have downloaded a binary version of MySQL that includes support for InnoDB, simply follow the instructions of the MySQL manual for installing a binary version of MySQL. If you already have MySQL-3.23 installed, then the simplest way to install MySQL -Max is to replace the server executable `mysqld' with the corresponding executable in the -Max distribution. MySQL and MySQL -Max differ only in the server executable. See section 2.2.7 Installing a MySQL Binary Distribution. See section 4.7.5 mysqld-max, An extended mysqld server.
To compile MySQL with InnoDB support, download MySQL-3.23.34a or newer
version from http://mysql.com/ and configure
MySQL with the --with-innodb option. See the MySQL manual about
installing a MySQL source distribution. See section 2.3
Installing a MySQL Source Distribution.
cd /path/to/source/of/mysql-3.23.37 ./configure --with-innodb
To use InnoDB you have to specify InnoDB startup options in your
`my.cnf' or `my.ini' file. The minimal way to modify it is to
add to the [mysqld] section the line
innodb_data_file_path=ibdata:30M
but to get good performance it is best that you specify options like recommended below in the section 'InnoDB startup options'.
InnoDB is distributed under the GNU GPL License Version 2 (of June 1991). In the source distribution of MySQL, InnoDB appears as a subdirectory.
To use InnoDB tables you MUST specify configuration
parameters in the MySQL configuration file in the [mysqld] section
of the configuration file `my.cnf'. See section 4.1.2
my.cnf Option Files.
The only required parameter to use InnoDB is
innodb_data_file_path, but you should set others if you want to get
a better performance.
Suppose you have a Windows NT machine with 128 MB RAM and a single 10 GB hard disk. Below is an example of possible configuration parameters in `my.cnf' for InnoDB:
[mysqld] # You can write your other MySQL server options here # ... # innodb_data_file_path = ibdata1:2000M;ibdata2:2000M innodb_data_home_dir = c:\ibdata set-variable = innodb_mirrored_log_groups=1 innodb_log_group_home_dir = c:\iblogs set-variable = innodb_log_files_in_group=3 set-variable = innodb_log_file_size=30M set-variable = innodb_log_buffer_size=8M innodb_flush_log_at_trx_commit=1 #.._arch_dir must be the same as .._log_group_home_dir innodb_log_arch_dir = c:\iblogs innodb_log_archive=0 set-variable = innodb_buffer_pool_size=70M set-variable = innodb_additional_mem_pool_size=10M set-variable = innodb_file_io_threads=4 set-variable = innodb_lock_wait_timeout=50
Note that some operating systems restrict file size to < 2G. The total size of data files has to be >= 10 MB. InnoDB does not create directories: you have to create them yourself. Check that the MySQL server has the rights to create files in the directories you specify.
When you the first time create an InnoDB database, it is best that you start the MySQL server from the command prompt. Then InnoDB will print the information about the database creation to the screen, and you see what is happening. See below in section 3 what the printout should look like. For example, in Windows you can start `mysqld-max.exe' with:
your-path-to-mysqld>mysqld-max --standalone --console
Suppose you have a Linux machine with 512 MB RAM and three 20 GB hard disks (at directory paths `/', `/dr2' and `/dr3'). Below is an example of possible configuration parameters in `my.cnf' for InnoDB:
[mysqld] # You can write your other MySQL server options here # ... # innodb_data_file_path = ibdata/ibdata1:2000M;dr2/ibdata/ibdata2:2000M innodb_data_home_dir = / set-variable = innodb_mirrored_log_groups=1 innodb_log_group_home_dir = /dr3 set-variable = innodb_log_files_in_group=3 set-variable = innodb_log_file_size=50M set-variable = innodb_log_buffer_size=8M innodb_flush_log_at_trx_commit=1 #.._arch_dir must be the same as .._log_group_home_dir innodb_log_arch_dir = /dr3/iblogs innodb_log_archive=0 set-variable = innodb_buffer_pool_size=350M set-variable = innodb_additional_mem_pool_size=20M set-variable = innodb_file_io_threads=4 set-variable = innodb_lock_wait_timeout=50
Note that we have placed the two data files on different disks. The reason
for the name innodb_data_file_path is that you can also specify
paths to your data files, and innodb_data_home_dir is just
textually catenated before your data file paths, adding a possible slash or
backslash in between. InnoDB will fill the tablespace formed by the data files
from bottom up. In some cases it will improve the performance of the database if
all data is not placed on the same physical disk. Putting log files on a
different disk from data is very often beneficial for performance.
The meanings of the configuration parameters are the following:
| Option | Description |
innodb_data_home_dir |
The common part of the directory path for all InnoDB data files. |
innodb_data_file_path |
Paths to individual data files and their sizes. The full directory path to each data file is acquired by concatenating innodb_data_home_dir to the paths specified here. The file sizes are specified in megabytes, hence the 'M' after the size specification above. InnoDB also understands the abbreviation 'G', 1G meaning 1024M. Starting from 3.23.44 you can set the file size bigger than 4 GB on those operating systems which support big files. On some operating systems files must be < 2 GB. The sum of the sizes of the files must be at least 10 MB. |
innodb_mirrored_log_groups |
Number of identical copies of log groups we keep for the database. Currently this should be set to 1. |
innodb_log_group_home_dir |
Directory path to InnoDB log files. |
innodb_log_files_in_group |
Number of log files in the log group. InnoDB writes to the files in a circular fashion. Value 3 is recommended here. |
innodb_log_file_size |
Size of each log file in a log group in megabytes. Sensible values range from 1M to the size of the buffer pool specified below. The bigger the value, the less checkpoint flush activity is needed in the buffer pool, saving disk i/o. But bigger log files also mean that recovery will be slower in case of a crash. The combined size of log files must be < 4 GB on 32-bit computers. |
innodb_log_buffer_size |
The size of the buffer which InnoDB uses to write log to the log files on disk. Sensible values range from 1M to half the combined size of log files. A big log buffer allows large transactions to run without a need to write the log to disk until the transaction commit. Thus, if you have big transactions, making the log buffer big will save disk i/o. |
innodb_flush_log_at_trx_commit |
Normally this is set to 1, meaning that at a transaction commit the log is flushed to disk, and the modifications made by the transaction become permanent, and survive a database crash. If you are willing to compromise this safety, and you are running small transactions, you may set this to 0 to reduce disk i/o to the logs. |
innodb_log_arch_dir |
The directory where fully written log files would be archived if we
used log archiving. The value of this parameter should currently be set
the same as innodb_log_group_home_dir. |
innodb_log_archive |
This value should currently be set to 0. As recovery from a backup is done by MySQL using its own log files, there is currently no need to archive InnoDB log files. |
innodb_buffer_pool_size |
The size of the memory buffer InnoDB uses to cache data and indexes of its tables. The bigger you set this the less disk i/o is needed to access data in tables. On a dedicated database server you may set this parameter up to 80 % of the machine physical memory size. Do not set it too large, though, because competition of the physical memory may cause paging in the operating system. |
innodb_additional_mem_pool_size |
Size of a memory pool InnoDB uses to store data dictionary information and other internal data structures. A sensible value for this might be 2M, but the more tables you have in your application the more you will need to allocate here. If InnoDB runs out of memory in this pool, it will start to allocate memory from the operating system, and write warning messages to the MySQL error log. |
innodb_file_io_threads |
Number of file i/o threads in InnoDB. Normally, this should be 4, but on Windows disk i/o may benefit from a larger number. |
innodb_lock_wait_timeout |
Timeout in seconds an InnoDB transaction may wait for a lock before
being rolled back. InnoDB automatically detects transaction deadlocks in
its own lock table and rolls back the transaction. If you use LOCK
TABLES command, or other transaction-safe table handlers than
InnoDB in the same transaction, then a deadlock may arise which InnoDB
cannot notice. In cases like this the timeout is useful to resolve the
situation. |
innodb_flush_method |
(Available from 3.23.40 up.) The default value for this is
fdatasync. Another option is O_DSYNC.
|
Suppose you have installed MySQL and have edited `my.cnf' so that it contains the necessary InnoDB configuration parameters. Before starting MySQL you should check that the directories you have specified for InnoDB data files and log files exist and that you have access rights to those directories. InnoDB cannot create directories, only files. Check also you have enough disk space for the data and log files.
When you now start MySQL, InnoDB will start creating your data files and log files. InnoDB will print something like the following:
~/mysqlm/sql > mysqld InnoDB: The first specified data file /home/heikki/data/ibdata1 did not exist: InnoDB: a new database to be created! InnoDB: Setting file /home/heikki/data/ibdata1 size to 134217728 InnoDB: Database physically writes the file full: wait... InnoDB: Data file /home/heikki/data/ibdata2 did not exist: new to be created InnoDB: Setting file /home/heikki/data/ibdata2 size to 262144000 InnoDB: Database physically writes the file full: wait... InnoDB: Log file /home/heikki/data/logs/ib_logfile0 did not exist: new to be c reated InnoDB: Setting log file /home/heikki/data/logs/ib_logfile0 size to 5242880 InnoDB: Log file /home/heikki/data/logs/ib_logfile1 did not exist: new to be c reated InnoDB: Setting log file /home/heikki/data/logs/ib_logfile1 size to 5242880 InnoDB: Log file /home/heikki/data/logs/ib_logfile2 did not exist: new to be c reated InnoDB: Setting log file /home/heikki/data/logs/ib_logfile2 size to 5242880 InnoDB: Started mysqld: ready for connections
A new InnoDB database has now been created. You can connect to the MySQL
server with the usual MySQL client programs like mysql. When you
shut down the MySQL server with `mysqladmin shutdown', InnoDB output
will be like the following:
010321 18:33:34 mysqld: Normal shutdown 010321 18:33:34 mysqld: Shutdown Complete InnoDB: Starting shutdown... InnoDB: Shutdown completed
You can now look at the data files and logs directories and you will see the files created. The log directory will also contain a small file named `ib_arch_log_0000000000'. That file resulted from the database creation, after which InnoDB switched off log archiving. When MySQL is again started, the output will be like the following:
~/mysqlm/sql > mysqld InnoDB: Started mysqld: ready for connections
If something goes wrong in an InnoDB database creation, you should delete all files created by InnoDB. This means all data files, all log files, the small archived log file, and in the case you already did create some InnoDB tables, delete also the corresponding `.frm' files for these tables from the MySQL database directories. Then you can try the InnoDB database creation again.
Suppose you have started the MySQL client with the command mysql
test. To create a table in the InnoDB format you must specify TYPE
= InnoDB in the table creation SQL command:
CREATE TABLE CUSTOMER (A INT, B CHAR (20), INDEX (A)) TYPE = InnoDB;
This SQL command will create a table and an index on column A
into the InnoDB tablespace consisting of the data files you specified in
`my.cnf'. In addition MySQL will create a file `CUSTOMER.frm'
to the MySQL database directory `test'. Internally, InnoDB will add to
its own data dictionary an entry for table 'test/CUSTOMER'. Thus
you can create a table of the same name CUSTOMER in another
database of MySQL, and the table names will not collide inside InnoDB.
You can query the amount of free space in the InnoDB tablespace by issuing
the table status command of MySQL for any table you have created with TYPE
= InnoDB. Then the amount of free space in the tablespace appears in the
table comment section in the output of SHOW. An example:
SHOW TABLE STATUS FROM test LIKE 'CUSTOMER'
Note that the statistics SHOW gives about InnoDB tables are only
approximate: they are used in SQL optimisation. Table and index reserved sizes
in bytes are accurate, though.
InnoDB does not have a special optimisation for separate index creation.
Therefore it does not pay to export and import the table and create indexes
afterwards. The fastest way to alter a table to InnoDB is to do the inserts
directly to an InnoDB table, that is, use ALTER TABLE ...
TYPE=INNODB, or create an empty InnoDB table with identical definitions
and insert the rows with INSERT INTO ... SELECT * FROM ....
To get better control over the insertion process, it may be good to insert big tables in pieces:
INSERT INTO newtable SELECT * FROM oldtable WHERE yourkey > something
AND yourkey <= somethingelse;
After all data has been inserted you can rename the tables.
During the conversion of big tables you should set the InnoDB buffer pool size big to reduce disk i/o. Not bigger than 80 % of the physical memory, though. You should set InnoDB log files big, and also the log buffer large.
Make sure you do not run out of tablespace: InnoDB tables take a lot more
space than MyISAM tables. If an ALTER TABLE runs out of space, it
will start a rollback, and that can take hours if it is disk-bound. In inserts
InnoDB uses the insert buffer to merge secondary index records to indexes in
batches. That saves a lot of disk i/o. In rollback no such mechanism is used,
and the rollback can take 30 times longer than the insertion.
In the case of a runaway rollback, if you do not have valuable data in your database, it is better that you kill the database process and delete all InnoDB data and log files and all InnoDB table `.frm' files, and start your job again, rather than wait for millions of disk i/os to complete.
InnoDB version 3.23.44 features foreign key constraints. InnoDB is the first MySQL table type which allows you to define foreign key constraints to guard the integrity of your data.
The syntax of a foreign key constraint definition in InnoDB:
FOREIGN KEY (index_col_name, ...) REFERENCES table_name (index_col_name, ...)
An example:
CREATE TABLE parent(id INT NOT NULL, PRIMARY KEY (id)) TYPE=INNODB;
CREATE TABLE child(id INT, parent_id INT, INDEX par_ind (parent_id),
FOREIGN KEY (parent_id) REFERENCES parent(id)) TYPE=INNODB;
Both tables have to be InnoDB type and there must be an index where the
foreign key and the referenced key are listed as the first columns. Any
ALTER TABLE currently removes all foreign key constrainst defined
for the table, but not the constraints that reference the table. Corresponding
columns in the foreign key and the referenced key have to have similar internal
data types inside InnoDB so that they can be compared without a type conversion.
The length of string types need not be the same. The size and the signedness of
integer types has to be same.
When doing foreign key checks InnoDB sets shared row level locks on child or parent records it has to look at. InnoDB checks foreign key constraints immediately: the check is not deferred to transaction commit.
InnoDB allows you to drop any table even though that would break the foreign key constraints which reference the table. When you drop a table the constraints which were defined in its create statement are also dropped.
If you recreate a table which was dropped, it has to have a definition which conforms to the foreign key constraints referencing it. It must have the right column names and types, and it must have indexes on the referenced keys, as stated above.
You can list the foreign key constraints for a table T with
SHOW TABLE STATUS FROM yourdatabasename LIKE 'T';
The foreign key constraints are listed in the table comment of the output.
InnoDB does not yet support CASCADE ON DELETE or other special
options on the constraints.
You cannot increase the size of an InnoDB data file. To add more into your
tablespace you have to add a new data file. To do this you have to shut down
your MySQL database, edit the `my.cnf' file, adding a new file to
innodb_data_file_path, and then start MySQL again.
Currently you cannot remove a data file from InnoDB. To decrease the size of your database you have to use `mysqldump' to dump all your tables, create a new database, and import your tables to the new database.
If you want to change the number or the size of your InnoDB log files, you have to shut down MySQL and make sure that it shuts down without errors. Then copy the old log files into a safe place just in case something went wrong in the shutdown and you will need them to recover the database. Delete then the old log files from the log file directory, edit `my.cnf', and start MySQL again. InnoDB will tell you at the startup that it is creating new log files.
The key to safe database management is taking regular backups. To take a 'binary' backup of your database you have to do the following:
There is currently no on-line or incremental backup tool available for InnoDB, though they are in the TODO list.
In addition to taking the binary backups described above, you should also regularly take dumps of your tables with `mysqldump'. The reason to this is that a binary file may be corrupted without you noticing it. Dumped tables are stored into text files which are human-readable and much simpler than database binary files. Seeing table corruption from dumped files is easier, and since their format is simpler, the chance for serious data corruption in them is smaller.
A good idea is to take the dumps at the same time you take a binary backup of your database. You have to shut out all clients from your database to get a consistent snapshot of all your tables into your dumps. Then you can take the binary backup, and you will then have a consistent snapshot of your database in two formats.
To be able to recover your InnoDB database to the present from the binary backup described above, you have to run your MySQL database with the general logging and log archiving of MySQL switched on. Here by the general logging we mean the logging mechanism of the MySQL server which is independent of InnoDB logs.
To recover from a crash of your MySQL server process, the only thing you have to do is to restart it. InnoDB will automatically check the logs and perform a roll-forward of the database to the present. InnoDB will automatically roll back uncommitted transactions which were present at the time of the crash. During recovery, InnoDB will print out something like the following:
~/mysqlm/sql > mysqld InnoDB: Database was not shut down normally. InnoDB: Starting recovery from log files... InnoDB: Starting log scan based on checkpoint at InnoDB: log sequence number 0 13674004 InnoDB: Doing recovery: scanned up to log sequence number 0 13739520 InnoDB: Doing recovery: scanned up to log sequence number 0 13805056 InnoDB: Doing recovery: scanned up to log sequence number 0 13870592 InnoDB: Doing recovery: scanned up to log sequence number 0 13936128 ... InnoDB: Doing recovery: scanned up to log sequence number 0 20555264 InnoDB: Doing recovery: scanned up to log sequence number 0 20620800 InnoDB: Doing recovery: scanned up to log sequence number 0 20664692 InnoDB: 1 uncommitted transaction(s) which must be rolled back InnoDB: Starting rollback of uncommitted transactions InnoDB: Rolling back trx no 16745 InnoDB: Rolling back of trx no 16745 completed InnoDB: Rollback of uncommitted transactions completed InnoDB: Starting an apply batch of log records to the database... InnoDB: Apply batch completed InnoDB: Started mysqld: ready for connections
If your database gets corrupted or your disk fails, you have to do the recovery from a backup. In the case of corruption, you should first find a backup which is not corrupted. From a backup do the recovery from the general log files of MySQL according to instructions in the MySQL manual.
InnoDB implements a checkpoint mechanism called a fuzzy checkpoint. InnoDB will flush modified database pages from the buffer pool in small batches, there is no need to flush the buffer pool in one single batch, which would in practice stop processing of user SQL statements for a while.
In crash recovery InnoDB looks for a checkpoint label written to the log files. It knows that all modifications to the database before the label are already present on the disk image of the database. Then InnoDB scans the log files forward from the place of the checkpoint applying the logged modifications to the database.
InnoDB writes to the log files in a circular fashion. All committed modifications which make the database pages in the buffer pool different from the images on disk must be available in the log files in case InnoDB has to do a recovery. This means that when InnoDB starts to reuse a log file in the circular fashion, it has to make sure that the database page images on disk already contain the modifications logged in the log file InnoDB is going to reuse. In other words, InnoDB has to make a checkpoint and often this involves flushing of modified database pages to disk.
The above explains why making your log files very big may save disk i/o in checkpointing. It can make sense to set the total size of the log files as big as the buffer pool or even bigger. The drawback in big log files is that crash recovery can last longer because there will be more log to apply to the database.
InnoDB data and log files are binary-compatible on all platforms if the
floating point number format on the machines is the same. You can move an InnoDB
database simply by copying all the relevant files, which we already listed in
the previous section on backing up a database. If the floating point formats on
the machines are different but you have not used FLOAT or
DOUBLE data types in your tables then the procedure is the same:
just copy the relevant files. If the formats are different and your tables
contain floating point data, you have to use `mysqldump' and
`mysqlimport' to move those tables.
A performance tip is to switch off the auto commit when you import data into your database, assuming your tablespace has enough space for the big rollback segment the big import transaction will generate. Do the commit only after importing a whole table or a segment of a table.
In the InnoDB transaction model the goal has been to combine the best properties of a multiversioning database to traditional two-phase locking. InnoDB does locking on row level and runs queries by default as non-locking consistent reads, in the style of Oracle. The lock table in InnoDB is stored so space-efficiently that lock escalation is not needed: typically several users are allowed to lock every row in the database, or any random subset of the rows, without InnoDB running out of memory.
In InnoDB all user activity happens inside transactions. If the auto-commit
mode is used in MySQL, then each SQL statement will form a single transaction.
If the auto commit mode is switched off, then we can think that a user always
has a transaction open. If he issues the SQL COMMIT or
ROLLBACK statement, that ends the current transaction, and a new
starts. Both statements will release all InnoDB locks that were set during the
current transaction. A COMMIT means that the changes made in the
current transaction are made permanent and become visible to other users. A
ROLLBACK on the other hand cancels all modifications made by the
current transaction.
A consistent read means that InnoDB uses its multiversioning to present to a query a snapshot of the database at a point in time. The query will see the changes made by exactly those transactions that committed before that point of time, and no changes made by later or uncommitted transactions. The exception to this rule is that the query will see the changes made by the transaction itself which issues the query.
When a transaction issues its first consistent read, InnoDB assigns the snapshot, or the point of time, which all consistent reads in the same transaction will use. In the snapshot are all transactions that committed before assigning the snapshot. Thus the consistent reads within the same transaction will also be consistent with respect to each other. You can get a fresher snapshot for your queries by committing the current transaction and after that issuing new queries.
Consistent read is the default mode in which InnoDB processes
SELECT statements. A consistent read does not set any locks on the
tables it accesses, and therefore other users are free to modify those tables at
the same time a consistent read is being performed on the table.
A consistent read is not convenient in some circumstances. Suppose you want
to add a new row into your table CHILD, and make sure that the
child already has a parent in table PARENT.
Suppose you use a consistent read to read the table PARENT and
indeed see the parent of the child in the table. Can you now safely add the
child row to table CHILD? No, because it may happen that meanwhile
some other user has deleted the parent row from the table PARENT,
and you are not aware of that.
The solution is to perform the SELECT in a locking mode,
LOCK IN SHARE MODE.
SELECT * FROM PARENT WHERE NAME = 'Jones' LOCK IN SHARE MODE;
Performing a read in share mode means that we read the latest available data,
and set a shared mode lock on the rows we read. If the latest data belongs to a
yet uncommitted transaction of another user, we will wait until that transaction
commits. A shared mode lock prevents others from updating or deleting the row we
have read. After we see that the above query returns the parent
'Jones', we can safely add his child to table CHILD,
and commit our transaction. This example shows how to implement referential
integrity in your application code.
Let us look at another example: we have an integer counter field in a table
CHILD_CODES which we use to assign a unique identifier to each
child we add to table CHILD. Obviously, using a consistent read or
a shared mode read to read the present value of the counter is not a good idea,
since then two users of the database may see the same value for the counter, and
we will get a duplicate key error when we add the two children with the same
identifier to the table.
In this case there are two good ways to implement the reading and
incrementing of the counter: (1) update the counter first by incrementing it by
1 and only after that read it, or (2) read the counter first with a lock mode
FOR UPDATE, and increment after that:
SELECT COUNTER_FIELD FROM CHILD_CODES FOR UPDATE; UPDATE CHILD_CODES SET COUNTER_FIELD = COUNTER_FIELD + 1;
A SELECT ... FOR UPDATE will read the latest available data
setting exclusive locks on each row it reads. Thus it sets the same locks a
searched SQL UPDATE would set on the rows.
In row level locking InnoDB uses an algorithm called next-key locking. InnoDB does the row level locking so that when it searches or scans an index of a table, it sets shared or exclusive locks on the index records in encounters. Thus the row level locks are more precisely called index record locks.
The locks InnoDB sets on index records also affect the 'gap' before that
index record. If a user has a shared or exclusive lock on record R in an index,
then another user cannot insert a new index record immediately before R in the
index order. This locking of gaps is done to prevent the so-called phantom
problem. Suppose I want to read and lock all children with identifier bigger
than 100 from table CHILD, and update some field in the selected
rows.
SELECT * FROM CHILD WHERE ID > 100 FOR UPDATE;
Suppose there is an index on table CHILD on column
ID. Our query will scan that index starting from the first record
where ID is bigger than 100. Now, if the locks set on the index
records would not lock out inserts made in the gaps, a new child might meanwhile
be inserted to the table. If now I in my transaction execute
SELECT * FROM CHILD WHERE ID > 100 FOR UPDATE;
again, I will see a new child in the result set the query returns. This is against the isolation principle of transactions: a transaction should be able to run so that the data it has read does not change during the transaction. If we regard a set of rows as a data item, then the new 'phantom' child would break this isolation principle.
When InnoDB scans an index it can also lock the gap after the last record in
the index. Just that happens in the previous example: the locks set by InnoDB
will prevent any insert to the table where ID would be bigger than
100.
You can use next-key locking to implement a uniqueness check in your application: if you read your data in share mode and do not see a duplicate for a row you are going to insert, then you can safely insert your row and know that the next-key lock set on the successor of your row during the read will prevent anyone meanwhile inserting a duplicate for your row. Thus the next-key locking allows you to 'lock' the non-existence of something in your table.
SELECT ... FROM ... : this is a consistent read, reading a
snapshot of the database and setting no locks.
SELECT ... FROM ... LOCK IN SHARE MODE : sets shared next-key
locks on all index records the read encounters.
SELECT ... FROM ... FOR UPDATE : sets exclusive next-key
locks on all index records the read encounters.
INSERT INTO ... VALUES (...) : sets an exclusive lock on the
inserted row; note that this lock is not a next-key lock and does not prevent
other users from inserting to the gap before the inserted row. If a duplicate
key error occurs, sets a shared lock on the duplicate index record.
INSERT INTO T SELECT ... FROM S WHERE ... sets an exclusive
(non-next-key) lock on each row inserted into T. Does the search
on S as a consistent read, but sets shared next-key locks on
S if the MySQL logging is on. InnoDB has to set locks in the
latter case because in roll-forward recovery from a backup every SQL statement
has to be executed in exactly the same way as it was done originally.
CREATE TABLE ... SELECT ... performs the SELECT
as a consistent read or with shared locks, like in the previous item.
REPLACE is done like an insert if there is no collision on a
unique key. Otherwise, an exclusive next-key lock is placed on the row which
has to be updated.
UPDATE ... SET ... WHERE ... : sets an exclusive next-key
lock on every record the search encounters.
DELETE FROM ... WHERE ... : sets an exclusive next-key lock
on every record the search encounters.
FOREIGN KEY constraint is defined on a table, any
insert, update, or delete which requires checking of the constraint condition
sets shared record level locks on the records it looks at to check the
constraint. Also in the case where the constraint fails, InnoDB sets these
locks.
LOCK TABLES ... : sets table locks. In the implementation the
MySQL layer of code sets these locks. The automatic deadlock detection of
InnoDB cannot detect deadlocks where such table locks are involved: see the
next section below. See also section 13 'InnoDB restrictions' about the
following: since MySQL does know about row level locks, it is possible that
you get a table lock on a table where another user currently has row level
locks. But that does not put transaction integerity into danger. InnoDB automatically detects a deadlock of transactions and rolls back the
transaction whose lock request was the last one to build a deadlock, that is, a
cycle in the waits-for graph of transactions. InnoDB cannot detect deadlocks
where a lock set by a MySQL LOCK TABLES statement is involved, or
if a lock set in another table handler than InnoDB is involved. You have to
resolve these situations using innodb_lock_wait_timeout set in
`my.cnf'.
When InnoDB performs a complete rollback of a transaction, all the locks of the transaction are released. However, if just a single SQL statement is rolled back as a result of an error, some of the locks set by the SQL statement may be preserved. This is because InnoDB stores row locks in a format where it cannot afterwards know which was set by which SQL statement.
When you issue a consistent read, that is, an ordinary SELECT
statement, InnoDB will give your transaction a timepoint according to which your
query sees the database. Thus, if transaction B deletes a row and commits after
your timepoint was assigned, then you will not see the row deleted. Similarly
with inserts and updates.
You can advance your timepoint by committing your transaction and then doing
another SELECT.
This is called multiversioned concurrency control.
User A User B
set autocommit=0; set autocommit=0;
time
| SELECT * FROM t;
| empty set
| INSERT INTO t VALUES (1, 2);
|
v SELECT * FROM t;
empty set
COMMIT;
SELECT * FROM t;
empty set;
COMMIT;
SELECT * FROM t;
---------------------
| 1 | 2 |
---------------------
Thus user A sees the row inserted by B only when B has committed the insert, and A has committed his own transaction so that the timepoint is advanced past the the commit of B.
If you want to see the 'freshest' state of the database, you should use a locking read:
SELECT * FROM t LOCK IN SHARE MODE;
1. If the Unix `top' or the Windows `Task Manager' shows that the CPU usage percentage with your workload is less than 70 %, your workload is probably disk-bound. Maybe you are making too many transaction commits, or the buffer pool is too small. Making the buffer pool bigger can help, but do not set it bigger than 80 % of physical memory.
2. Wrap several modifications into one transaction. InnoDB must flush the log to disk at each transaction commit, if that transaction made modifications to the database. Since the rotation speed of a disk is typically at most 167 revolutions/second, that constrains the number of commits to the same 167/second if the disk does not fool the operating system.
3. If you can afford the loss of some latest committed
transactions, you can set the `my.cnf' parameter
innodb_flush_log_at_trx_commit to zero. InnoDB tries to flush the
log anyway once in a second, though the flush is not guaranteed.
4. Make your log files big, even as big as the buffer pool. When InnoDB has written the log files full, it has to write the modified contents of the buffer pool to disk in a checkpoint. Small log files will cause many unnecessary disk writes. The drawback in big log files is that recovery time will be longer.
5. Also the log buffer should be quite big, say 8 MB.
6. (Relevant from 3.23.39 up.) In some versions of Linux and
Unix, flushing files to disk with the Unix fdatasync and other
similar methods is surprisingly slow. The default method InnoDB uses is the
fdatasync function. If you are not satisfied with the database
write performance, you may try setting innodb_flush_method in
`my.cnf' to O_DSYNC, though O_DSYNC seems to be slower on
most systems.
7. In importing data to InnoDB, make sure that MySQL does
not have autocommit=1 on. Then every insert requires a log flush to
disk. Put before your plain SQL import file line
set autocommit=0;
and after it
commit;
If you use the `mysqldump' option --opt, you will get
dump files which are fast to import also to an InnoDB table, even without
wrapping them to the above set autocommit=0; ... commit; wrappers.
8. Beware of big rollbacks of mass inserts: InnoDB uses the insert buffer to save disk i/o in inserts, but in a corresponding rollback no such mechanism is used. A disk-bound rollback can take 30 times the time of the corresponding insert. Killing the database process will not help because the rollback will start again at the database startup. The only way to get rid of a runaway rollback is to increase the buffer pool so that the rollback becomes CPU-bound and runs fast, or delete the whole InnoDB database.
9. Beware also of other big disk-bound operations. Use
DROP TABLE or TRUNCATE (from MySQL-4.0 up) to empty a
table, not DELETE FROM yourtable.
10. Use the multi-line INSERT to reduce
communication overhead between the client and the server if you need to insert
many rows:
INSERT INTO yourtable VALUES (1, 2), (5, 5);
This tip is of course valid for inserts into any table type, not just InnoDB.
Starting from version 3.23.41 InnoDB includes the InnoDB Monitor which prints
information on the InnoDB internal state. When swithed on, InnoDB Monitor will
make the MySQL server `mysqld' to print data (note: the MySQL client
will not print anything) to the standard output about once every 15 seconds.
This data is useful in performance tuning. On Windows you must start
mysqld-max from a MS-DOS prompt with the --standalone
--console options to direct the output to the MS-DOS prompt window.
There is a separate innodb_lock_monitor which prints the same
information as innodb_monitor plus information on locks set by each
transaction.
The printed information includes data on:
You can start InnoDB Monitor through the following SQL command:
CREATE TABLE innodb_monitor(a int) type = innodb;
and stop it by
DROP TABLE innodb_monitor;
The CREATE TABLE syntax is just a way to pass a command to the
InnoDB engine through the MySQL SQL parser: the created table is not relevant at
all for InnoDB Monitor. If you shut down the database when the monitor is
running, and you want to start the monitor again, you have to drop the table
before you can issue a new CREATE TABLE to start the monitor. This
syntax may change in a future release.
A sample output of the InnoDB Monitor:
================================ 010809 18:45:06 INNODB MONITOR OUTPUT ================================ -------------------------- LOCKS HELD BY TRANSACTIONS -------------------------- LOCK INFO: Number of locks in the record hash table 1294 LOCKS FOR TRANSACTION ID 0 579342744 TABLE LOCK table test/mytable trx id 0 582333343 lock_mode IX RECORD LOCKS space id 0 page no 12758 n bits 104 table test/mytable index PRIMARY trx id 0 582333343 lock_mode X Record lock, heap no 2 PHYSICAL RECORD: n_fields 74; 1-byte offs FALSE; info bits 0 0: len 4; hex 0001a801; asc ;; 1: len 6; hex 000022b5b39f; asc ";; 2: len 7; hex 000002001e03ec; asc ;; 3: len 4; hex 00000001; ... ----------------------------------------------- CURRENT SEMAPHORES RESERVED AND SEMAPHORE WAITS ----------------------------------------------- SYNC INFO: Sorry, cannot give mutex list info in non-debug version! Sorry, cannot give rw-lock list info in non-debug version! ----------------------------------------------------- SYNC ARRAY INFO: reservation count 6041054, signal count 2913432 4a239430 waited for by thread 49627477 op. S-LOCK file NOT KNOWN line 0 Mut ex 0 sp 5530989 r 62038708 sys 2155035; rws 0 8257574 8025336; rwx 0 1121090 1848344 ----------------------------------------------------- CURRENT PENDING FILE I/O'S -------------------------- Pending normal aio reads: Reserved slot, messages 40157658 4a4a40b8 Reserved slot, messages 40157658 4a477e28 ... Reserved slot, messages 40157658 4a4424a8 Reserved slot, messages 40157658 4a39ea38 Total of 36 reserved aio slots Pending aio writes: Total of 0 reserved aio slots Pending insert buffer aio reads: Total of 0 reserved aio slots Pending log writes or reads: Reserved slot, messages 40158c98 40157f98 Total of 1 reserved aio slots Pending synchronous reads or writes: Total of 0 reserved aio slots ----------- BUFFER POOL ----------- LRU list length 8034 Free list length 0 Flush list length 999 Buffer pool size in pages 8192 Pending reads 39 Pending writes: LRU 0, flush list 0, single page 0 Pages read 31383918, created 51310, written 2985115 ---------------------------- END OF INNODB MONITOR OUTPUT ============================ 010809 18:45:22 InnoDB starts purge 010809 18:45:22 InnoDB purged 0 pages
Some notes on the output:
UNIV_SYNC_DEBUG defined in `univ.i'.
Since InnoDB is a multiversioned database, it must keep information of old versions of rows in the tablespace. This information is stored in a data structure we call a rollback segment after an analogous data structure in Oracle.
InnoDB internally adds two fields to each row stored in the database. A 6-byte field tells the transaction identifier for the last transaction which inserted or updated the row. Also a deletion is internally treated as an update where a special bit in the row is set to mark it as deleted. Each row also contains a 7-byte field called the roll pointer. The roll pointer points to an undo log record written to the rollback segment. If the row was updated, then the undo log record contains the information necessary to rebuild the content of the row before it was updated.
InnoDB uses the information in the rollback segment to perform the undo operations needed in a transaction rollback. It also uses the information to build earlier versions of a row for a consistent read.
Undo logs in the rollback segment are divided into insert and update undo logs. Insert undo logs are only needed in transaction rollback and can be discarded as soon as the transaction commits. Update undo logs are used also in consistent reads, and they can be discarded only after there is no transaction present for which InnoDB has assigned a snapshot that in a consistent read could need the information in the update undo log to build an earlier version of a database row.
You must remember to commit your transactions regularly, also those transactions which only issue consistent reads. Otherwise InnoDB cannot discard data from the update undo logs, and the rollback segment may grow too big, filling up your tablespace.
The physical size of an undo log record in the rollback segment is typically smaller than the corresponding inserted or updated row. You can use this information to calculate the space need for your rollback segment.
In our multiversioning scheme a row is not physically removed from the database immediately when you delete it with an SQL statement. Only when InnoDB can discard the update undo log record written for the deletion, it can also physically remove the corresponding row and its index records from the database. This removal operation is called a purge, and it is quite fast, usually taking the same order of time as the SQL statement which did the deletion.
MySQL stores its data dictionary information of tables in `.frm'
files in database directories. But every InnoDB type table also has its own
entry in InnoDB internal data dictionaries inside the tablespace. When MySQL
drops a table or a database, it has to delete both a `.frm' file or
files, and the corresponding entries inside the InnoDB data dictionary. This is
the reason why you cannot move InnoDB tables between databases simply by moving
the `.frm' files, and why DROP DATABASE did not work for
InnoDB type tables in MySQL versions <= 3.23.43.
Every InnoDB table has a special index called the clustered index where the
data of the rows is stored. If you define a PRIMARY KEY on your
table, then the index of the primary key will be the clustered index.
If you do not define a primary key for your table, InnoDB will internally generate a clustered index where the rows are ordered by the row id InnoDB assigns to the rows in such a table. The row id is a 6-byte field which monotonically increases as new rows are inserted. Thus the rows ordered by the row id will be physically in the insertion order.
Accessing a row through the clustered index is fast, because the row data will be on the same page where the index search leads us. In many databases the data is traditionally stored on a different page from the index record. If a table is large, the clustered index architecture often saves a disk i/o when compared to the traditional solution.
The records in non-clustered indexes (we also call them secondary indexes), in InnoDB contain the primary key value for the row. InnoDB uses this primary key value to search for the row from the clustered index. Note that if the primary key is long, the secondary indexes will use more space.
All indexes in InnoDB are B-trees where the index records are stored in the leaf pages of the tree. The default size of an index page is 16 kB. When new records are inserted, InnoDB tries to leave 1 / 16 of the page free for future insertions and updates of the index records.
If index records are inserted in a sequential (ascending or descending) order, the resulting index pages will be about 15/16 full. If records are inserted in a random order, then the pages will be 1/2 - 15/16 full. If the fillfactor of an index page drops below 1/2, InnoDB will try to contract the index tree to free the page.
It is a common situation in a database application that the primary key is a unique identifier and new rows are inserted in the ascending order of the primary key. Thus the insertions to the clustered index do not require random reads from a disk.
On the other hand, secondary indexes are usually non-unique and insertions happen in a relatively random order into secondary indexes. This would cause a lot of random disk i/o's without a special mechanism used in InnoDB.
If an index record should be inserted to a non-unique secondary index, InnoDB checks if the secondary index page is already in the buffer pool. If that is the case, InnoDB will do the insertion directly to the index page. But, if the index page is not found from the buffer pool, InnoDB inserts the record to a special insert buffer structure. The insert buffer is kept so small that it entirely fits in the buffer pool, and insertions can be made to it very fast.
The insert buffer is periodically merged to the secondary index trees in the database. Often we can merge several insertions on the same page in of the index tree, and hence save disk i/o's. It has been measured that the insert buffer can speed up insertions to a table up to 15 times.
If a database fits almost entirely in main memory, then the fastest way to perform queries on it is to use hash indexes. InnoDB has an automatic mechanism which monitors index searches made to the indexes defined for a table, and if InnoDB notices that queries could benefit from building of a hash index, such an index is automatically built.
But note that the hash index is always built based on an existing B-tree index on the table. InnoDB can build a hash index on a prefix of any length of the key defined for the B-tree, depending on what search pattern InnoDB observes on the B-tree index. A hash index can be partial: it is not required that the whole B-tree index is cached in the buffer pool. InnoDB will build hash indexes on demand to those pages of the index which are often accessed.
In a sense, through the adaptive hash index mechanism InnoDB adapts itself to ample main memory, coming closer to the architecture of main memory databases.
After a database startup, when a user first does an insert to a table
T where an auto-increment column has been defined, and the user
does not provide an explicit value for the column, then InnoDB executes
SELECT MAX(auto-inc-column) FROM T, and assigns that value
incremented by one to the the column and the auto-increment counter of the
table. We say that the auto-increment counter for table T has been
initialized.
InnoDB follows the same procedure in initializing the auto-increment counter for a freshly created table.
Note that if the user specifies in an insert the value 0 to the auto-increment column, then InnoDB treats the row like the value would not have been specified.
After the auto-increment counter has been initialized, if a user inserts a row where he explicitly specifies the column value, and the value is bigger than the current counter value, then the counter is set to the specified column value. If the user does not explicitly specify a value, then InnoDB increments the counter by one and assigns its new value to the column.
The auto-increment mechanism, when assigning values from the counter, bypasses locking and transaction handling. Therefore you may also get gaps in the number sequence if you roll back transactions which have got numbers from the counter.
The behavior of auto-increment is not defined if a user gives a negative value to the column or if the value becomes bigger than the maximum integer that can be stored in the specified integer type.
In disk i/o InnoDB uses asynchronous i/o. On Windows NT it uses the native asynchronous i/o provided by the operating system. On Unix, InnoDB uses simulated asynchronous i/o built into InnoDB: InnoDB creates a number of i/o threads to take care of i/o operations, such as read-ahead. In a future version we will add support for simulated aio on Windows NT and native aio on those versions of Unix which have one.
On Windows NT InnoDB uses non-buffered i/o. That means that the disk pages InnoDB reads or writes are not buffered in the operating system file cache. This saves some memory bandwidth.
Starting from 3.23.41 InnoDB uses a novel file flush technique called doublewrite. It adds safety to crash recovery after an operating system crash or a power outage, and improves performance on most Unix flavors by reducing the need for fsync operations.
Doublewrite means that InnoDB before writing pages to a data file first writes them to a contiguous tablespace area called the doublewrite buffer. Only after the write and the flush to the doublewrite buffer has completed, InnoDB writes the pages to their proper positions in the data file. If the operating system crashes in the middle of a page write, InnoDB will in recovery find a good copy of the page from the doublewrite buffer.
Starting from 3.23.41 you can also use a raw disk partition as a data file,
though this has not been tested yet. When you create a new data file you have to
put the keyword newraw immediately after the data file size in
innodb_data_file_path. The partition must be >= than you specify
as the size. Note that 1M in InnoDB is 1024 x 1024 bytes, while in disk
specifications 1 MB usually means 1000 000 bytes.
innodb_data_file_path=hdd1:5Gnewraw;hdd2:2Gnewraw
When you start the database again you must change the
keyword to raw. Otherwise InnoDB will write over your partition!
innodb_data_file_path=hdd1:5Graw;hdd2:2Graw
By using a raw disk you can on some Unixes perform unbuffered i/o.
There are two read-ahead heuristics in InnoDB: sequential read-ahead and random read-ahead. In sequential read-ahead InnoDB notices that the access pattern to a segment in the tablespace is sequential. Then InnoDB will post in advance a batch of reads of database pages to the i/o system. In random read-ahead InnoDB notices that some area in a tablespace seems to be in the process of being fully read into the buffer pool. Then InnoDB posts the remaining reads to the i/o system.
The data files you define in the configuration file form the tablespace of InnoDB. The files are simply catenated to form the tablespace, there is no striping in use. Currently you cannot directly instruct where the space is allocated for your tables, except by using the following fact: from a newly created tablespace InnoDB will allocate space starting from the low end.
The tablespace consists of database pages whose default size is 16 kB. The pages are grouped into extents of 64 consecutive pages. The 'files' inside a tablespace are called segments in InnoDB. The name of the rollback segment is somewhat misleading because it actually contains many segments in the tablespace.
For each index in InnoDB we allocate two segments: one is for non-leaf nodes of the B-tree, the other is for the leaf nodes. The idea here is to achieve better sequentiality for the leaf nodes, which contain the data.
When a segment grows inside the tablespace, InnoDB allocates the first 32 pages to it individually. After that InnoDB starts to allocate whole extents to the segment. InnoDB can add to a large segment up to 4 extents at a time to ensure good sequentiality of data.
Some pages in the tablespace contain bitmaps of other pages, and therefore a few extents in an InnoDB tablespace cannot be allocated to segments as a whole, but only as individual pages.
When you issue a query SHOW TABLE STATUS FROM ... LIKE ... to
ask for available free space in the tablespace, InnoDB will report you the space
which is certainly usable in totally free extents of the tablespace. InnoDB
always reserves some extents for clean-up and other internal purposes; these
reserved extents are not included in the free space.
When you delete data from a table, InnoDB will contract the corresponding B-tree indexes. It depends on the pattern of deletes if that frees individual pages or extents to the tablespace, so that the freed space is available for other users. Dropping a table or deleting all rows from it is guaranteed to release the space to other users, but remember that deleted rows can be physically removed only in a purge operation after they are no longer needed in transaction rollback or consistent read.
If there are random insertions or deletions in the indexes of a table, the indexes may become fragmented. By fragmentation we mean that the physical ordering of the index pages on the disk is not close to the alphabetical ordering of the records on the pages, or that there are many unused pages in the 64-page blocks which were allocated to the index.
It can speed up index scans if you periodically use mysqldump to
dump the table to a text file, drop the table, and reload it from the dump.
Another way to do the defragmenting is to ALTER the table type to
MyISAM and back to InnoDB again. Note that a
MyISAM table must fit in a single file on your operating system.
If the insertions to and index are always ascending and records are deleted only from the end, then the the file space management algorithm of InnoDB guarantees that fragmentation in the index will not occur.
The error handling in InnoDB is not always the same as specified in the ANSI SQL standards. According to the ANSI standard, any error during an SQL statement should cause the rollback of that statement. InnoDB sometimes rolls back only part of the statement, or the whole transaction. The following list specifies the error handling of InnoDB.
'Table is full' error and InnoDB rolls back the SQL statement.
INSERT INTO ... SELECT .... This will
probably change so that the SQL statement will be rolled back if you have not
specified the IGNORE option in your statement.
SHOW TABLE STATUS does not give accurate statistics on InnoDB
tables, except for the physical size reserved by the table. The row count is
only a rough estimate used in SQL optimisation.
CREATE TABLE T (A CHAR(20), B INT, UNIQUE (A(5))) TYPE = InnoDB;If you create a non-unique index on a prefix of a column, InnoDB will create an index over the whole column.
INSERT DELAYED is not supported for InnoDB tables.
LOCK TABLES operation does not know of InnoDB row
level locks set in already completed SQL statements: this means that you can
get a table lock on a table even if there still exist transactions of other
users which have row level locks on the same table. Thus your operations on
the table may have to wait if they collide with these locks of other users.
Also a deadlock is possible. However, this does not endanger transaction
integrity, because the row level locks set by InnoDB will always take care of
the integrity. Also, a table lock prevents other transactions from acquiring
more row level locks (in a conflicting lock mode) on the table.
BLOB or TEXT column.
DELETE FROM TABLE does not regenerate the table but instead
deletes all rows, one by one, which is not that fast. In future versions of
MySQL you can use TRUNCATE which is fast.
Contact information of Innobase Oy, producer of the InnoDB engine. Web site: http://www.innodb.com/. Email: Heikki.Tuuri@innodb.com
phone: 358-9-6969 3250 (office) 358-40-5617367 (mobile) Innobase Oy Inc. World Trade Center Helsinki Aleksanterinkatu 17 P.O.Box 800 00101 Helsinki Finland
Support for BDB tables is included in the MySQL source distribution starting from Version 3.23.34 and is activated in the MySQL-Max binary.
BerkeleyDB, available at http://www.sleepycat.com/ has provided
MySQL with a transactional table handler. By using BerkeleyDB tables, your
tables may have a greater chance of surviving crashes, and also provides
COMMIT and ROLLBACK on transactions. The MySQL source
distribution comes with a BDB distribution that has a couple of small patches to
make it work more smoothly with MySQL. You can't use a non-patched
BDB version with MySQL.
We at MySQL AB are working in close cooperation with Sleepycat to keep the quality of the MySQL/BDB interface high.
When it comes to supporting BDB tables, we are committed to help our users to locate the problem and help creating a reproducable test case for any problems involving BDB tables. Any such test case will be forwarded to Sleepycat who in turn will help us find and fix the problem. As this is a two stage operation, any problems with BDB tables may take a little longer for us to fix than for other table handlers. However, as the BerkeleyDB code itself has been used by many other applications than MySQL, we don't envision any big problems with this. See section 1.4.1 Support Offered by MySQL AB.
If you have downloaded a binary version of MySQL that includes support for BerkeleyDB, simply follow the instructions for installing a binary version of MySQL. See section 2.2.7 Installing a MySQL Binary Distribution. See section 4.7.5 mysqld-max, An extended mysqld server.
To compile MySQL with Berkeley DB support, download MySQL Version 3.23.34 or
newer and configure MySQL with the --with-berkeley-db
option. See section 2.3
Installing a MySQL Source Distribution.
cd /path/to/source/of/mysql-3.23.34 ./configure --with-berkeley-db
Please refer to the manual provided with the BDB distribution
for more updated information.
Even though Berkeley DB is in itself very tested and reliable, the MySQL interface is still considered beta quality. We are actively improving and optimising it to get it stable very soon.
If you are running with AUTOCOMMIT=0 then your changes in
BDB tables will not be updated until you execute
COMMIT. Instead of commit you can execute ROLLBACK to
forget your changes. See section 6.7.1
BEGIN/COMMIT/ROLLBACK Syntax.
If you are running with AUTOCOMMIT=1 (the default), your changes
will be committed immediately. You can start an extended transaction with the
BEGIN WORK SQL command, after which your changes will not be
committed until you execute COMMIT (or decide to
ROLLBACK the changes).
The following options to mysqld can be used to change the
behavior of BDB tables:
| Option | Description |
--bdb-home=directory |
Base directory for BDB tables. This should be the same directory you use for --datadir. |
--bdb-lock-detect=# |
Berkeley lock detect. One of (DEFAULT, OLDEST, RANDOM, or YOUNGEST). |
--bdb-logdir=directory |
Berkeley DB log file directory. |
--bdb-no-sync |
Don't synchronously flush logs. |
--bdb-no-recover |
Don't start Berkeley DB in recover mode. |
--bdb-shared-data |
Start Berkeley DB in multi-process mode (Don't use
DB_PRIVATE when initialising Berkeley DB) |
--bdb-tmpdir=directory |
Berkeley DB tempfile name. |
--skip-bdb |
Don't use berkeley db. |
-O bdb_max_lock=1000 |
Set the maximum number of locks possible. See section 4.5.6.4
SHOW VARIABLES. |
If you use --skip-bdb, MySQL will not initialise the Berkeley DB
library and this will save a lot of memory. Of course, you cannot use
BDB tables if you are using this option.
Normally you should start mysqld without
--bdb-no-recover if you intend to use BDB tables. This may,
however, give you problems when you try to start mysqld if the BDB
log files are corrupted. See section 2.4.2
Problems Starting the MySQL Server.
With bdb_max_lock you can specify the maximum number of locks
(10000 by default) you can have active on a BDB table. You should increase this
if you get errors of type bdb: Lock table is out of available locks
or Got error 12 from ... when you have do long transactions or when
mysqld has to examine a lot of rows to calculate the query.
You may also want to change binlog_cache_size and
max_binlog_cache_size if you are using big multi-line transactions.
See section 6.7.1
BEGIN/COMMIT/ROLLBACK Syntax.
BDB
tables:--bdb_log_dir options.
FLUSH LOGS at any time to checkpoint the Berkeley DB
tables. For disaster recovery, one should use table backups plus MySQL's
binary log. See section 4.4.1
Database Backups. Warning: If you delete old log files
that are in use, BDB will not be able to do recovery at all and you may lose
data if something goes wrong.
PRIMARY KEY in each BDB table to be able to
refer to previously read rows. If you don't create one, MySQL will create an
maintain a hidden PRIMARY KEY for you. The hidden key has a
length of 5 bytes and is incremented for each insert attempt.
BDB table are part of the same
index or part of the primary key, then MySQL can execute the query without
having to access the actual row. In a MyISAM table the above
holds only if the columns are part of the same index.
PRIMARY KEY will be faster than any other key, as the
PRIMARY KEY is stored together with the row data. As the other
keys are stored as the key data + the PRIMARY KEY, it's important
to keep the PRIMARY KEY as short as possible to save disk and get
better speed.
LOCK TABLES works on BDB tables as with other
tables. If you don't use LOCK TABLE, MySQL will issue an internal
multiple-write lock on the table to ensure that the table will be properly
locked if another thread issues a table lock.
BDB tables is done on page level.
SELECT COUNT(*) FROM table_name is slow as BDB
tables doesn't maintain a count of the number of rows in the table.
MyISAM tables as one has data in
BDB tables stored in B-trees and not in a separate data file.
BDB table may make an automatic rollback and any read may
fail with a deadlock error.
BDB tables compared to MyISAM tables which don't use
PACK_KEYS=0.
DELETE or ROLLBACK:s this number should be accurate
enough for the MySQL optimiser, but as MySQL only store the number on close,
it may be wrong if MySQL dies unexpectedly. It should not be fatal even if
this number is not 100 % correct. One can update the number of rows by
executing ANALYZE TABLE or OPTIMIZE TABLE. See
section 4.5.2
ANALYZE TABLE Syntax . See section 4.5.1
OPTIMIZE TABLE Syntax.
BDB table, you will get an error
(probably error 28) and the transaction should roll back. This is in contrast
with MyISAM and ISAM tables where
mysqld will wait for enough free disk before continuing. --no-auto-rehash with the mysql
client. We plan to partly fix this in 4.0.
SHOW TABLE STATUS doesn't yet provide that much information
for BDB tables.
If you after having built MySQL with support for BDB tables get the following
error in the log file when you start mysqld:
bdb: architecture lacks fast mutexes: applications cannot be threaded Can't init dtabases
This means that BDB tables are not supported for your
architecture. In this case you have to rebuild MySQL without BDB table support.
NOTE: The following list is not complete; We will update this as we get more information about this.
Currently we know that BDB tables works with the following operating system.
It doesn't work with the following operating systems:
hostname.err log when
starting mysqld: bdb: Ignoring log file: .../log.XXXXXXXXXX: unsupported log version #it means that the new
BDB version doesn't support the old
log file format. In this case you have to delete all BDB log BDB
from your database directory (the files that has the format
log.XXXXXXXXXX ) and restart mysqld. We would also
recommend you to do a mysqldump --opt of your old
BDB tables, delete the old table and restore the dump.
auto_commit mode and delete a table
you are using by another thread you may get the following error messages in
the MySQL error file: 001119 23:43:56 bdb: Missing log fileid entry 001119 23:43:56 bdb: txn_abort: Log undo failed for LSN: 1 3644744: InvalidThis is not fatal but we don't recommend that you delete tables if you are not in
auto_commit mode, until this problem is fixed (the fix
is not trivial). This chapter describes the APIs available for MySQL, where to get them, and how to use them. The C API is the most extensively covered, as it was developed by the MySQL team, and is the basis for most of the other APIs.
PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic Web pages. It contains support for accessing several databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache Web server.
The distribution and documentation are available at the PHP web site (http://www.php.net/).
-lz last when linking with
-lmysqlclient. This section documents the Perl DBI interface. The former
interface was called mysqlperl. DBI/DBD
now is the recommended Perl interface, so mysqlperl is obsolete and
is not documented here.
DBI with DBD::mysqlDBI is a generic interface for many databases. That means that
you can write a script that works with many different database engines without
change. You need a DataBase Driver (DBD) defined for each database type. For
MySQL, this driver is called DBD::mysql.
For more information on the Perl5 DBI, please visit the DBI Web
page and read the documentation:
http://www.symbolstone.org/technology/perl/DBI/
For more information on Object Oriented Programming (OOP) as defined in Perl5, see the Perl OOP page:
http://language.perl.com/info/documentation.html
Note that if you want to use transactions with Perl, you need to have
Msql-Mysql-modules version 1.2216 or newer.
Installation instructions for MySQL Perl support are given in section 2.7 Perl Installation Comments.
DBI InterfacePortable DBI Methods
| Method | Description |
connect |
Establishes a connection to a database server. |
disconnect |
Disconnects from the database server. |
prepare |
Prepares a SQL statement for execution. |
execute |
Executes prepared statements. |
do |
Prepares and executes a SQL statement. |
quote |
Quotes string or BLOB values to be inserted. |
fetchrow_array |
Fetches the next row as an array of fields. |
fetchrow_arrayref |
Fetches next row as a reference array of fields. |
fetchrow_hashref |
Fetches next row as a reference to a hashtable. |
fetchall_arrayref |
Fetches all data as an array of arrays. |
finish |
Finishes a statement and lets the system free resources. |
rows |
Returns the number of rows affected. |
data_sources |
Returns an array of databases available on localhost. |
ChopBlanks |
Controls whether fetchrow_* methods trim spaces. |
NUM_OF_PARAMS |
The number of placeholders in the prepared statement. |
NULLABLE |
Which columns can be NULL. |
trace |
Perform tracing for debugging. |
MySQL-specific Methods
| Method | Description |
insertid |
The latest AUTO_INCREMENT value. |
is_blob |
Which columns are BLOB values. |
is_key |
Which columns are keys. |
is_num |
Which columns are numeric. |
is_pri_key |
Which columns are primary keys. |
is_not_null |
Which columns CANNOT be NULL. See NULLABLE.
|
length |
Maximum possible column sizes. |
max_length |
Maximum column sizes actually present in result. |
NAME |
Column names. |
NUM_OF_FIELDS |
Number of fields returned. |
table |
Table names in returned set. |
type |
All column types. |
The Perl methods are described in more detail in the following sections. Variables used for method return values have these meanings:
$dbh
$sth
$rc
$rv
Portable DBI Methods
connect($data_source, $username, $password)
connect
method to make a database connection to the data source. The
$data_source value should begin with
DBI:driver_name:. Example uses of connect with the
DBD::mysql driver: $dbh = DBI->connect("DBI:mysql:$database", $user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname",
$user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname:$port",
$user, $password);
If the user name and/or password are undefined, DBI uses
the values of the DBI_USER and DBI_PASS environment
variables, respectively. If you don't specify a hostname, it defaults to
'localhost'. If you don't specify a port number, it defaults to
the default MySQL port (3306 ). As of Msql-Mysql-modules Version
1.2009, the $data_source value allows certain modifiers:
mysql_read_default_file=file_name
mysql_read_default_group=group_name
[client] group. By specifying the
mysql_read_default_group option, the default group becomes the
[group_name] group.
mysql_compression=1
mysql_socket=/path/to/socket
DBI script, you can
take them from the user's `~/.my.cnf' option file instead by writing
your connect call like this: $dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf",
$user, $password);
This call will read options defined for the [client] group
in the option file. If you wanted to do the same thing but use options
specified for the [perl] group as well, you could use this: $dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf"
. ";mysql_read_default_group=perl",
$user, $password);
disconnect
disconnect method disconnects the database handle from
the database. This is typically called right before you exit from the program.
Example: $rc = $dbh->disconnect;
prepare($statement)
($sth), which you can use to invoke the
execute method. Typically you handle SELECT
statements (and SELECT-like statements such as SHOW,
DESCRIBE, and EXPLAIN) by means of
prepare and execute. Example: $sth = $dbh->prepare($statement)
or die "Can't prepare $statement: $dbh->errstr\n";
execute
execute method executes a prepared statement. For
non-SELECT statements, execute returns the number of
rows affected. If no rows are affected, execute returns
"0E0", which Perl treats as zero but regards as true. If an error
occurs, execute returns undef. For
SELECT statements, execute only starts the SQL query
in the database; you need to use one of the fetch_* methods
described below to retrieve the data. Example: $rv = $sth->execute
or die "can't execute the query: $sth->errstr;
do($statement)
do method prepares and executes a SQL statement and
returns the number of rows affected. If no rows are affected, do
returns "0E0", which Perl treats as zero but regards as true.
This method is generally used for non-SELECT statements that
cannot be prepared in advance (due to driver limitations) or that do not need
to be executed more than once (inserts, deletes, etc.). Example: $rv = $dbh->do($statement)
or die "Can't execute $statement: $dbh- >errstr\n";
Generally the 'do' statement is much faster (and is preferable) than
prepare/execute for statements that don't contain parameters.
quote($string)
quote method is used to "escape" any special characters
contained in the string and to add the required outer quotation marks.
Example: $sql = $dbh->quote($string)
fetchrow_array
while(@row = $sth->fetchrow_array) {
print qw($row[0]\t$row[1]\t$row[2]\n);
}
fetchrow_arrayref
while($row_ref = $sth->fetchrow_arrayref) {
print qw($row_ref->[0]\t$row_ref->[1]\t$row_ref->[2]\n);
}
fetchrow_hashref
while($hash_ref = $sth->fetchrow_hashref) {
print qw($hash_ref->{firstname}\t$hash_ref->{lastname}\t\
$hash_ref- > title}\n);
}
fetchall_arrayref
my $table = $sth->fetchall_arrayref
or die "$sth->errstr\n";
my($i, $j);
for $i ( 0 .. $#{$table} ) {
for $j ( 0 .. $#{$table->[$i]} ) {
print "$table->[$i][$j]\t";
}
print "\n";
}
finish
$rc = $sth->finish;
rows
SELECT
execute statement. Example: $rv = $sth->rows;
NULLABLE
NULL values. Example: $null_possible = $sth->{NULLABLE};
NUM_OF_FIELDS
SELECT or SHOW FIELDS statement. You may use this
for checking whether a statement returned a result: A zero value indicates a
non-SELECT statement like INSERT,
DELETE, or UPDATE. Example: $nr_of_fields = $sth->{NUM_OF_FIELDS};
data_sources($driver_name)
'localhost'. Example: @dbs = DBI->data_sources("mysql");
ChopBlanks
fetchrow_* methods will
chop leading and trailing blanks from the returned values. Example: $sth->{'ChopBlanks'} =1;
trace($trace_level)
trace($trace_level, $trace_filename)
trace method enables or disables tracing. When invoked as
a DBI class method, it affects tracing for all handles. When
invoked as a database or statement handle method, it affects tracing for the
given handle (and any future children of the handle). Setting
$trace_level to 2 provides detailed trace information. Setting
$trace_level to 0 disables tracing. Trace output goes to the
standard error output by default. If $trace_filename is
specified, the file is opened in append mode and output for all
traced handles is written to that file. Example: DBI->trace(2); # trace everything
DBI->trace(2,"/tmp/dbi.out"); # trace everything to
# /tmp/dbi.out
$dth->trace(2); # trace this database handle
$sth->trace(2); # trace this statement handle
You can also enable
DBI tracing by setting the DBI_TRACE environment
variable. Setting it to a numeric value is equivalent to calling
DBI->(value). Setting it to a pathname is equivalent to
calling DBI->(2,value). MySQL-specific Methods
The methods shown below are MySQL-specific and not part of the
DBI standard. Several of them are now deprecated:
is_blob, is_key, is_num,
is_pri_key, is_not_null, length,
max_length, and table. Where DBI-standard
alternatives exist, they are noted below:
insertid
AUTO_INCREMENT feature of MySQL, the new auto-incremented values
will be stored here. Example: $new_id = $sth->{insertid};
As an alternative, you can use $dbh->{'mysql_insertid'}.
is_blob
BLOB. Example: $keys = $sth->{is_blob};
is_key
$keys = $sth->{is_key};
is_num
$nums = $sth->{is_num};
is_pri_key
$pri_keys = $sth->{is_pri_key};
is_not_null
NULL values. Example: $not_nulls = $sth->{is_not_null};
is_not_null is deprecated; it is preferable to use the
NULLABLE attribute (described above), because that is a DBI
standard.
length
max_length
length array indicates the maximum possible sizes that each
column may be (as declared in the table description). The
max_length array indicates the maximum sizes actually present in
the result table. Example: $lengths = $sth->{length};
$max_lengths = $sth->{max_length};
NAME
$names = $sth->{NAME};
table
$tables = $sth->{table};
type
$types = $sth->{type};
DBI/DBD InformationYou can use the perldoc command to get more information about
DBI.
perldoc DBI perldoc DBI::FAQ perldoc DBD::mysql
You can also use the pod2man, pod2html, etc., tools
to translate to other formats.
You can find the latest DBI information at the DBI
Web page:
http://www.symbolstone.org/technology/perl/DBI/
MySQL provides support for ODBC by means of the MyODBC program. This chapter will teach you how to install MyODBC, and how to use it. Here, you will also find a list of common programs that are known to work with MyODBC.
MyODBC is a 32-bit ODBC (2.50) level 0 (with level 1 and level 2 features) driver for connecting an ODBC-aware application to MySQL. MyODBC works on Windows95, Windows98, NT, 2000 and on most Unix platforms.
MyODBC is in public domain, and you can find the newest version at http://mysql.com/downloads/api-myodbc.html.
If you have problem with MyODBC and your program also works with OLEDB, you should try the OLEDB driver.
Normally you only need to install MyODBC on Windows machines. You only need MyODBC for Unix if you have a program like ColdFusion that is running on the Unix machine and uses ODBC to connect to the databases.
If you want to install MyODBC on a Unix box, you will also need an ODBC manager. MyODBC is known to work with most of the Unix ODBC managers. See section 1.6.1 MySQL Portals.
To install MyODBC on Windows, you should download the
appropriate MyODBC .zip file (for Windows or NT/Win2000),
unpack it with WINZIP, or some similar program, and execute the
SETUP.EXE file.
On Windows/NT you may get the following error when trying to install MyODBC:
An error occurred while copying C:\WINDOWS\SYSTEM\MFC30.DLL. Restart Windows and try installing again (before running any applications which use ODBC)
The problem in this case is that some other program is using ODBC and because
of how Windows is designed, you may not in this case be able to install a new
ODBC drivers with Microsoft's ODBC setup program. In most cases you can continue
by just pressing Ignore to copy the rest of the MyODBC files and
the final installation should still work. If this doesn't work, the solution is
to reboot your computer in ``safe mode`` (Choose this by pressing F8 just before
your machine starts Windows during rebooting), install MyODBC,
and reboot to normal mode.
GRANT
command. See section 4.3.1
GRANT and REVOKE Syntax.
Notice that there are other configuration options on the screen of MySQL (trace, don't prompt on connect, etc) that you can try if you run into problems.
There are three possibilities for specifying the server name on Windows95:
ip hostnameFor example:
194.216.84.21 my_hostname
Example of how to fill in the ODBC setup:
Windows DSN name: test Description: This is my test database MySql Database: test Server: 194.216.84.21 User: monty Password: my_password Port:
The value for the Windows DSN name field is any name that is
unique in your Windows ODBC setup.
You don't have to specify values for the Server,
User, Password, or Port fields in the
ODBC setup screen. However, if you do, the values will be used as the defaults
later when you attempt to make a connection. You have the option of changing the
values at that time.
If the port number is not given, the default port (3306 ) is used.
If you specify the option Read options from C:\my.cnf, the
groups client and odbc will be read from the
`C:\my.cnf' file. You can use all options that are usable by
mysql_options(). See section 8.4.3.159
mysql_options().
One can specify the following parameters for MyODBC on the
[Servername] section of an ODBC.INI file or through
the InConnectionString argument in the
SQLDriverConnect() call.
| Parameter | Default value | Comment |
| user | ODBC (on Windows) | The username used to connect to MySQL. |
| server | localhost | The hostname of the MySQL server. |
| database | The default database | |
| option | 0 | A integer by which you can specify how MyODBC should work. See below. |
| port | 3306 | The TCP/IP port to use if server is not
localhost. |
| stmt | A statement that will be executed when connection to
MySQL. | |
| password | The password for the server user
combination. | |
| socket | The socket or Windows pipe to connect to. |
The option argument is used to tell MyODBC that the client isn't 100% ODBC compliant. On Windows, one normally sets the option flag by toggling the different options on the connection screen but one can also set this in the opton argument. The following options are listed in the same order as they appear in the MyODBC connect screen:
| Bit | Description |
| 1 | The client can't handle that MyODBC returns the real width of a column. |
| 2 | The client can't handle that MySQL returns the true value of affected rows. If this flag is set then MySQL returns 'found rows' instead. One must have MySQL 3.21.14 or newer to get this to work. |
| 4 | Make a debug log in c:\myodbc.log. This is the same as putting
MYSQL_DEBUG=d:t:O,c::\myodbc.log in `AUTOEXEC.BAT'
|
| 8 | Don't set any packet limit for results and parameters. |
| 16 | Don't prompt for questions even if driver would like to prompt |
| 32 | Simulate a ODBC 1.0 driver in some context. |
| 64 | Ignore use of database name in 'database.table.column'. |
| 128 | Force use of ODBC manager cursors (experimental). |
| 256 | Disable the use of extended fetch (experimental). |
| 512 | Pad CHAR fields to full column length. |
| 1024 | SQLDescribeCol() will return fully qualifed column names |
| 2048 | Use the compressed server/client protocol |
| 4096 | Tell server to ignore space after function name and before
'(' (needed by PowerBuilder). This will make all function
names keywords! |
| 8192 | Connect with named pipes to a mysqld server running on
NT. |
| 16384 | Change LONGLONG columns to INT columns (some applications can't handle LONGLONG). |
| 32768 | Return 'user' as Table_qualifier and Table_owner from SQLTables (experimental) |
| 65536 | Read parameters from the client and odbc
groups from `my.cnf' |
| 131072 | Add some extra safety checks (should not bee needed but...) |
If you want to have many options, you should add the above flags! For example setting option to 12 (4+8) gives you debugging without package limits!
The default `MYODBC.DLL' is compiled for optimal performance. If you
want to to debug MyODBC (for example to enable tracing), you
should instead use MYODBCD.DLL. To install this file, copy
`MYODBCD.DLL' over the installed MYODBC.DLL file.
MyODBC has been tested with Access, Admndemo.exe, C++-Builder, Borland Builder 4, Centura Team Developer (formerly Gupta SQL/Windows), ColdFusion (on Solaris and NT with svc pack 5), Crystal Reports, DataJunction, Delphi, ERwin, Excel, iHTML, FileMaker Pro, FoxPro, Notes 4.5/4.6, SBSS, Perl DBD-ODBC, Paradox, Powerbuilder, Powerdesigner 32 bit, VC++, and Visual Basic.
If you know of any other applications that work with MyODBC, please send mail to myodbc@lists.mysql.com about this!
With some programs you may get an error like: Another user has modifies
the record that you have modified. In most cases this can be solved by
doing one of the following things:
If the above doesn't help, you should do a MyODBC trace file and
try to figure out why things go wrong.
Most programs should work with MyODBC, but for each of those listed below, we have tested it ourselves or received confirmation from some user that it works:
Microsoft Data Access
Components) from http://www.microsoft.com/data/.
This will fix the following bug in Access: when you export data to MySQL,
the table and column names aren't specified. Another way to around this bug
is to upgrade to MyODBC Version 2.50.33 and MySQL Version 3.23.x, which
together provide a workaround for this bug! You should also get and apply
the Microsoft Jet 4.0 Service Pack 5 (SP5) which can be found here http://support.microsoft.com/support/kb/articles/Q%20239/1/14.ASP.
This will fix some cases where columns are marked as #deleted#
in Access. Note that if you are using MySQL Version 3.22, you must to apply
the MDAC patch and use MyODBC 2.50.32 or 2.50.34 and above to go around this
problem.
Return matching rows. For Access 2.0, you should additionally
enable Simulate ODBC 1.0.
TIMESTAMP(14) or simple
TIMESTAMP is recommended instead of other
TIMESTAMP(X) variations.
#DELETED#.
DOUBLE float fields. Access fails when comparing
with single floats. The symptom usually is that new or updated rows may show
up as #DELETED# or that you can't find or update rows.
BIGINT
as one of the column, then the results will be displayed as
#DELETED. The work around solution is:
TIMESTAMP as the data
type, preferably TIMESTAMP(14).
'Change BIGINT columns to INT' in connection
options dialog in ODBC DSN Administrator
#DELETED#, but newly
added/updated records will be displayed properly.
Another user has changed your
data after adding a TIMESTAMP column, the following
trick may help you: Don't use table data sheet view. Create
instead a form with the fields you want, and use that form data
sheet view. You should set the DefaultValue property for the
TIMESTAMP column to NOW(). It may be a good idea
to hide the TIMESTAMP column from view so your users are not
confused.
"Query|SQLSpecific|Pass-Through" from the Access menu.
BLOB columns as OLE
OBJECTS. If you want to have MEMO columns instead, you
should change the column to TEXT with ALTER TABLE.
DATE columns properly. If you
have a problem with these, change the columns to DATETIME.
BYTE, Access will
try to export this as TINYINT instead of TINYINT
UNSIGNED. This will give you problems if you have values > 127 in
the column! CursorLocation Property as
adUseServer will return for the RecordCount Property
a result of -1. To have the right value, you need to set this property to
adUseClient, like is showing in the VB code below: Dim myconn As New ADODB.Connection Dim myrs As New Recordset Dim mySQL As String Dim myrows As Long myconn.Open "DSN=MyODBCsample" mySQL = "SELECT * from user" myrs.Source = mySQL Set myrs.ActiveConnection = myconn myrs.CursorLocation = adUseClient myrs.Open myrows = myrs.RecordCount myrs.Close myconn.CloseAnother workaround is to use a
SELECT COUNT(*) statement
for a similar query to get the correct row count.
Return matching rows.
Don't optimize
column widths and Return matching rows.
Active or use
the method Open. Note that Active will start by
automatically issuing a SELECT * FROM ... query that may not be a
good thing if your tables are big!
VARCHAR rather than
ENUM, as it exports the latter in a manner that causes MySQL
grief.
CONCAT() function. For example: select CONCAT(rise_time), CONCAT(set_time)
from sunrise_sunset;
Values retrieved as strings this way should be correctly recognised as
time values by Excel97. The purpose of CONCAT() in this example
is to fool ODBC into thinking the column is of ``string type''. Without the
CONCAT(), ODBC knows the column is of time type, and Excel does
not understand that. Note that this is a bug in Excel, because it
automatically converts a string to a time. This would be great if the source
was a text file, but is plain stupid when the source is an ODBC connection
that reports exact types for each column. MyODBC driver and the Add-in Microsoft Query help. For example,
create a db with a table containing 2 columns of text:
mysql client command-line tool.
Don't optimize column
width option field when connecting to MySQL. Also, here is some
potentially useful Delphi code that sets up both an ODBC entry and a BDE entry
for MyODBC (the BDE entry requires a BDE Alias Editor that is
free at a Delphi Super Page near you. (Thanks to Bryan Brunton bryan@flesherfab.com for this): fReg:= TRegistry.Create;
fReg.OpenKey('\Software\ODBC\ODBC.INI\DocumentsFab', True);
fReg.WriteString('Database', 'Documents');
fReg.WriteString('Description', ' ');
fReg.WriteString('Driver', 'C:\WINNT\System32\myodbc.dll');
fReg.WriteString('Flag', '1');
fReg.WriteString('Password', '');
fReg.WriteString('Port', ' ');
fReg.WriteString('Server', 'xmark');
fReg.WriteString('User', 'winuser');
fReg.OpenKey('\Software\ODBC\ODBC.INI\ODBC Data Sources', True);
fReg.WriteString('DocumentsFab', 'MySQL');
fReg.CloseKey;
fReg.Free;
Memo1.Lines.Add('DATABASE NAME=');
Memo1.Lines.Add('USER NAME=');
Memo1.Lines.Add('ODBC DSN=DocumentsFab');
Memo1.Lines.Add('OPEN MODE=READ/WRITE');
Memo1.Lines.Add('BATCH COUNT=200');
Memo1.Lines.Add('LANGDRIVER=');
Memo1.Lines.Add('MAX ROWS=-1');
Memo1.Lines.Add('SCHEMA CACHE DIR=');
Memo1.Lines.Add('SCHEMA CACHE SIZE=8');
Memo1.Lines.Add('SCHEMA CACHE TIME=-1');
Memo1.Lines.Add('SQLPASSTHRU MODE=SHARED AUTOCOMMIT');
Memo1.Lines.Add('SQLQRYMODE=');
Memo1.Lines.Add('ENABLE SCHEMA CACHE=FALSE');
Memo1.Lines.Add('ENABLE BCD=FALSE');
Memo1.Lines.Add('ROWSET SIZE=20');
Memo1.Lines.Add('BLOBS TO CACHE=64');
Memo1.Lines.Add('BLOB SIZE=32');
AliasEditor.Add('DocumentsFab','MySQL',Memo1.Lines);
Return matching rows.
SHOW PROCESSLIST will not work properly. The fix is to set
add the option OPTION=16834 in the ODBC connect string or set the
Change BIGINT columns to INT option in the MyODBC connect screen.
You may also want to set the Return matching rows option.
[Microsoft][ODBC Driver Manager] Driver does
not support this parameter the reason may be that you have a
BIGINT in your result. Try setting the Change BIGINT
columns to INT option in the MyODBC connect screen.
Don't optimize column widths.
AUTO_INCREMENT Column in ODBCA common problem is how to get the value of an automatically generated ID
from an INSERT. With ODBC, you can do something like this (assuming
that auto is an AUTO_INCREMENT field):
INSERT INTO foo (auto,text) VALUES(NULL,'text'); SELECT LAST_INSERT_ID();
Or, if you are just going to insert the ID into another table, you can do this:
INSERT INTO foo (auto,text) VALUES(NULL,'text'); INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text');
See section 8.4.6.3 How Can I Get the Unique ID for the Last Inserted Row?.
For the benefit of some ODBC applications (at least Delphi and Access), the following query can be used to find a newly inserted row:
SELECT * FROM tbl_name WHERE auto IS NULL;
If you encounter difficulties with MyODBC, you should start by making a log file from the ODBC manager (the log you get when requesting logs from ODBCADMIN) and a MyODBC log.
To get a MyODBC log, you need to do the following:
myodbcd.dll and not
myodbc.dll. The easiest way to do this is to get
myodbcd.dll from the MyODBC distribution and copy it over the
myodbc.dll, which is probably in your
C:\windows\system32 or C:\winnt\system32 directory.
Note that you probably want to restore the old myodbc.dll file when you have
finished testing, as this is a lot faster than myodbcd.dll.
myodbcd.dll driver (see above).
Check the MyODBC trace file, to find out what could be wrong.
You should be able to find out the issued queries by searching after the string
>mysql_real_query in the `myodbc.log' file.
You should also try duplicating the queries in the mysql monitor
or admndemo to find out if the error is MyODBC or MySQL.
If you find out something is wrong, please only send the relevant rows (max 40 rows) to myodbc@lists.mysql.com. Please never send the whole MyODBC or ODBC log file!
If you are unable to find out what's wrong, the last option is to make an archive (tar or zip) that contains a MyODBC trace file, the ODBC log file, and a README file that explains the problem. You can send this to ftp://support.mysql.com/pub/mysql/secret/. Only we at MySQL AB will have access to the files you upload, and we will be very discrete with the data!
If you can create a program that also shows this problem, please upload this too!
If the program works with some other SQL server, you should make an ODBC log file where you do exactly the same thing in the other SQL server.
Remember that the more information you can supply to us, the more likely it is that we can fix the problem!
The C API code is distributed with MySQL. It is included in the
mysqlclient library and allows C programs to access a database.
Many of the clients in the MySQL source distribution are written in C. If you
are looking for examples that demonstrate how to use the C API, take a look at
these clients. You can find these in the clients directory in the
MySQL source distribution.
Most of the other client APIs (all except Java) use the
mysqlclient library to communicate with the MySQL server. This
means that, for example, you can take advantage of many of the same environment
variables that are used by other client programs, because they are referenced
from the library. See section 4.8
MySQL Client-Side Scripts and Utilities, for a list of these variables.
The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16K bytes) is automatically increased up to the maximum size (the maximum is 16M). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets.
The communication buffer must be large enough to contain a single SQL
statement (for client-to-server traffic) and one row of returned data (for
server-to-client traffic). Each thread's communication buffer is dynamically
enlarged to handle any query or row up to the maximum limit. For example, if you
have BLOB values that contain up to 16M of data, you must have a
communication buffer limit of at least 16M (in both server and client). The
client's default maximum is 16M, but the default maximum in the server is 1M.
You can increase this by changing the value of the
max_allowed_packet parameter when the server is started. See
section 5.5.2
Tuning Server Parameters.
The MySQL server shrinks each communication buffer to
net_buffer_length bytes after each query. For clients, the size of
the buffer associated with a connection is not decreased until the connection is
closed, at which time client memory is reclaimed.
For programming with threads, see section 8.4.8 How to Make a Threaded Client. For creating a stand-alone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see section 8.4.9 libmysqld, the Embedded MySQL Server Library.
MYSQL
MYSQL_RES
SELECT, SHOW, DESCRIBE,
EXPLAIN). The information returned from a query is called the
result set in the remainder of this section.
MYSQL_ROW
mysql_fetch_row().
MYSQL_FIELD
MYSQL_FIELD structures for each field by calling
mysql_fetch_field() repeatedly. Field values are not part of this
structure; they are contained in a MYSQL_ROW structure.
MYSQL_FIELD_OFFSET
mysql_field_seek().) Offsets are field numbers within a
row, beginning at zero.
my_ulonglong
mysql_affected_rows(), mysql_num_rows(), and
mysql_insert_id(). This type provides a range of 0
to 1.84e19. On some systems, attempting to print a value of type
my_ulonglong will not work. To print such a value, convert it to
unsigned long and use a %lu print format. Example: printf (Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));
The MYSQL_FIELD structure contains the members listed below:
char * name
char * table
table value is an empty string.
char * def
mysql_list_fields().
enum enum_field_types type
type value may be one of the
following:
| Type value | Type description |
FIELD_TYPE_TINY |
TINYINT field |
FIELD_TYPE_SHORT |
SMALLINT field |
FIELD_TYPE_LONG |
INTEGER field |
FIELD_TYPE_INT24 |
MEDIUMINT field |
FIELD_TYPE_LONGLONG |
BIGINT field |
FIELD_TYPE_DECIMAL |
DECIMAL or NUMERIC field |
FIELD_TYPE_FLOAT |
FLOAT field |
FIELD_TYPE_DOUBLE |
DOUBLE or REAL field |
FIELD_TYPE_TIMESTAMP |
TIMESTAMP field |
FIELD_TYPE_DATE |
DATE field |
FIELD_TYPE_TIME |
TIME field |
FIELD_TYPE_DATETIME |
DATETIME field |
FIELD_TYPE_YEAR |
YEAR field |
FIELD_TYPE_STRING |
String (CHAR or VARCHAR) field |
FIELD_TYPE_BLOB |
BLOB or TEXT field (use
max_length to determine the maximum length) |
FIELD_TYPE_SET |
SET field |
FIELD_TYPE_ENUM |
ENUM field |
FIELD_TYPE_NULL |
NULL-type field |
FIELD_TYPE_CHAR |
Deprecated; use FIELD_TYPE_TINY instead
|
IS_NUM() macro to test
whether or not a field has a numeric type. Pass the type value to
IS_NUM() and it will evaluate to TRUE if the field is numeric: if (IS_NUM(field->type))
printf("Field is numeric\n");
unsigned int length
unsigned int max_length
mysql_store_result() or mysql_list_fields(), this
contains the maximum length for the field. If you use
mysql_use_result(), the value of this variable is zero.
unsigned int flags
flags value may have
zero or more of the following bits set:
| Flag value | Flag description |
NOT_NULL_FLAG |
Field can't be NULL |
PRI_KEY_FLAG |
Field is part of a primary key |
UNIQUE_KEY_FLAG |
Field is part of a unique key |
MULTIPLE_KEY_FLAG |
Field is part of a non-unique key |
UNSIGNED_FLAG |
Field has the UNSIGNED attribute |
ZEROFILL_FLAG |
Field has the ZEROFILL attribute |
BINARY_FLAG |
Field has the BINARY attribute |
AUTO_INCREMENT_FLAG |
Field has the AUTO_INCREMENT attribute |
ENUM_FLAG |
Field is an ENUM (deprecated) |
BLOB_FLAG |
Field is a BLOB or TEXT (deprecated)
|
TIMESTAMP_FLAG |
Field is a TIMESTAMP (deprecated)
|
BLOB_FLAG,
ENUM_FLAG, and TIMESTAMP_FLAG flags is deprecated
because they indicate the type of a field rather than an attribute of its
type. It is preferable to test field->type against
FIELD_TYPE_BLOB, FIELD_TYPE_ENUM, or
FIELD_TYPE_TIMESTAMP instead. The example below illustrates a
typical use of the flags value: if (field->flags & NOT_NULL_FLAG)
printf("Field can't be null\n");
You may use the following convenience macros to determine the boolean
status of the flags value:
| Flag status | Description |
IS_NOT_NULL(flags) |
True if this field is defined as NOT NULL |
IS_PRI_KEY(flags) |
True if this field is a primary key |
IS_BLOB(flags) |
True if this field is a BLOB or TEXT
(deprecated; test field->type instead)
|
unsigned int decimals
The functions available in the C API are listed below and are described in greater detail in the next section. See section 8.4.3 C API Function Descriptions.
| Function | Description |
| mysql_affected_rows() | Returns the number of rows changed/deleted/inserted by the last
UPDATE, DELETE, or INSERT query.
|
| mysql_close() | Closes a server connection. |
| mysql_connect() | Connects to a MySQL server. This function is deprecated; use
mysql_real_connect() instead. |
| mysql_change_user() | Changes user and database on an open connection. |
| mysql_character_set_name() | Returns the name of the default character set for the connection. |
| mysql_create_db() | Creates a database. This function is deprecated; use the SQL command
CREATE DATABASE instead. |
| mysql_data_seek() | Seeks to an arbitrary row in a query result set. |
| mysql_debug() | Does a DBUG_PUSH with the given string. |
| mysql_drop_db() | Drops a database. This function is deprecated; use the SQL command
DROP DATABASE instead. |
| mysql_dump_debug_info() | Makes the server write debug information to the log. |
| mysql_eof() | Determines whether or not the last row of a result set has been read.
This function is deprecated; mysql_errno() or
mysql_error() may be used instead. |
| mysql_errno() | Returns the error number for the most recently invoked MySQL function. |
| mysql_error() | Returns the error message for the most recently invoked MySQL function. |
| mysql_real_escape_string() | Escapes special characters in a string for use in a SQL statement taking into account the current charset of the connection. |
| mysql_escape_string() | Escapes special characters in a string for use in a SQL statement. |
| mysql_fetch_field() | Returns the type of the next table field. |
| mysql_fetch_field_direct() | Returns the type of a table field, given a field number. |
| mysql_fetch_fields() | Returns an array of all field structures. |
| mysql_fetch_lengths() | Returns the lengths of all columns in the current row. |
| mysql_fetch_row() | Fetches the next row from the result set. |
| mysql_field_seek() | Puts the column cursor on a specified column. |
| mysql_field_count() | Returns the number of result columns for the most recent query. |
| mysql_field_tell() | Returns the position of the field cursor used for the last
mysql_fetch_field(). |
| mysql_free_result() | Frees memory used by a result set. |
| mysql_get_client_info() | Returns client version information. |
| mysql_get_host_info() | Returns a string describing the connection. |
| mysql_get_proto_info() | Returns the protocol version used by the connection. |
| mysql_get_server_info() | Returns the server version number. |
| mysql_info() | Returns information about the most recently executed query. |
| mysql_init() | Gets or initialises a MYSQL structure. |
| mysql_insert_id() | Returns the ID generated for an AUTO_INCREMENT column by
the previous query. |
| mysql_kill() | Kills a given thread. |
| mysql_list_dbs() | Returns database names matching a simple regular expression. |
| mysql_list_fields() | Returns field names matching a simple regular expression. |
| mysql_list_processes() | Returns a list of the current server threads. |
| mysql_list_tables() | Returns table names matching a simple regular expression. |
| mysql_num_fields() | Returns the number of columns in a result set. |
| mysql_num_rows() | Returns the number of rows in a result set. |
| mysql_options() | Sets connect options for mysql_connect(). |
| mysql_ping() | Checks whether or not the connection to the server is working, reconnecting as necessary. |
| mysql_query() | Executes a SQL query specified as a null-terminated string. |
| mysql_real_connect() | Connects to a MySQL server. |
| mysql_real_query() | Executes a SQL query specified as a counted string. |
| mysql_reload() | Tells the server to reload the grant tables. |
| mysql_row_seek() | Seeks to a row in a result set, using value returned from
mysql_row_tell(). |
| mysql_row_tell() | Returns the row cursor position. |
| mysql_select_db() | Selects a database. |
| mysql_shutdown() | Shuts down the database server. |
| mysql_stat() | Returns the server status as a string. |
| mysql_store_result() | Retrieves a complete result set to the client. |
| mysql_thread_id() | Returns the current thread ID. |
| mysql_thread_safe() | Returns 1 if the clients are compiled as thread safe. |
| mysql_use_result() | Initiates a row-by-row result set retrieval. |
To connect to the server, call mysql_init() to initialise a
connection handler, then call mysql_real_connect() with that
handler (along with other information such as the hostname, user name, and
password). Upon connection, mysql_real_connect() sets the
reconnect flag (part of the MYSQL structure) to a value of
1. This flag indicates, in the event that a query cannot be
performed because of a lost connection, to try reconnecting to the server before
giving up. When you are done with the connection, call
mysql_close() to terminate it.
While a connection is active, the client may send SQL queries to the server
using mysql_query() or mysql_real_query(). The
difference between the two is that mysql_query() expects the query
to be specified as a null-terminated string whereas
mysql_real_query() expects a counted string. If the string contains
binary data (which may include null bytes), you must use
mysql_real_query().
For each non-SELECT query (for example, INSERT,
UPDATE, DELETE), you can find out how many rows were
changed (affected) by calling mysql_affected_rows().
For SELECT queries, you retrieve the selected rows as a result
set. (Note that some statements are SELECT-like in that they return
rows. These include SHOW, DESCRIBE, and
EXPLAIN. They should be treated the same way as SELECT
statements.)
There are two ways for a client to process result sets. One way is to
retrieve the entire result set all at once by calling
mysql_store_result(). This function acquires from the server all
the rows returned by the query and stores them in the client. The second way is
for the client to initiate a row-by-row result set retrieval by calling
mysql_use_result(). This function initialises the retrieval, but
does not actually get any rows from the server.
In both cases, you access rows by calling mysql_fetch_row().
With mysql_store_result(), mysql_fetch_row() accesses
rows that have already been fetched from the server. With
mysql_use_result(), mysql_fetch_row() actually
retrieves the row from the server. Information about the size of the data in
each row is available by calling mysql_fetch_lengths().
After you are done with a result set, call mysql_free_result()
to free the memory used for it.
The two retrieval mechanisms are complementary. Client programs should choose
the approach that is most appropriate for their requirements. In practice,
clients tend to use mysql_store_result() more commonly.
An advantage of mysql_store_result() is that because the rows
have all been fetched to the client, you not only can access rows sequentially,
you can move back and forth in the result set using
mysql_data_seek() or mysql_row_seek() to change the
current row position within the result set. You can also find out how many rows
there are by calling mysql_num_rows(). On the other hand, the
memory requirements for mysql_store_result() may be very high for
large result sets and you are more likely to encounter out-of-memory conditions.
An advantage of mysql_use_result() is that the client requires
less memory for the result set because it maintains only one row at a time (and
because there is less allocation overhead, mysql_use_result() can
be faster). Disadvantages are that you must process each row quickly to avoid
tying up the server, you don't have random access to rows within the result set
(you can only access rows sequentially), and you don't know how many rows are in
the result set until you have retrieved them all. Furthermore, you must
retrieve all the rows even if you determine in mid-retrieval that you've found
the information you were looking for.
The API makes it possible for clients to respond appropriately to queries
(retrieving rows only as necessary) without knowing whether or not the query is
a SELECT. You can do this by calling
mysql_store_result() after each mysql_query() (or
mysql_real_query()). If the result set call succeeds, the query was
a SELECT and you can read the rows. If the result set call fails,
call mysql_field_count() to determine whether or not a result was
actually to be expected. If mysql_field_count() returns zero, the
query returned no data (indicating that it was an INSERT,
UPDATE, DELETE, etc.), and was not expected to return
rows. If mysql_field_count() is non-zero, the query should have
returned rows, but didn't. This indicates that the query was a
SELECT that failed. See the description for
mysql_field_count() for an example of how this can be done.
Both mysql_store_result() and mysql_use_result()
allow you to obtain information about the fields that make up the result set
(the number of fields, their names and types, etc.). You can access field
information sequentially within the row by calling
mysql_fetch_field() repeatedly, or by field number within the row
by calling mysql_fetch_field_direct(). The current field cursor
position may be changed by calling mysql_field_seek(). Setting the
field cursor affects subsequent calls to mysql_fetch_field(). You
can also get information for fields all at once by calling
mysql_fetch_fields().
For detecting and reporting errors, MySQL provides access to error
information by means of the mysql_errno() and
mysql_error() functions. These return the error code or error
message for the most recently invoked function that can succeed or fail,
allowing you to determine when an error occurred and what it was.
In the descriptions below, a parameter or return value of NULL
means NULL in the sense of the C programming language, not a MySQL
NULL value.
Functions that return a value generally return a pointer or an integer.
Unless specified otherwise, functions returning a pointer return a
non-NULL value to indicate success or a NULL value to
indicate an error, and functions returning an integer return zero to indicate
success or non-zero to indicate an error. Note that ``non-zero'' means just
that. Unless the function description says otherwise, do not test against a
value other than zero:
if (result) /* correct */
... error ...
if (result < 0) /* incorrect */
... error ...
if (result == -1) /* incorrect */
... error ...
When a function returns an error, the Errors subsection of
the function description lists the possible types of errors. You can find out
which of these occurred by calling mysql_errno(). A string
representation of the error may be obtained by calling
mysql_error().
mysql_affected_rows()my_ulonglong mysql_affected_rows(MYSQL *mysql)
Returns the number of rows changed by the last UPDATE, deleted
by the last DELETE or inserted by the last INSERT
statement. May be called immediately after mysql_query() for
UPDATE, DELETE, or INSERT statements. For
SELECT statements, mysql_affected_rows() works like
mysql_num_rows().
An integer greater than zero indicates the number of rows affected or
retrieved. Zero indicates that no records where updated for an
UPDATE statement, no rows matched the WHERE clause in
the query or that no query has yet been executed. -1 indicates that the query
returned an error or that, for a SELECT query,
mysql_affected_rows() was called prior to calling
mysql_store_result().
None.
mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%ld products updated",(long) mysql_affected_rows(&mysql));
If one specifies the flag CLIENT_FOUND_ROWS when connecting to
mysqld, mysql_affected_rows() will return the number
of rows matched by the WHERE statement for UPDATE
statements.
Note that when one uses a REPLACE command,
mysql_affected_rows() will return 2 if the new row replaced and old
row. This is because in this case one row was inserted and then the duplicate
was deleted.
mysql_close()void mysql_close(MYSQL *mysql)
Closes a previously opened connection. mysql_close() also
deallocates the connection handle pointed to by mysql if the handle
was allocated automatically by mysql_init() or
mysql_connect().
None.
None.
mysql_connect()MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user,
const char *passwd)
This function is deprecated. It is preferable to use
mysql_real_connect() instead.
mysql_connect() attempts to establish a connection to a MySQL
database engine running on host. mysql_connect() must
complete successfully before you can execute any of the other API functions,
with the exception of mysql_get_client_info().
The meanings of the parameters are the same as for the corresponding
parameters for mysql_real_connect() with the difference that the
connection parameter may be NULL. In this case the C API allocates
memory for the connection structure automatically and frees it when you call
mysql_close(). The disadvantage of this approach is that you can't
retrieve an error message if the connection fails. (To get error information
from mysql_errno() or mysql_error(), you must provide
a valid MYSQL pointer.)
Same as for mysql_real_connect().
Same as for mysql_real_connect().
mysql_change_user()my_bool mysql_change_user(MYSQL *mysql, const char *user, const char
*password, const char *db)
Changes the user and causes the database specified by db to
become the default (current) database on the connection specified by
mysql. In subsequent queries, this database is the default for
table references that do not include an explicit database specifier.
This function was introduced in MySQL Version 3.23.3.
mysql_change_user() fails unless the connected user can be
authenticated or if he doesn't have permission to use the database. In this case
the user and database are not changed
The db parameter may be set to NULL if you don't
want to have a default database.
Zero for success. Non-zero if an error occurred.
The same that you can get from mysql_real_connect().
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
ER_UNKNOWN_COM_ERROR
ER_ACCESS_DENIED_ERROR
ER_BAD_DB_ERROR
ER_DBACCESS_DENIED_ERROR
ER_WRONG_DB_NAME
if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
fprintf(stderr, "Failed to change user. Error: %s\n",
mysql_error(&mysql));
}
mysql_character_set_name()const char *mysql_character_set_name(MYSQL *mysql)
Returns the default character set for the current connection.
The default character set
None.
mysql_create_db()int mysql_create_db(MYSQL *mysql, const char *db)
Creates the database named by the db parameter.
This function is deprecated. It is preferable to use
mysql_query() to issue a SQL CREATE DATABASE statement
instead.
Zero if the database was created successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_create_db(&mysql, "my_database"))
{
fprintf(stderr, "Failed to create new database. Error: %s\n",
mysql_error(&mysql));
}
mysql_data_seek()void mysql_data_seek(MYSQL_RES *result, unsigned long long
offset)
Seeks to an arbitrary row in a query result set. This requires that the
result set structure contains the entire result of the query, so
mysql_data_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value in the range from 0 to
mysql_num_rows(result)-1.
None.
None.
mysql_debug()void mysql_debug(char *debug)
Does a DBUG_PUSH with the given string.
mysql_debug() uses the Fred Fish debug library. To use this
function, you must compile the client library to support debugging. See section
E.1
Debugging a MySQL server. See section E.2
Debugging a MySQL client.
None.
None.
The call shown below causes the client library to generate a trace file in `/tmp/client.trace' on the client machine:
mysql_debug("d:t:O,/tmp/client.trace");
mysql_drop_db()int mysql_drop_db(MYSQL *mysql, const char *db)
Drops the database named by the db parameter.
This function is deprecated. It is preferable to use
mysql_query() to issue a SQL DROP DATABASE statement
instead.
Zero if the database was dropped successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_drop_db(&mysql, "my_database"))
fprintf(stderr, "Failed to drop the database: Error: %s\n",
mysql_error(&mysql));
mysql_dump_debug_info()int mysql_dump_debug_info(MYSQL *mysql)
Instructs the server to write some debug information to the log. The connected user must have the process privilege for this to work.
Zero if the command was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_eof()my_bool mysql_eof(MYSQL_RES *result)
This function is deprecated. mysql_errno() or
mysql_error() may be used instead.
mysql_eof() determines whether or not the last row of a result
set has been read.
If you acquire a result set from a successful call to
mysql_store_result(), the client receives the entire set in one
operation. In this case, a NULL return from
mysql_fetch_row() always means the end of the result set has been
reached and it is unnecessary to call mysql_eof().
On the other hand, if you use mysql_use_result() to initiate a
result set retrieval, the rows of the set are obtained from the server one by
one as you call mysql_fetch_row() repeatedly. Because an error may
occur on the connection during this process, a NULL return value
from mysql_fetch_row() does not necessarily mean the end of the
result set was reached normally. In this case, you can use
mysql_eof() to determine what happened. mysql_eof()
returns a non-zero value if the end of the result set was reached and zero if an
error occurred.
Historically, mysql_eof() predates the standard MySQL error
functions mysql_errno() and mysql_error(). Because
those error functions provide the same information, their use is preferred over
mysql_eof(), which is now deprecated. (In fact, they provide more
information, because mysql_eof() returns only a boolean value
whereas the error functions indicate a reason for the error when one occurs.)
Zero if no error occurred. Non-zero if the end of the result set has been reached.
None.
The following example shows how you might use mysql_eof():
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(!mysql_eof(result)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
However, you can achieve the same effect with the standard MySQL error functions:
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(mysql_errno(&mysql)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
mysql_errno()unsigned int mysql_errno(MYSQL *mysql)
For the connection specified by mysql,
mysql_errno() returns the error code for the most recently invoked
API function that can succeed or fail. A return value of zero means that no
error occurred. Client error message numbers are listed in the MySQL
`errmsg.h' header file. Server error message numbers are listed in
`mysqld_error.h'. In the MySQL source distribution you can find a
complete list of error messages and error numbers in the file
`Docs/mysqld_error.txt'.
An error code value. Zero if no error occurred.
None.
mysql_error()char *mysql_error(MYSQL *mysql)
For the connection specified by mysql,
mysql_error() returns the error message for the most recently
invoked API function that can succeed or fail. An empty string ("")
is returned if no error occurred. This means the following two tests are
equivalent:
if(mysql_errno(&mysql))
{
// an error occurred
}
if(mysql_error(&mysql)[0] != '\0')
{
// an error occurred
}
The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages. See section 4.6.2 Non-English Error Messages.
A character string that describes the error. An empty string if no error occurred.
None.
mysql_escape_string()You should use mysql_real_escape_string() instead!
This is identical to mysql_real_escape_string() except that it
takes the connection as the first argument.
mysql_real_escape_string() will escape the string according to the
current character set while mysql_escape_string() does not respect
the current charset setting.
mysql_fetch_field()MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)
Returns the definition of one column of a result set as a
MYSQL_FIELD structure. Call this function repeatedly to retrieve
information about all columns in the result set.
mysql_fetch_field() returns NULL when no more fields
are left.
mysql_fetch_field() is reset to return information about the
first field each time you execute a new SELECT query. The field
returned by mysql_fetch_field() is also affected by calls to
mysql_field_seek().
If you've called mysql_query() to perform a SELECT
on a table but have not called mysql_store_result(), MySQL returns
the default blob length (8K bytes) if you call mysql_fetch_field()
to ask for the length of a BLOB field. (The 8K size is chosen
because MySQL doesn't know the maximum length for the BLOB. This
should be made configurable sometime.) Once you've retrieved the result set,
field->max_length contains the length of the largest value for
this column in the specific query.
The MYSQL_FIELD structure for the current column.
NULL if no columns are left.
None.
MYSQL_FIELD *field;
while((field = mysql_fetch_field(result)))
{
printf("field name %s\n", field->name);
}
mysql_fetch_fields()MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)
Returns an array of all MYSQL_FIELD structures for a result set.
Each structure provides the field definition for one column of the result set.
An array of MYSQL_FIELD structures for all columns of a result
set.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;
num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
printf("Field %u is %s\n", i, fields[i].name);
}
mysql_fetch_field_direct()MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int
fieldnr)
Given a field number fieldnr for a column within a result set,
returns that column's field definition as a MYSQL_FIELD structure.
You may use this function to retrieve the definition for an arbitrary column.
The value of fieldnr should be in the range from 0 to
mysql_num_fields(result)-1.
The MYSQL_FIELD structure for the specified column.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;
num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
field = mysql_fetch_field_direct(result, i);
printf("Field %u is %s\n", i, field->name);
}
mysql_fetch_lengths()unsigned long *mysql_fetch_lengths(MYSQL_RES *result)
Returns the lengths of the columns of the current row within a result set. If
you plan to copy field values, this length information is also useful for
optimisation, because you can avoid calling strlen(). In addition,
if the result set contains binary data, you must use this function to
determine the size of the data, because strlen() returns incorrect
results for any field containing null characters.
The length for empty columns and for columns containing NULL
values is zero. To see how to distinguish these two cases, see the description
for mysql_fetch_row().
An array of unsigned long integers representing the size of each column (not
including any terminating null characters). NULL if an error
occurred.
mysql_fetch_lengths() is valid only for the current row of the
result set. It returns NULL if you call it before calling
mysql_fetch_row() or after retrieving all rows in the result.
MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;
row = mysql_fetch_row(result);
if (row)
{
num_fields = mysql_num_fields(result);
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("Column %u is %lu bytes in length.\n", i, lengths[i]);
}
}
mysql_fetch_row()MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)
Retrieves the next row of a result set. When used after
mysql_store_result(), mysql_fetch_row() returns
NULL when there are no more rows to retrieve. When used after
mysql_use_result(), mysql_fetch_row() returns
NULL when there are no more rows to retrieve or if an error
occurred.
The number of values in the row is given by
mysql_num_fields(result). If row holds the return
value from a call to mysql_fetch_row(), pointers to the values are
accessed as row[0] to row[mysql_num_fields(result)-1].
NULL values in the row are indicated by NULL pointers.
The lengths of the field values in the row may be obtained by calling
mysql_fetch_lengths(). Empty fields and fields containing
NULL both have length 0; you can distinguish these by checking the
pointer for the field value. If the pointer is NULL, the field is
NULL; otherwise the field is empty.
A MYSQL_ROW structure for the next row. NULL if
there are no more rows to retrieve or if an error occurred.
CR_SERVER_LOST
CR_UNKNOWN_ERROR
MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;
num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
unsigned long *lengths;
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("[%.*s] ", (int) lengths[i], row[i] ? row[i] : "NULL");
}
printf("\n");
}
mysql_field_count()unsigned int mysql_field_count(MYSQL *mysql)
If you are using a version of MySQL earlier than Version 3.22.24, you should
use unsigned int mysql_num_fields(MYSQL *mysql) instead.
Returns the number of columns for the most recent query on the connection.
The normal use of this function is when mysql_store_result()
returned NULL (and thus you have no result set pointer). In this
case, you can call mysql_field_count() to determine whether or not
mysql_store_result() should have produced a non-empty result. This
allows the client program to take proper action without knowing whether or not
the query was a SELECT (or SELECT-like) statement. The
example shown below illustrates how this may be done.
See section 8.4.6.1
Why Is It that After mysql_query() Returns Success,
mysql_store_result() Sometimes Returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if(mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
else // mysql_store_result() should have returned data
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
}
}
An alternative is to replace the mysql_field_count(&mysql)
call with mysql_errno(&mysql). In this case, you are checking
directly for an error from mysql_store_result() rather than
inferring from the value of mysql_field_count() whether or not the
statement was a SELECT.
mysql_field_seek()MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result,
MYSQL_FIELD_OFFSET offset)
Sets the field cursor to the given offset. The next call to
mysql_fetch_field() will retrieve the field definition of the
column associated with that offset.
To seek to the beginning of a row, pass an offset value of zero.
The previous value of the field cursor.
None.
mysql_field_tell()MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)
Returns the position of the field cursor used for the last
mysql_fetch_field(). This value can be used as an argument to
mysql_field_seek().
The current offset of the field cursor.
None.
mysql_free_result()void mysql_free_result(MYSQL_RES *result)
Frees the memory allocated for a result set by
mysql_store_result(), mysql_use_result(),
mysql_list_dbs(), etc. When you are done with a result set, you
must free the memory it uses by calling mysql_free_result().
None.
None.
mysql_get_client_info()char *mysql_get_client_info(void)
Returns a string that represents the client library version.
A character string that represents the MySQL client library version.
None.
mysql_get_host_info()char *mysql_get_host_info(MYSQL *mysql)
Returns a string describing the type of connection in use, including the server host name.
A character string representing the server host name and the connection type.
None.
mysql_get_proto_info()unsigned int mysql_get_proto_info(MYSQL *mysql)
Returns the protocol version used by current connection.
An unsigned integer representing the protocol version used by the current connection.
None.
mysql_get_server_info()char *mysql_get_server_info(MYSQL *mysql)
Returns a string that represents the server version number.
A character string that represents the server version number.
None.
mysql_info()char *mysql_info(MYSQL *mysql)
Retrieves a string providing information about the most recently executed
query, but only for the statements listed below. For other statements,
mysql_info() returns NULL. The format of the string
varies depending on the type of query, as described below. The numbers are
illustrative only; the string will contain values appropriate for the query.
INSERT INTO ... SELECT ...
Records: 100 Duplicates: 0 Warnings: 0
INSERT INTO ... VALUES (...),(...),(...)...
Records: 3 Duplicates: 0 Warnings: 0
LOAD DATA INFILE ...
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
ALTER TABLE
Records: 3 Duplicates: 0 Warnings: 0
UPDATE
Rows matched: 40 Changed: 40 Warnings: 0
Note that mysql_info() returns a non-NULL value for
the INSERT ... VALUES statement only if multiple value lists are
specified in the statement.
A character string representing additional information about the most
recently executed query. NULL if no information is available for
the query.
None.
mysql_init()MYSQL *mysql_init(MYSQL *mysql)
Allocates or initialises a MYSQL object suitable for
mysql_real_connect(). If mysql is a NULL
pointer, the function allocates, initialises, and returns a new object.
Otherwise the object is initialised and the address of the object is returned.
If mysql_init() allocates a new object, it will be freed when
mysql_close() is called to close the connection.
An initialised MYSQL* handle. NULL if there was
insufficient memory to allocate a new object.
In case of insufficient memory, NULL is returned.
mysql_insert_id()my_ulonglong mysql_insert_id(MYSQL *mysql)
Returns the ID generated for an AUTO_INCREMENT column by the
previous query. Use this function after you have performed an
INSERT query into a table that contains an
AUTO_INCREMENT field.
Note that mysql_insert_id() returns 0 if the
previous query does not generate an AUTO_INCREMENT value. If you
need to save the value for later, be sure to call mysql_insert_id()
immediately after the query that generates the value.
mysql_insert_id() is updated after INSERT and
UPDATE statements that generate an AUTO_INCREMENT
value or that set a column value to LAST_INSERT_ID(expr). See
section 6.3.5.2
Miscellaneous Functions.
Also note that the value of the SQL LAST_INSERT_ID() function
always contains the most recently generated AUTO_INCREMENT value,
and is not reset between queries because the value of that function is
maintained in the server.
The value of the AUTO_INCREMENT field that was updated by the
previous query. Returns zero if there was no previous query on the connection or
if the query did not update an AUTO_INCREMENT value.
None.
mysql_kill()int mysql_kill(MYSQL *mysql, unsigned long pid)
Asks the server to kill the thread specified by pid.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_dbs()MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)
Returns a result set consisting of database names on the server that match
the simple regular expression specified by the wild parameter.
wild may contain the wild-card characters `%' or
`_', or may be a NULL pointer to match all databases.
Calling mysql_list_dbs() is similar to executing the query
SHOW databases [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_fields()MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const
char *wild)
Returns a result set consisting of field names in the given table that match
the simple regular expression specified by the wild parameter.
wild may contain the wild-card characters `%' or
`_', or may be a NULL pointer to match all fields.
Calling mysql_list_fields() is similar to executing the query
SHOW COLUMNS FROM tbl_name [LIKE wild].
Note that it's recommended that you use SHOW COLUMNS FROM
tbl_name instead of mysql_list_fields().
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_processes()MYSQL_RES *mysql_list_processes(MYSQL *mysql)
Returns a result set describing the current server threads. This is the same
kind of information as that reported by mysqladmin processlist or a
SHOW PROCESSLIST query.
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_tables()MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)
Returns a result set consisting of table names in the current database that
match the simple regular expression specified by the wild
parameter. wild may contain the wild-card characters
`%' or `_', or may be a NULL pointer to
match all tables. Calling mysql_list_tables() is similar to
executing the query SHOW tables [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_num_fields()unsigned int mysql_num_fields(MYSQL_RES *result)
or
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a
MYSQL* argument, you must use unsigned int
mysql_field_count(MYSQL *mysql) instead.
Returns the number of columns in a result set.
Note that you can get the number of columns either from a pointer to a result
set or to a connection handle. You would use the connection handle if
mysql_store_result() or mysql_use_result() returned
NULL (and thus you have no result set pointer). In this case, you
can call mysql_field_count() to determine whether or not
mysql_store_result() should have produced a non-empty result. This
allows the client program to take proper action without knowing whether or not
the query was a SELECT (or SELECT-like) statement. The
example shown below illustrates how this may be done.
See section 8.4.6.1
Why Is It that After mysql_query() Returns Success,
mysql_store_result() Sometimes Returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if (mysql_errno(&mysql))
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
else if (mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
}
}
An alternative (if you know that your query should have returned a result
set) is to replace the mysql_errno(&mysql) call with a check if
mysql_field_count(&mysql) is = 0. This will only happen if
something went wrong.
mysql_num_rows()my_ulonglong mysql_num_rows(MYSQL_RES *result)
Returns the number of rows in the result set.
The use of mysql_num_rows() depends on whether you use
mysql_store_result() or mysql_use_result() to return
the result set. If you use mysql_store_result(),
mysql_num_rows() may be called immediately. If you use
mysql_use_result(), mysql_num_rows() will not return
the correct value until all the rows in the result set have been retrieved.
The number of rows in the result set.
None.
mysql_options()int mysql_options(MYSQL *mysql, enum mysql_option option, const char
*arg)
Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.
mysql_options() should be called after mysql_init()
and before mysql_connect() or mysql_real_connect().
The option argument is the option that you want to set; the
arg argument is the value for the option. If the option is an
integer, then arg should point to the value of the integer.
Possible options values:
| Option | Argument type | Function |
MYSQL_OPT_CONNECT_TIMEOUT |
unsigned int * |
Connect timeout in seconds. |
MYSQL_OPT_COMPRESS |
Not used | Use the compressed client/server protocol. |
MYSQL_OPT_NAMED_PIPE |
Not used | Use named pipes to connect to a MySQL server on NT. |
MYSQL_INIT_COMMAND |
char * |
Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting. |
MYSQL_READ_DEFAULT_FILE |
char * |
Read options from the named option file instead of from `my.cnf'. |
MYSQL_READ_DEFAULT_GROUP |
char * |
Read options from the named group from `my.cnf' or the file
specified with MYSQL_READ_DEFAULT_FILE. |
Note that the group client is always read if you use
MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.
The specified group in the option file may contain the following options:
| Option | Description |
connect_timeout |
Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server. |
compress |
Use the compressed client/server protocol. |
database |
Connect to this database if no database was specified in the connect command. |
debug |
Debug options. |
host |
Default host name. |
init-command |
Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting. |
interactive-timeout |
Same as specifying CLIENT_INTERACTIVE to
mysql_real_connect(). See section 8.4.3.171
mysql_real_connect(). |
password |
Default password. |
pipe |
Use named pipes to connect to a MySQL server on NT. |
port |
Default port number. |
return-found-rows |
Tell mysql_info() to return found rows instead of updated
rows when using UPDATE. |
socket |
Default socket number. |
user |
Default user. |
Note that timeout has been replaced by
connect_timeout, but timeout will still work for a
while.
For more information about option files, see section 4.1.2 my.cnf Option Files.
Zero for success. Non-zero if you used an unknown option.
MYSQL mysql;
mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
The above requests the client to use the compressed client/server protocol
and read the additional options from the odbc section in the
my.cnf file.
mysql_ping()int mysql_ping(MYSQL *mysql)
Checks whether or not the connection to the server is working. If it has gone down, an automatic reconnection is attempted.
This function can be used by clients that remain idle for a long while, to check whether or not the server has closed the connection and reconnect if necessary.
Zero if the server is alive. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_UNKNOWN_ERROR
mysql_query()int mysql_query(MYSQL *mysql, const char *query)
Executes the SQL query pointed to by the null-terminated string
query. The query must consist of a single SQL statement. You should
not add a terminating semicolon (`;') or \g to the
statement.
mysql_query() cannot be used for queries that contain binary
data; you should use mysql_real_query() instead. (Binary data may
contain the `\0' character, which mysql_query()
interprets as the end of the query string.)
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this. See section 8.4.3.85
mysql_field_count().
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_real_connect()MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char
*user, const char *passwd, const char *db, unsigned int port, const char
*unix_socket, unsigned int client_flag)
mysql_real_connect() attempts to establish a connection to a
MySQL database engine running on host.
mysql_real_connect() must complete successfully before you can
execute any of the other API functions, with the exception of
mysql_get_client_info().
The parameters are specified as follows:
MYSQL structure. Before calling mysql_real_connect()
you must call mysql_init() to initialise the MYSQL
structure. You can change a lot of connect options with the
mysql_options() call. See section 8.4.3.159
mysql_options().
host may be either a hostname or an IP address.
If host is NULL or the string
"localhost", a connection to the local host is assumed. If the OS
supports sockets (Unix) or named pipes (Windows), they are used instead of
TCP/IP to connect to the server.
user parameter contains the user's MySQL login ID. If
user is NULL, the current user is assumed. Under
Unix, this is the current login name. Under Windows ODBC, the current user
name must be specified explicitly. See section 8.3.2
How to Fill in the Various Fields in the ODBC Administrator Program.
passwd parameter contains the password for
user. If passwd is NULL, only entries
in the user table for the user that have a blank (empty) password
field will be checked for a match. This allows the database administrator to
set up the MySQL privilege system in such a way that users get different
privileges depending on whether or not they have specified a password. NOTE:
Do not attempt to encrypt the password before calling
mysql_real_connect(); password encryption is handled
automatically by the client API.
db is the database name. If db is not
NULL, the connection will set the default database to this value.
port is not 0, the value will be used as the port number
for the TCP/IP connection. Note that the host parameter
determines the type of the connection.
unix_socket is not NULL, the string specifies
the socket or named pipe that should be used. Note that the host
parameter determines the type of the connection.
client_flag is usually 0, but can be set to a
combination of the following flags in very special circumstances:
| Flag name | Flag description |
CLIENT_COMPRESS |
Use compression protocol. |
CLIENT_FOUND_ROWS |
Return the number of found (matched) rows, not the number of affected rows. |
CLIENT_IGNORE_SPACE |
Allow spaces after function names. Makes all functions names reserved words. |
CLIENT_INTERACTIVE |
Allow interactive_timeout seconds (instead of
wait_timeout seconds) of inactivity before closing the
connection. |
CLIENT_NO_SCHEMA |
Don't allow the db_name.tbl_name.col_name syntax. This
is for ODBC. It causes the parser to generate an error if you use that
syntax, which is useful for trapping bugs in some ODBC programs. |
CLIENT_ODBC |
The client is an ODBC client. This changes mysqld to be
more ODBC-friendly. |
CLIENT_SSL |
Use SSL (encrypted protocol). |
A MYSQL* connection handle if the connection was successful,
NULL if the connection was unsuccessful. For a successful
connection, the return value is the same as the value of the first parameter.
CR_CONN_HOST_ERROR
CR_CONNECTION_ERROR
CR_IPSOCK_ERROR
CR_OUT_OF_MEMORY
CR_SOCKET_CREATE_ERROR
CR_UNKNOWN_HOST
CR_VERSION_ERROR
--old-protocol option.
CR_NAMEDPIPEOPEN_ERROR
CR_NAMEDPIPEWAIT_ERROR
CR_NAMEDPIPESETSTATE_ERROR
CR_SERVER_LOST
connect_timeout > 0 and it took longer then
connect_timeout seconds to connect to the server or if the server
died while executing the init-command. MYSQL mysql;
mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
By using mysql_options() the MySQL library will read the
[client] and your_prog_name sections in the
my.cnf file which will ensure that your program will work, even if
someone has set up MySQL in some non-standard way.
Note that upon connection, mysql_real_connect() sets the
reconnect flag (part of the MYSQL structure) to a value of
1. This flag indicates, in the event that a query cannot be
performed because of a lost connection, to try reconnecting to the server before
giving up.
mysql_real_escape_string()unsigned int mysql_real_escape_string(MYSQL *mysql, char *to, const
char *from, unsigned int length)
This function is used to create a legal SQL string that you can use in a SQL statement. See section 6.1.1.1 Strings.
The string in from is encoded to an escaped SQL string, taking
into account the current character set of the connection. The result is placed
in to and a terminating null byte is appended. Characters encoded
are NUL (ASCII 0), `\n', `\r',
`\', `'', `"', and Control-Z (see section
6.1.1
Literals: How to Write Strings and Numbers).
The string pointed to by from must be length bytes
long. You must allocate the to buffer to be at least
length*2+1 bytes long. (In the worse case, each character may need
to be encoded as using two bytes, and you need room for the terminating null
byte.) When mysql_escape_string() returns, the contents of
to will be a null-terminated string. The return value is the length
of the encoded string, not including the terminating null character.
char query[1000],*end;
end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';
if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
fprintf(stderr, "Failed to insert row, Error: %s\n",
mysql_error(&mysql));
}
The strmov() function used in the example is included in the
mysqlclient library and works like strcpy() but
returns a pointer to the terminating null of the first parameter.
The length of the value placed into to, not including the
terminating null character.
None.
mysql_real_query()int mysql_real_query(MYSQL *mysql, const char *query, unsigned int
length)
Executes the SQL query pointed to by query, which should be a
string length bytes long. The query must consist of a single SQL
statement. You should not add a terminating semicolon (`;') or
\g to the statement.
You must use mysql_real_query() rather than
mysql_query() for queries that contain binary data, because binary
data may contain the `\0' character. In addition,
mysql_real_query() is faster than mysql_query()
because it does not call strlen() on the query string.
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this. See section 8.4.3.85
mysql_field_count().
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_reload()int mysql_reload(MYSQL *mysql)
Asks the MySQL server to reload the grant tables. The connected user must have the reload privilege.
This function is deprecated. It is preferable to use
mysql_query() to issue a SQL FLUSH PRIVILEGES
statement instead.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_row_seek()MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET
offset)
Sets the row cursor to an arbitrary row in a query result set. This requires
that the result set structure contains the entire result of the query, so
mysql_row_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value returned from a call to
mysql_row_tell() or to mysql_row_seek(). This value is
not simply a row number; if you want to seek to a row within a result set using
a row number, use mysql_data_seek() instead.
The previous value of the row cursor. This value may be passed to a
subsequent call to mysql_row_seek().
None.
mysql_row_tell()MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)
Returns the current position of the row cursor for the last
mysql_fetch_row(). This value can be used as an argument to
mysql_row_seek().
You should use mysql_row_tell() only after
mysql_store_result(), not after mysql_use_result().
The current offset of the row cursor.
None.
mysql_select_db()int mysql_select_db(MYSQL *mysql, const char *db)
Causes the database specified by db to become the default
(current) database on the connection specified by mysql. In
subsequent queries, this database is the default for table references that do
not include an explicit database specifier.
mysql_select_db() fails unless the connected user can be
authenticated as having permission to use the database.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_shutdown()int mysql_shutdown(MYSQL *mysql)
Asks the database server to shut down. The connected user must have shutdown privileges.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_stat()char *mysql_stat(MYSQL *mysql)
Returns a character string containing information similar to that provided by
the mysqladmin status command. This includes uptime in seconds and
the number of running threads, questions, reloads, and open tables.
A character string describing the server status. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_store_result()MYSQL_RES *mysql_store_result(MYSQL *mysql)
You must call mysql_store_result() or
mysql_use_result() for every query that successfully retrieves data
(SELECT, SHOW, DESCRIBE,
EXPLAIN).
You don't have to call mysql_store_result() or
mysql_use_result() for other queries, but it will not do any harm
or cause any notable performance if you call mysql_store_result()
in all cases. You can detect if the query didn't have a result set by checking
if mysql_store_result() returns 0 (more about this later one).
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this. See section 8.4.3.85
mysql_field_count().
mysql_store_result() reads the entire result of a query to the
client, allocates a MYSQL_RES structure, and places the result into
this structure.
mysql_store_result() returns a null pointer if the query didn't
return a result set (if the query was, for example, an INSERT
statement).
mysql_store_result() also returns a null pointer if reading of
the result set failed. You can check if you got an error by checking if
mysql_error() doesn't return a null pointer, if
mysql_errno() returns <> 0, or if
mysql_field_count() returns <> 0.
An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)
Once you have called mysql_store_result() and got a result back
that isn't a null pointer, you may call mysql_num_rows() to find
out how many rows are in the result set.
You can call mysql_fetch_row() to fetch rows from the result
set, or mysql_row_seek() and mysql_row_tell() to
obtain or set the current row position within the result set.
You must call mysql_free_result() once you are done with the
result set.
See section 8.4.6.1
Why Is It that After mysql_query() Returns Success,
mysql_store_result() Sometimes Returns NULL?.
A MYSQL_RES result structure with the results. NULL
if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_thread_id()unsigned long mysql_thread_id(MYSQL *mysql)
Returns the thread ID of the current connection. This value can be used as an
argument to mysql_kill() to kill the thread.
If the connection is lost and you reconnect with mysql_ping(),
the thread ID will change. This means you should not get the thread ID and store
it for later. You should get it when you need it.
The thread ID of the current connection.
None.
mysql_use_result()MYSQL_RES *mysql_use_result(MYSQL *mysql)
You must call mysql_store_result() or
mysql_use_result() for every query that successfully retrieves data
(SELECT, SHOW, DESCRIBE,
EXPLAIN).
mysql_use_result() initiates a result set retrieval but does not
actually read the result set into the client like
mysql_store_result() does. Instead, each row must be retrieved
individually by making calls to mysql_fetch_row(). This reads the
result of a query directly from the server without storing it in a temporary
table or local buffer, which is somewhat faster and uses much less memory than
mysql_store_result(). The client will only allocate memory for the
current row and a communication buffer that may grow up to
max_allowed_packet bytes.
On the other hand, you shouldn't use mysql_use_result() if you
are doing a lot of processing for each row on the client side, or if the output
is sent to a screen on which the user may type a ^S (stop scroll).
This will tie up the server and prevent other threads from updating any tables
from which the data is being fetched.
When using mysql_use_result(), you must execute
mysql_fetch_row() until a NULL value is returned,
otherwise the unfetched rows will be returned as part of the result set for your
next query. The C API will give the error Commands out of sync; You can't
run this command now if you forget to do this!
You may not use mysql_data_seek(),
mysql_row_seek(), mysql_row_tell(),
mysql_num_rows(), or mysql_affected_rows() with a
result returned from mysql_use_result(), nor may you issue other
queries until the mysql_use_result() has finished. (However, after
you have fetched all the rows, mysql_num_rows() will accurately
return the number of rows fetched.)
You must call mysql_free_result() once you are done with the
result set.
A MYSQL_RES result structure. NULL if an error
occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
You need to use the following functions when you want to create a threaded client. See section 8.4.8 How to Make a Threaded Client.
my_init()This function needs to be called once in the program before calling any MySQL
function. This initialises some global variables that MySQL needs. If you are
using a thread-safe client library, this will also call
mysql_thread_init() for this thread.
This is automatically called by mysql_init(),
mysql_server_init() and mysql_connect().
none.
mysql_thread_init()This function needs to be called for each created thread to initialise thread specific variables.
This is automatically called by my_init() and
mysql_connect().
none.
mysql_thread_end()This function needs to be called before calling pthread_exit()
to free memory allocated by mysql_thread_init().
Note that this function is not invoked automatically by the client library. It must be called explicitly to avoid a memory leak.
none.
You must use the following functions if you want to allow your application to be linked against the embedded MySQL server library. See section 8.4.9 libmysqld, the Embedded MySQL Server Library.
If the program is linked with -lmysqlclient instead of
-lmysqld, these functions do nothing. This makes it possible to
choose between using the embedded MySQL server and a stand-alone server without
modifying any code.
mysql_server_init()int mysql_server_init(int argc, char **argv, char **groups)
This function must be called once in the program before
calling any other MySQL function. It starts up the server and initialises any
subsystems (mysys, InnoDB, etc.) that the server uses. If this
function is not called, the program will crash. If you are using the DBUG
package that comes with MySQL, you should call this after you have called
MY_INIT().
The argc and argv arguments are analogous to the
arguments to main(). The first element of argv is
ignored (it typically contains the program name). For convenience,
argc may be 0 (zero) if there are no command-line
arguments for the server.
The NULL-terminated list of strings in groups
selects which groups in the option files will be active. See section 4.1.2
my.cnf Option Files. For convenience, groups may be
NULL, in which case the [server] and
[emedded] groups will be active.
#include <mysql.h>
#include <stdlib.h>
static char *server_args[] = {
"this_program", /* this string is not used */
"--datadir=.",
"--set-variable=key_buffer_size=32M"
};
static char *server_groups[] = {
"embedded",
"server",
"this_program_SERVER",
(char *)NULL
};
int main(void) {
mysql_server_init(sizeof(server_args) / sizeof(char *),
server_args, server_groups);
/* Use any MySQL API functions here */
mysql_server_end();
return EXIT_SUCCESS;
}
0 if okay, 1 if an error occurred.
mysql_server_end()This function must be called once in the program after all other MySQL functions. It shuts down the embedded server.
none.
mysql_query() Returns Success, mysql_store_result()
Sometimes Returns NULL?It is possible for mysql_store_result() to return
NULL following a successful call to mysql_query().
When this happens, it means one of the following conditions occurred:
malloc() failure (for example, if the result set
was too large).
INSERT,
UPDATE, or DELETE). You can always check whether or not the statement should have produced a
non-empty result by calling mysql_field_count(). If
mysql_field_count() returns zero, the result is empty and the last
query was a statement that does not return values (for example, an
INSERT or a DELETE). If
mysql_field_count() returns a non-zero value, the statement should
have produced a non-empty result. See the description of the
mysql_field_count() function for an example.
You can test for an error by calling mysql_error() or
mysql_errno().
In addition to the result set returned by a query, you can also get the following information:
mysql_affected_rows() returns the number of rows affected by
the last query when doing an INSERT, UPDATE, or
DELETE. An exception is that if DELETE is used
without a WHERE clause, the table is re-created empty, which is
much faster! In this case, mysql_affected_rows() returns zero for
the number of records affected.
mysql_num_rows() returns the number of rows in a result set.
With mysql_store_result(), mysql_num_rows() may be
called as soon as mysql_store_result() returns. With
mysql_use_result(), mysql_num_rows() may be called
only after you have fetched all the rows with mysql_fetch_row().
mysql_insert_id() returns the ID generated by the last query
that inserted a row into a table with an AUTO_INCREMENT index.
See section 8.4.3.126
mysql_insert_id().
LOAD DATA INFILE ..., INSERT INTO ...
SELECT ..., UPDATE) return additional information. The
result is returned by mysql_info(). See the description for
mysql_info() for the format of the string that it returns.
mysql_info() returns a NULL pointer if there is no
additional information. If you insert a record in a table containing a column that has the
AUTO_INCREMENT attribute, you can get the most recently generated
ID by calling the mysql_insert_id() function.
You can also retrieve the ID by using the LAST_INSERT_ID()
function in a query string that you pass to mysql_query().
You can check if an AUTO_INCREMENT index is used by executing
the following code. This also checks if the query was an INSERT
with an AUTO_INCREMENT index:
if (mysql_error(&mysql)[0] == 0 &&
mysql_num_fields(result) == 0 &&
mysql_insert_id(&mysql) != 0)
{
used_id = mysql_insert_id(&mysql);
}
The most recently generated ID is maintained in the server on a
per-connection basis. It will not be changed by another client. It will not even
be changed if you update another AUTO_INCREMENT column with a
non-magic value (that is, a value that is not NULL and not
0).
If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:
INSERT INTO foo (auto,text)
VALUES(NULL,'text'); # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
VALUES(LAST_INSERT_ID(),'text'); # use ID in second table
When linking with the C API, the following errors may occur on some systems:
gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors. No output written to client
If this happens on your system, you must include the math library by adding
-lm to the end of the compile/link line.
If you compile MySQL clients that you've written yourself or that you obtain
from a third party, they must be linked using the -lmysqlclient -lz
option on the link command. You may also need to specify a -L
option to tell the linker where to find the library. For example, if the library
is installed in `/usr/local/mysql/lib', use
-L/usr/local/mysql/lib -lmysqlclient -lz on the link command.
For clients that use MySQL header files, you may need to specify a
-I option when you compile them (for example,
-I/usr/local/mysql/include), so the compiler can find the header
files.
The client library is almost thread safe. The biggest problem is that the
subroutines in `net.c' that read from sockets are not interrupt safe.
This was done with the thought that you might want to have your own alarm that
can break a long read to a server. If you install interrupt handlers for the
SIGPIPE interrupt, the socket handling should be thread safe.
In the older binaries we distribute on our web site (http://mysql.com/), the client libraries are not normally compiled with the thread-safe option (the Windows binaries are by default compiled to be thread safe). Newer binary distributions should have both a normal and a thread-safe client library.
To get a threaded client where you can interrupt the client from other
threads and set timeouts when talking with the MySQL server, you should use the
-lmysys, -lstring, and -ldbug libraries
and the net_serv.o code that the server uses.
If you don't need interrupts or timeouts, you can just compile a thread safe
client library (mysqlclient_r) and use this. See section 8.4 MySQL C
API. In this case you don't have to worry about the net_serv.o
object file or the other MySQL libraries.
When using a threaded client and you want to use timeouts and interrupts, you
can make great use of the routines in the `thr_alarm.c' file. If you
are using routines from the mysys library, the only thing you must
remember is to call my_init() first! See section 8.4.4
C Threaded Function Descriptions.
All functions except mysql_real_connect() are by default thread
safe. The following notes describe how to compile a thread-safe client library
and use it in a thread-safe manner. (The notes below for
mysql_real_connect() actually apply to mysql_connect()
as well, but because mysql_connect() is deprecated, you should be
using mysql_real_connect() anyway.)
To make mysql_real_connect() thread safe, you must recompile the
client library with this command:
shell> ./configure --enable-thread-safe-client
This will create a thread-safe client library libmysqlclient_r.
--enable-thread-safe-client. This library is thread safe per
connection. You can let two threads share the same connection with the following
caveats:
mysql_query() and mysql_store_result() no other
thread is using the same connection.
mysql_store_result().
mysql_use_result, you have to ensure that no other
thread is using the same connection until the result set is closed. However,
it really is best for threaded clients that share the same connection to use
mysql_store_result().
mysql_query() and
mysql_store_result() call combination. Once
mysql_store_result() is ready, the lock can be released and other
threads may query the same connection.
pthread_mutex_lock() and pthread_mutex_unlock() to
establish and release a mutex lock. You need to know the following if you have a thread that is calling MySQL functions which did not create the connection to the MySQL database:
When you call mysql_init() or mysql_connect(),
MySQL will create a thread specific variable for the thread that is used by the
debug library (among other things).
If you call a MySQL function, before the thread has called
mysql_init() or mysql_connect(), the thread will not
have the necessary thread specific variables in place and you are likely to end
up with a core dump sooner or later. The get things to work smoothly you have to
do the following:
my_init() at the start of your program if it calls any
other MySQL function before calling mysql_real_connect().
mysql_thread_init() in the thread handler before calling
any MySQL function.
mysql_thread_end() before calling
pthread_exit(). This will free the memory used by MySQL thread
specific variables. You may get some errors because of undefined symbols when linking your client
with libmysqlclient_r. In most cases this is because you haven't
included the thread libraries on the link/compile line.
The embedded MySQL server library makes it possible to run a full-featured MySQL server inside the client application. The main benefits are increased speed and more simple management for embedded applications.
The API is identical for the embedded MySQL version and the client/server version. To change an old threaded application to use the embedded library, you normally only have to add calls to the following functions:
| Function | When to call |
mysql_server_init() |
Should be called before any other other MySQL function is called,
preferably early in the main() function. |
mysql_server_end() |
Should be called before your program exits. |
mysql_thread_init() |
Should be called in each thread you create that will access MySQL. |
mysql_thread_end() |
Should be called before calling pthread_exit()
|
Then you must link your code with libmysqld.a instead of
libmysqlclient.a.
The above mysql_server_xxx functions are also included in
libmysqlclient.a to allow you to change between the embedded and
the client/server version by just linking your application with the right
library. See section 8.4.5.1
mysql_server_init().
libmysqldTo get a libmysqld library you should configure MySQL with the
--with-embedded-server option.
When you link your program with libmysqld, you must also include
the system-specific pthread libraries and some libraries that the
MySQL server uses. You can get the full list of libraries by executing
mysql_config --libmysqld-libs. The correct flags for compiling and
linking a threaded program must be used, even if you do not directly call any
thread functions in your code.
The embedded server has the following limitations:
Some of these limitations can be changed by editing the `mysql_embed.h' include file and recompiling MySQL.
The following is the recommended way to use option files to make it easy to switch between a client/server application and one where MySQL is embedded. See section 4.1.2 my.cnf Option Files.
[server] section. These will be
read by both MySQL versions.
[mysqld] section.
[embedded]
section.
[ApplicationName_SERVER] section. mysqld
library, in the future we will also provide a shared library for this.
This example program and makefile should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes will be needed. This example is designed to give enough details to understand the problem, without the clutter that is a necessary part of a real application.
To try out the example, create an `test_libmysqld' directory at the same level as the mysql-4.0 source directory. Save the `test_libmysqld.c' source and the `GNUmakefile' in the directory, and run GNU `make' from inside the `test_libmysqld' directory.
`test_libmysqld.c'
/*
* A simple example client, using the embedded MySQL server library
*/
#include <mysql.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
MYSQL *db_connect(const char *dbname);
void db_disconnect(MYSQL *db);
void db_do_query(MYSQL *db, const char *query);
const char *server_groups[] = {
"test_libmysqld_SERVER", "embedded", "server", NULL
};
int
main(int argc, char **argv)
{
MYSQL *one, *two;
/* mysql_server_init() must be called before any other mysql
* functions.
*
* You can use mysql_server_init(0, NULL, NULL), and it will
* initialise the server using groups = {
* "server", "embedded", NULL
* }.
*
* In your $HOME/.my.cnf file, you probably want to put:
[test_libmysqld_SERVER]
language = /path/to/source/of/mysql/sql/share/english
* You could, of course, modify argc and argv before passing
* them to this function. Or you could create new ones in any
* way you like. But all of the arguments in argv (except for
* argv[0], which is the program name) should be valid options
* for the MySQL server.
*
* If you link this client against the normal mysqlclient
* library, this function is just a stub that does nothing.
*/
mysql_server_init(argc, argv, (char **)server_groups);
one = db_connect("test");
two = db_connect(NULL);
db_do_query(one, "show table status");
db_do_query(two, "show databases");
mysql_close(two);
mysql_close(one);
/* This must be called after all other mysql functions */
mysql_server_end();
exit(EXIT_SUCCESS);
}
static void
die(MYSQL *db, char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
(void)putc('\n', stderr);
if (db)
db_disconnect(db);
exit(EXIT_FAILURE);
}
MYSQL *
db_connect(const char *dbname)
{
MYSQL *db = mysql_init(NULL);
if (!db)
die(db, "mysql_init failed: no memory");
/*
* Notice that the client and server use separate group names.
* This is critical, because the server will not accept the
* client's options, and vice versa.
*/
mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test_libmysqld_CLIENT");
if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0))
die(db, "mysql_real_connect failed: %s", mysql_error(db));
return db;
}
void
db_disconnect(MYSQL *db)
{
mysql_close(db);
}
void
db_do_query(MYSQL *db, const char *query)
{
if (mysql_query(db, query) != 0)
goto err;
if (mysql_field_count(db) > 0)
{
MYSQL_RES *res;
MYSQL_ROW row, end_row;
int num_fields;
if (!(res = mysql_store_result(db)))
goto err;
num_fields = mysql_num_fields(res);
while ((row = mysql_fetch_row(res)))
{
(void)fputs(">> ", stdout);
for (end_row = row + num_fields; row < end_row; ++row)
(void)printf("%s\t", row ? (char*)*row : "NULL");
(void)fputc('\n', stdout);
}
(void)fputc('\n', stdout);
}
else
(void)printf("Affected rows: %lld\n", mysql_affected_rows(db));
return;
err:
die(db, "db_do_query failed: %s [%s]", mysql_error(db), query);
}
`GNUmakefile'
# This assumes the MySQL software is installed in /usr/local/mysql inc := /usr/local/mysql/include/mysql lib := /usr/local/mysql/lib # If you have not installed the MySQL software yet, try this instead #inc := $(HOME)/mysql-4.0/include #lib := $(HOME)/mysql-4.0/libmysqld CC := gcc CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT CFLAGS := -g -W -Wall LDFLAGS := -static # You can change -lmysqld to -lmysqlclient to use the # client/server library LDLIBS = -L$(lib) -lmysqld -lz -lm -lcrypt ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null)) # FreeBSD LDFLAGS += -pthread else # Assume Linux LDLIBS += -lpthread endif # This works for simple one-file test programs sources := $(wildcard *.c) objects := $(patsubst %c,%o,$(sources)) targets := $(basename $(sources)) all: $(targets) clean: rm -f $(targets) $(objects) *.core
The MySQL source code is covered by the GNU GPL license (see section H GNU
GENERAL PUBLIC LICENSE). One result of this is that any program which
includes, by linking with libmysqld, the MySQL source code must be
released as free software (under a license compatible with the GPL).
We encourage everyone to promote free software by releasing code under the GPL or a compatible license. For those who are not able to do this, another option is to purchase the MySQL code from MySQL AB under a looser license. For details concerning this issue, please see section 1.4.3 MySQL Server Licenses.
Two APIs are available in the MySQL Contrib directory (http://mysql.com/Downloads/Contrib/).
You can compile the MySQL Windows source with Borland C++ 5.02. (The Windows source includes only projects for Microsoft VC++, for Borland C++ you have to do the project files yourself.)
One known problem with Borland C++ is that it uses a different structure
alignment than VC++. This means that you will run into problems if you try to
use the default libmysql.dll libraries (that was compiled with
VC++) with Borland C++. You can do one of the following to avoid this problem.
mysql_init() with NULL as an argument,
not a pre-allocated MYSQL struct. There are 2 supported JDBC drivers for MySQL (the mm driver and the Reisin JDBC driver). You can find a copy of the mm driver at http://mmmysql.sourceforge.net/ or http://mysql.com/Downloads/Contrib/ and the Reisin driver at http://www.caucho.com/projects/jdbc-mysql/index.xtp For documentation consult any JDBC documentation and the driver's own documentation for MySQL-specific features.
The MySQL Contrib directory (http://mysql.com/Downloads/Contrib/) contains a Python interface written by Joseph Skinner.
You can also use the Python interface to iODBC to access a MySQL server. http://starship.skyport.net/~lemburg/ (mxODBC)
http://www.binevolve.com/~tdarugar/tcl-sql/ (Tcl at binevolve). The Contrib directory (http://mysql.com/Downloads/Contrib/) contains a Tcl interface that is based on msqltcl 1.50.
The MySQL Contrib directory (http://mysql.com/Downloads/Contrib/) contains an Eiffel wrapper written by Michael Ravits.
This chapter describes a lot of things that you need to know when working on
the MySQL code. If you plan to contribute to MySQL development, want to have
access to the bleeding-edge in-between versions code, or just want to keep track
of development, follow the instructions in See section 2.3.4
Installing from the Development Source Tree. If you are interested in MySQL
internals, you should also subscribe to our internals mailing list.
This list is relatively low traffic. For details on how to subscribe, please see
section 1.6.2.1
The MySQL Mailing Lists. All developers at MySQL AB are on the
internals list and we help other people who are working on the
MySQL code. Feel free to use this list both to ask questions about the code and
to send patches that you would like to contribute to the MySQL project!
The MySQL server creates the following threads:
process_alarm() to force timeouts on connections
that have been idle too long.
mysqld is compiled with -DUSE_ALARM_THREAD, a
dedicated thread that handles alarms is created. This is only used on some
systems where there are problems with sigwait() or if one wants
to use the thr_alarm() code in ones application without a
dedicated signal handling thread.
--flush_time=# option, a dedicated thread is
created to flush all tables at the given interval.
INSERT DELAYED gets
its own thread.
--master-host, a slave replication thread will be
started to read and apply updates from the master. mysqladmin processlist only shows the connection, INSERT
DELAYED, and replication threads.
Until recently, our main full-coverage test suite was based on proprietary
customer data and for that reason has not been publicly available. The only
publicly available part of our testing process consisted of the
crash-me test, a Perl DBI/DBD benchmark found in the
sql-bench directory, and miscellaneous tests located in
tests directory. The lack of a standardised publicly available test
suite has made it difficult for our users, as well developers, to do regression
tests on the MySQL code. To address this problem, we have created a new test
system that is included in the source and binary distributions starting in
Version 3.23.29.
The current set of test cases doesn't test everything in MySQL, but it should catch most obvious bugs in the SQL processing code, OS/library issues, and is quite thorough in testing replication. Our eventual goal is to have the tests cover 100% of the code. We welcome contributions to our test suite. You may especially want to contribute tests that examine the functionality critical to your system, as this will ensure that all future MySQL releases will work well with your applications.
The test system consist of a test language interpreter
(mysqltest), a shell script to run all
tests(mysql-test-run), the actual test cases written in a special
test language, and their expected results. To run the test suite on your system
after a build, type make test or
mysql-test/mysql-test-run from the source root. If you have
installed a binary distribution, cd to the install root (eg.
/usr/local/mysql), and do scripts/mysql-test-run. All
tests should succeed. If not, you should try to find out why and report the
problem if this is a bug in MySQL. See section 9.1.2.3
Reporting Bugs in the MySQL Test Suite.
If you have a copy of mysqld running on the machine where you
want to run the test suite you do not have to stop it, as long as it is not
using ports 9306 and 9307. If one of those ports is
taken, you should edit mysql-test-run and change the values of the
master and/or slave port to one that is available.
You can run one individual test case with mysql-test/mysql-test-run
test_name.
If one test fails, you should test running mysql-test-run with
the --force option to check if any other tests fails.
You can use the mysqltest language to write your own test cases.
Unfortunately, we have not yet written full documentation for it - we plan to do
this shortly. You can, however, look at our current test cases and use them as
an example. The following points should help you get started:
mysql-test/t/*.test
; terminated statements and is
similar to the input of mysql command line client. A statement by
default is a query to be sent to MySQL server, unless it is recognised as
internal command (eg. sleep).
SELECT,
SHOW, EXPLAIN, etc., must be preceded with
@/path/to/result/file. The file must contain the expected
results. An easy way to generate the result file is to run mysqltest -r
< t/test-case-name.test from mysql-test directory, and
then edit the generated result files, if needed, to adjust them to the
expected output. In that case, be very careful about not adding or deleting
any invisible characters - make sure to only change the text and/or delete
lines. If you have to insert a line, make sure the fields are separated with a
hard tab, and there is a hard tab at the end. You may want to use od
-c to make sure your text editor has not messed anything up during
edit. We, of course, hope that you will never have to edit the output of
mysqltest -r as you only have to do it when you find a bug.
mysql-test/r directory and name them
test_name.result. If the test produces more than one result, you
should use test_name.a.result, test_name.b.result,
etc.
--error error-number. The error number
can be a list of possible error numbers separated with ','.
source include/master-slave.inc;. To switch
between master and slave, use connection master; and
connection slave;. If you need to do something on an alternate
connection, you can do connection master1; for the master, and
connection slave1; for the slave.
let $1=1000;
while ($1)
{
# do your queries here
dec $1;
}
sleep command. It supports
fractions of a second, so you can do sleep 1.3;, for example, to
sleep 1.3 seconds.
mysql-test/t/test_name-slave.opt. For
the master, put them in mysql-test/t/test_name-master.opt.
If your MySQL version doesn't pass the test suite you should do the following:
mysqlbug script
so that we can get information about your system and MySQL
version. See section 1.6.2.3
How to Report Bugs or Problems.
mysql-test-run, as well as
contents of all .reject files in mysql-test/r
directory.
cd mysql-test mysql-test-run --local test-nameIf this fails, then you should configure MySQL with
--with-debug and run mysql-test-run with the
--debug option. If this also fails send the trace file
`var/tmp/master.trace' to ftp://support.mysql.com/pub/mysql/secret so
that we can examine it. Please remember to also include a full description of
your system, the version of the mysqld binary and how you compiled it.
mysql-test-run with the --force
option to see if there is any other test that fails.
Result length mismatch or
Result content mismatch it means that the output of the test
didn't match exactly the expected output. This could be a bug in MySQL or that
your mysqld version produces slight different results under some
circumstances. Failed test results are put in a file with the same base name
as the result file with the .reject extension. If your test case
is failing, you should do a diff on the two files. If you cannot see how they
are different, examine both with od -c and also check their
lengths.
mysql-test/var/log directory for hints of what went wrong.
mysql-test-run with the --gdb and/or
--debug options. See section E.1.2
Creating trace files. If you have not compiled MySQL for debugging you
should probably do that. Just specify the --with-debug options to
configure! See section 2.3
Installing a MySQL Source Distribution. There are two ways to add new functions to MySQL:
CREATE FUNCTION and DROP FUNCTION statements.
See section 9.2.1
CREATE FUNCTION/DROP FUNCTION Syntax.
mysqld server and become
available on a permanent basis. Each method has advantages and disadvantages:
Whichever method you use to add new functions, they may be used just like
native functions such as ABS() or SOUNDEX().
CREATE FUNCTION/DROP FUNCTION
SyntaxCREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER}
SONAME shared_library_name
DROP FUNCTION function_name
A user-definable function (UDF) is a way to extend MySQL with a new function
that works like native (built in) MySQL functions such as ABS() and
CONCAT().
AGGREGATE is a new option for MySQL Version 3.23. An
AGGREGATE function works exactly like a native MySQL
GROUP function like SUM or COUNT().
CREATE FUNCTION saves the function's name, type, and shared
library name in the mysql.func system table. You must have the
insert and delete privileges for the
mysql database to create and drop functions.
All active functions are reloaded each time the server starts, unless you
start mysqld with the --skip-grant-tables option. In
this case, UDF initialisation is skipped and UDFs are unavailable. (An active
function is one that has been loaded with CREATE FUNCTION and not
removed with DROP FUNCTION.)
For instructions on writing user-definable functions, see section 9.2
Adding New Functions to MySQL. For the UDF mechanism to work, functions must
be written in C or C++, your operating system must support dynamic loading and
you must have compiled mysqld dynamically (not statically).
Note that to make AGGREGATE work, you must have a
mysql.func table that contains the column type. If
this is not the case, you should run the script
mysql_fix_privilege_tables to get this fixed.
For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. The MySQL source distribution includes a file `sql/udf_example.cc' that defines 5 new functions. Consult this file to see how UDF calling conventions work.
For mysqld to be able to use UDF functions, you should configure
MySQL with --with-mysqld-ldflags=-rdynamic The reason is that to on
many platforms (including Linux) you can load a dynamic library (with
dlopen()) from a static linked program, which you would get if you
are using --with-mysqld-ldflags=-all-static If you want to use an
UDF that needs to access symbols from mysqld (like the
methaphone example in `sql/udf_example.cc' that uses
default_charset_info), you must link the program with
-rdynamic (see man dlopen).
For each function that you want to use in SQL statements, you should define
corresponding C (or C++) functions. In the discussion below, the name ``xxx'' is
used for an example function name. To distinquish between SQL and C/C++ usage,
XXX() (uppercase) indicates a SQL function call, and
xxx() (lowercase) indicates a C/C++ function call.
The C/C++ functions that you write to implement the interface for
XXX() are:
xxx() (required)
| SQL type | C/C++ type |
STRING |
char * |
INTEGER |
long long |
REAL |
double |
xxx_init() (optional)
xxx(). It can be used to:
XXX().
REAL functions) the maximum number of
decimals.
NULL. xxx_deinit() (optional)
xxx(). It should deallocate
any memory allocated by the initialisation function. When a SQL statement invokes XXX(), MySQL calls the
initialisation function xxx_init() to let it perform any required
setup, such as argument checking or memory allocation. If
xxx_init() returns an error, the SQL statement is aborted with an
error message and the main and deinitialisation functions are not called.
Otherwise, the main function xxx() is called once for each row.
After all rows have been processed, the deinitialisation function
xxx_deinit() is called so it can perform any required cleanup.
For aggregate functions (like SUM()), you must also provide the
following functions:
xxx_reset() (required)
xxx_add() (required)
When using aggregate UDF functions MySQL works the following way:
xxx_init() to let the aggregate function allocate the
memory it will need to store results.
GROUP BY expression.
xxx_reset()
function.
xxx_add() function.
xxx() to get the result for the aggregate.
xxx_deinit() to let the UDF free any memory it has
allocated. All functions must be thread safe (not just the main function, but the
initialisation and deinitialisation functions as well). This means that you are
not allowed to allocate any global or static variables that change! If you need
memory, you should allocate it in xxx_init() and free it in
xxx_deinit().
The main function should be declared as shown below. Note that the return
type and parameters differ, depending on whether you will declare the SQL
function XXX() to return STRING, INTEGER,
or REAL in the CREATE FUNCTION statement:
For STRING functions:
char *xxx(UDF_INIT *initid, UDF_ARGS *args,
char *result, unsigned long *length,
char *is_null, char *error);
For INTEGER functions:
long long xxx(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
For REAL functions:
double xxx(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
The initialisation and deinitialisation functions are declared like this:
my_bool xxx_init(UDF_INIT *initid, UDF_ARGS *args, char *message); void xxx_deinit(UDF_INIT *initid);
The initid parameter is passed to all three functions. It points
to a UDF_INIT structure that is used to communicate information
between functions. The UDF_INIT structure members are listed below.
The initialisation function should fill in any members that it wishes to change.
(To use the default for a member, leave it unchanged.):
my_bool maybe_null
xxx_init() should set maybe_null to
1 if xxx() can return NULL. The default
value is 1 if any of the arguments are declared
maybe_null.
unsigned int decimals
1.34, 1.345, and 1.3, the
default would be 3, because 1.345 has 3 decimals.
unsigned int max_length
initid->decimals. (For numeric
functions, the length includes any sign or decimal point characters.) If you
want to return a blob, you can set this to 65K or 16M; This memory is not
allocated but used to decide which column type to use if there is a need to
temporary store the data.
char *ptr
initid->ptr to communicate allocated memory
between functions. In xxx_init(), allocate the memory and assign
it to this pointer: initid->ptr = allocated_memory;In
xxx() and xxx_deinit(), refer to
initid->ptr to use or deallocate the memory. Here follows a description of the different functions you need to define when you want to create an aggregate UDF function.
char *xxx_reset(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
This function is called when MySQL finds the first row in a new group. In the function you should reset any internal summary variables and then set the given argument as the first argument in the group.
In many cases this is implemented internally by reseting all variables and
then calling xxx_add().
char *xxx_add(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
This function is called for all rows that belongs to the same group, except for the first row. In this you should add the value in UDF_ARGS to your internal summary variable.
The xxx() function should be declared identical as when you
define a simple UDF function. See section 9.2.2.1
UDF Calling Sequences for simple functions.
This function is called when all rows in the group has been processed. You
should normally never access the args variable here but return your
value based on your internal summary variables.
All argument processing in xxx_reset() and
xxx_add() should be done identically as for normal UDF functions.
See section 9.2.2.3
Argument Processing.
The return value handling in xxx() should be done identically as
for a normal UDF. See section 9.2.2.4
Return Values and Error Handling.
The pointer argument to is_null and error is the
same for all calls to xxx_reset(), xxx_add() and
xxx(). You can use this to remember that you got an error or if the
xxx() function should return NULL. Note that you
should not store a string into *error! This is just a 1 byte flag!
is_null is reset for each group (before calling
xxx_reset(). error is never reset.
If isnull or error are set after xxx()
then MySQL will return NULL as the result for the group function.
The args parameter points to a UDF_ARGS structure
that has the members listed below:
unsigned int arg_count
if (args->arg_count != 2)
{
strcpy(message,"XXX() requires two arguments");
return 1;
}
enum Item_result *arg_type
STRING_RESULT, INT_RESULT, and
REAL_RESULT. To make sure that arguments are of a given type and
return an error if they are not, check the arg_type array in the
initialisation function. For example: if (args->arg_type[0] != STRING_RESULT ||
args->arg_type[1] != INT_RESULT)
{
strcpy(message,"XXX() requires a string and an integer");
return 1;
}
As an alternative to requiring your function's arguments to be of
particular types, you can use the initialisation function to set the
arg_type elements to the types you want. This causes MySQL to
coerce arguments to those types for each call to xxx(). For
example, to specify coercion of the first two arguments to string and integer,
do this in xxx_init(): args->arg_type[0] = STRING_RESULT; args->arg_type[1] = INT_RESULT;
char **args
args->args communicates information to the initialisation
function about the general nature of the arguments your function was called
with. For a constant argument i, args->args[i]
points to the argument value. (See below for instructions on how to access the
value properly.) For a non-constant argument, args->args[i] is
0. A constant argument is an expression that uses only constants,
such as 3 or 4*7-2 or SIN(3.14). A
non-constant argument is an expression that refers to values that may change
from row to row, such as column names or functions that are called with
non-constant arguments. For each invocation of the main function,
args->args contains the actual arguments that are passed for
the row currently being processed. Functions can refer to an argument
i as follows:
STRING_RESULT is given as a string
pointer plus a length, to allow handling of binary data or data of arbitrary
length. The string contents are available as args->args[i]
and the string length is args->lengths[i]. You should not
assume that strings are null-terminated.
INT_RESULT, you must cast
args->args[i] to a long long value: long long int_val; int_val = *((long long*) args->args[i]);
REAL_RESULT, you must cast
args->args[i] to a double value: double real_val; real_val = *((double*) args->args[i]);
unsigned long *lengths
lengths array indicates
the maximum string length for each argument. You should not change these. For
each invocation of the main function, lengths contains the actual
lengths of any string arguments that are passed for the row currently being
processed. For arguments of types INT_RESULT or
REAL_RESULT, lengths still contains the maximum
length of the argument (as for the initialisation function). The initialisation function should return 0 if no error occurred
and 1 otherwise. If an error occurs, xxx_init() should
store a null-terminated error message in the message parameter. The
message will be returned to the client. The message buffer is
MYSQL_ERRMSG_SIZE characters long, but you should try to keep the
message to less than 80 characters so that it fits the width of a standard
terminal screen.
The return value of the main function xxx() is the function
value, for long long and double functions. A string
functions should return a pointer to the result and store the length of the
string in the length arguments.
Set these to the contents and length of the return value. For example:
memcpy(result, "result string", 13); *length = 13;
The result buffer that is passed to the calc function is 255
byte big. If your result fits in this, you don't have to worry about memory
allocation for results.
If your string function needs to return a string longer than 255 bytes, you
must allocate the space for it with malloc() in your
xxx_init() function or your xxx() function and free it
in your xxx_deinit() function. You can store the allocated memory
in the ptr slot in the UDF_INIT structure for reuse by
future xxx() calls. See section 9.2.2.1
UDF Calling Sequences for simple functions.
To indicate a return value of NULL in the main function, set
is_null to 1:
*is_null = 1;
To indicate an error return in the main function, set the error
parameter to 1:
*error = 1;
If xxx() sets *error to 1 for any row,
the function value is NULL for the current row and for any
subsequent rows processed by the statement in which XXX() was
invoked. (xxx() will not even be called for subsequent rows.)
Note: In MySQL versions prior to 3.22.10, you should set both
*error and *is_null:
*error = 1; *is_null = 1;
Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF file `udf_example.cc' that is included in the MySQL source distribution. This file contains the following functions:
metaphon() returns a metaphon string of the string argument.
This is something like a soundex string, but it's more tuned for English.
myfunc_double() returns the sum of the ASCII values of the
characters in its arguments, divided by the sum of the length of its
arguments.
myfunc_int() returns the sum of the length of its arguments.
sequence([const int]) returns an sequence starting from the
given number or 1 if no number has been given.
lookup() returns the IP number for a hostname.
reverse_lookup() returns the hostname for an IP number. The
function may be called with a string "xxx.xxx.xxx.xxx" or four
numbers. A dynamically loadable file should be compiled as a sharable object file, using a command something like this:
shell> gcc -shared -o udf_example.so myfunc.cc
You can easily find out the correct compiler options for your system by running this command in the `sql' directory of your MySQL source tree:
shell> make udf_example.o
You should run a compile command similar to the one that make
displays, except that you should remove the -c option near the end
of the line and add -o udf_example.so to the end of the line. (On
some systems, you may need to leave the -c on the command.)
Once you compile a shared object containing UDFs, you must install it and
tell MySQL about it. Compiling a shared object from `udf_example.cc'
produces a file named something like `udf_example.so' (the exact name
may vary from platform to platform). Copy this file to some directory searched
by ld, such as `/usr/lib'. On many systems, you can set
the LD_LIBRARY or LD_LIBRARY_PATH environment variable
to point at the directory where you have your UDF function files. The
dlopen manual page tells you which variable you should use on your
system. You should set this in mysql.server or
safe_mysqld and restart mysqld.
After the library is installed, notify mysqld about the new
functions with these commands:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE AGGREGATE FUNCTION avgcost RETURNS REAL SONAME "udf_example.so";
Functions can be deleted using DROP FUNCTION:
mysql> DROP FUNCTION metaphon; mysql> DROP FUNCTION myfunc_double; mysql> DROP FUNCTION myfunc_int; mysql> DROP FUNCTION lookup; mysql> DROP FUNCTION reverse_lookup; mysql> DROP FUNCTION avgcost;
The CREATE FUNCTION and DROP FUNCTION statements
update the system table func in the mysql database.
The function's name, type and shared library name are saved in the table. You
must have the insert and delete privileges for
the mysql database to create and drop functions.
You should not use CREATE FUNCTION to add a function that has
already been created. If you need to reinstall a function, you should remove it
with DROP FUNCTION and then reinstall it with CREATE
FUNCTION. You would need to do this, for example, if you recompile a new
version of your function, so that mysqld gets the new version.
Otherwise the server will continue to use the old version.
Active functions are reloaded each time the server starts, unless you start
mysqld with the --skip-grant-tables option. In this
case, UDF initialisation is skipped and UDFs are unavailable. (An active
function is one that has been loaded with CREATE FUNCTION and not
removed with DROP FUNCTION.)
The procedure for adding a new native function is described below. Note that you cannot add native functions to a binary distribution because the procedure involves modifying MySQL source code. You must compile MySQL yourself from a source distribution. Also note that if you migrate to another version of MySQL (for example, when a new version is released), you will need to repeat the procedure with the new version.
To add a new native MySQL function, follow these steps:
sql_functions[] array.
sql_functions[] array
and add a function that creates a function object in
`item_create.cc'. Take a look at "ABS" and
create_funcs_abs() for an example of this. If the function
prototype is complicated (for example takes a variable number of arguments),
you should add two lines to `sql_yacc.yy'. One indicates the
preprocessor symbol that yacc should define (this should be added
at the beginning of the file). Then define the function parameters and add an
``item'' with these parameters to the simple_expr parsing rule.
For an example, check all occurrences of ATAN in
`sql_yacc.yy' to see how this is done.
Item_num_func or Item_str_func, depending on whether
your function returns a number or a string.
double Item_func_newname::val() longlong Item_func_newname::val_int() String *Item_func_newname::Str(String *str)If you inherit your object from any of the standard items (like
Item_num_func you probably only have to define one of the above
functions and let the parent object take care of the other functions. For
example, the Item_str_func class defines a val()
function that executes atof() on the value returned by
::str().
void Item_func_newname::fix_length_and_dec()This function should at least calculate
max_length based on
the given arguments. max_length is the maximum number of
characters the function may return. This function should also set
maybe_null = 0 if the main function can't return a
NULL value. The function can check if any of the function
arguments can return NULL by checking the arguments
maybe_null variable. You can take a look at
Item_func_mod::fix_length_and_dec for a typical example of how to
do this. All functions must be thread safe (in other words, don't use any global or static variables in the functions without protecting them with mutexes).
If you want to return NULL, from ::val(),
::val_int() or ::str() you should set
null_value to 1 and return 0.
For ::str() object functions, there are some additional
considerations to be aware of:
String *str argument provides a string buffer that may be
used to hold the result. (For more information about the String
type, take a look at the `sql_string.h' file.)
::str() function should return the string that holds the
result or (char*) 0 if the result is NULL.
In MySQL, you can define a procedure in C++ that can access and modify the
data in a query before it is sent to the client. The modification can be done on
row-by-row or GROUP BY level.
We have created an example procedure in MySQL Version 3.23 to show you what can be done.
Additionally we recommend you to take a look at mylua. With this
you can use the LUA language to load a procedure at runtime into
mysqld.
analyse([max elements,[max memory]])
This procedure is defined in the `sql/sql_analyse.cc'. This examines the result from your query and returns an analysis of the results:
max elements (default 256) is the maximum number of distinct
values analyse will notice per column. This is used by
analyse to check if the optimal column type should be of type
ENUM.
max memory (default 8192) is the maximum memory
analyse should allocate per column while trying to find all
distinct values. SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])
For the moment, the only documentation for this is the source.
You can find all information about procedures by examining the following files:
This chapter lists some common problems and error messages that users have run into. You will learn how to figure out what the problem is, and what to do to solve it. You will also find proper solutions to some common problems.
When you run into problems, the first thing you should do is to find out which program / piece of equipment is causing problems:
kbd_mode -a on it.
top,
ps, taskmanager, or some similar program, to check
which program is taking all CPU or is locking the machine.
top, df, or a similar program if you
are out of memory, disk space, open files, or some other critical resource.
If after you have examined all other possibilities and you have concluded that it's the MySQL server or a MySQL client that is causing the problem, it's time to do a bug report for our mailing list or our support team. In the bug report, try to give a very detailed description of how the system is behaving and what you think is happening. You should also state why you think it's MySQL that is causing the problems. Take into consideration all the situations in this chapter. State any problems exactly how they appear when you examine your system. Use the 'cut and paste' method for any output and/or error messages from programs and/or log files!
Try to describe in detail which program is not working and all symptoms you see! We have in the past received many bug reports that just state "the system doesn't work". This doesn't provide us with any information about what could be the problem.
If a program fails, it's always useful to know:
top. Let the
program run for a while, it may be evaluating something heavy.
mysqld server that is causing problems, can you
do mysqladmin -u root ping or mysqladmin -u root
processlist?
mysql, for example)
when you try to connect to the MySQL server? Does the client jam? Do you get
any output from the program? When sending a bug report, you should of follow the outlines described in this manual. See section 1.6.2.2 Asking Questions or Reporting Bugs.
This section lists some errors that users frequently get. You will find descriptions of the errors, and how to solve the problem here.
Access denied ErrorSee section 4.2.5
How the Privilege System Works, and especially. See section 4.2.10
Causes of Access denied Errors.
MySQL server has gone away ErrorThis section also covers the related Lost connection to server during
query error.
The most common reason for the MySQL server has gone away error
is that the server timed out and closed the connection. By default, the server
closes the connection after 8 hours if nothing has happened. You can change the
time limit by setting the wait_timeout variable when you start
mysqld.
Another common reason to receive the MySQL server has gone away
error is because you have issued a ``close'' on your MySQL connection and then
tried to run a query on the closed connection.
You can check that the MySQL hasn't died by executing mysqladmin
version and examining the uptime.
If you have a script, you just have to issue the query again for the client to do an automatic reconnection.
You normally can get the following error codes in this case (which one you get is OS-dependent):
| Error code | Description |
CR_SERVER_GONE_ERROR |
The client couldn't send a question to the server. |
CR_SERVER_LOST |
The client didn't get an error when writing to the server, but it didn't get a full answer (or any answer) to the question. |
You can also get these errors if you send a query to the server that is
incorrect or too large. If mysqld gets a packet that is too large
or out of order, it assumes that something has gone wrong with the client and
closes the connection. If you need big queries (for example, if you are working
with big BLOB columns), you can increase the query limit by
starting mysqld with the -O max_allowed_packet=#
option (default 1M). The extra memory is allocated on demand, so
mysqld will use more memory only when you issue a big query or when
mysqld must return a big result row!
Can't connect to [local] MySQL
server errorA MySQL client on Unix can connect to the mysqld server in two
different ways: Unix sockets, which connect through a file in the file system
(default `/tmp/mysqld.sock') or TCP/IP, which connects through a port
number. Unix sockets are faster than TCP/IP but can only be used when connecting
to a server on the same computer. Unix sockets are used if you don't specify a
hostname or if you specify the special hostname localhost.
On Windows you can connect only with TCP/IP if the mysqld server
is running on Win95/Win98. If it's running on NT, you can also connect with
named pipes. The name of the named pipe is MySQL. If you don't give a hostname
when connecting to mysqld, a MySQL client will first try to connect
to the named pipe, and if this doesn't work it will connect to the TCP/IP port.
You can force the use of named pipes on Windows by using . as the
hostname.
The error (2002) Can't connect to ... normally means that there
isn't a MySQL server running on the system or that you are using a wrong socket
file or TCP/IP port when trying to connect to the mysqld server.
Start by checking (using ps or the task manager on Windows) that
there is a process running named mysqld on your server! If there
isn't any mysqld process, you should start one. See section 2.4.2
Problems Starting the MySQL Server.
If a mysqld process is running, you can check the server by
trying these different connections (the port number and socket pathname might be
different in your setup, of course):
shell> mysqladmin version shell> mysqladmin variables shell> mysqladmin -h `hostname` version variables shell> mysqladmin -h `hostname` --port=3306 version shell> mysqladmin -h 'ip for your host' version shell> mysqladmin --socket=/tmp/mysql.sock version
Note the use of backquotes rather than forward quotes with the
hostname command; these cause the output of hostname
(that is, the current hostname) to be substituted into the
mysqladmin command.
Here are some reasons the Can't connect to local MySQL server
error might occur:
mysqld is not running.
mysqld uses the
MIT-pthreads package. See section 2.2.2
Operating Systems Supported by MySQL. However, all MIT-pthreads versions
doesn't support Unix sockets. On a system without sockets support you must
always specify the hostname explicitly when connecting to the server. Try
using this command to check the connection to the server: shell> mysqladmin -h `hostname` version
mysqld uses (default
`/tmp/mysqld.sock'). You might have a cron job that
removes the MySQL socket (for example, a job that removes old files from the
`/tmp' directory). You can always run mysqladmin version
and check that the socket mysqladmin is trying to use really
exists. The fix in this case is to change the cron job to not
remove `mysqld.sock' or to place the socket somewhere else. See
section A.4.5
How to Protect or change the MySQL socket file `/tmp/mysql.sock'.
mysqld server with the
--socket=/path/to/socket option. If you change the socket
pathname for the server, you must also notify the MySQL clients about the new
path. You can do this by providing the socket path as an argument to the
client. See section A.4.5
How to Protect or change the MySQL socket file `/tmp/mysql.sock'.
mysqld threads (for example, with the
mysql_zap script before you can start a new MySQL server. See
section A.4.1
What To Do If MySQL Keeps Crashing.
mysqld so that it uses a directory that you can access. If you get the error message Can't connect to MySQL server on
some_hostname, you can try the following things to find out what the
problem is :
telnet your-host-name
tcp-ip-port-number and press Enter a couple of times. If there is a
MySQL server running on this port you should get a responses that includes the
version number of the running MySQL server. If you get an error like
telnet: Unable to connect to remote host: Connection refused,
then there is no server running on the given port.
mysqld daemon on the local machine and
check the TCP/IP port that mysqld it's configured to use
(variable port) with mysqladmin variables.
mysqld server is not started with the
--skip-networking option. Host '...' is blocked ErrorIf you get an error like this:
Host 'hostname' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'
this means that mysqld has gotten a lot
(max_connect_errors) of connect requests from the host
'hostname' that have been interrupted in the middle. After
max_connect_errors failed requests, mysqld assumes
that something is wrong (like an attack from a cracker), and blocks the site
from further connections until someone executes the command mysqladmin
flush-hosts.
By default, mysqld blocks a host after 10 connection errors. You
can easily adjust this by starting the server like this:
shell> safe_mysqld -O max_connect_errors=10000 &
Note that if you get this error message for a given host, you should first
check that there isn't anything wrong with TCP/IP connections from that host. If
your TCP/IP connections aren't working, it won't do you any good to increase the
value of the max_connect_errors variable!
Too many connections ErrorIf you get the error Too many connections when you try to
connect to MySQL, this means that there is already max_connections
clients connected to the mysqld server.
If you need more connections than the default (100), then you should restart
mysqld with a bigger value for the max_connections
variable.
Note that mysqld actually allows
(max_connections+1) clients to connect. The last connection is
reserved for a user with the process privilege. By not giving
this privilege to normal users (they shouldn't need this), an administrator with
this privilege can log in and use SHOW PROCESSLIST to find out what
could be wrong. See section 4.5.6
SHOW Syntax.
The maximum number of connects MySQL is depending on how good the thread library is on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing.
Some non-transactional changed tables
couldn't be rolled back ErrorIf you get the error/warning: Warning: Some non-transactional changed
tables couldn't be rolled back when trying to do a ROLLBACK,
this means that some of the tables you used in the transaction didn't support
transactions. These non-transactional tables will not be affected by the
ROLLBACK statement.
The most typical case when this happens is when you have tried to create a
table of a type that is not supported by your mysqld binary. If
mysqld doesn't support a table type (or if the table type is
disabled by a startup option) , it will instead create the table type with the
table type that is most resembles to the one you requested, probably
MyISAM.
You can check the table type for a table by doing:
SHOW TABLE STATUS LIKE 'table_name'. See section 4.5.6.2
SHOW TABLE STATUS.
You can check the extensions your mysqld binary supports by
doing:
show variables like 'have_%'. See section 4.5.6.4
SHOW VARIABLES.
Out of memory ErrorIf you issue a query and get something like the following error:
mysql: Out of memory at line 42, 'malloc.c' mysql: needed 8136 byte (8k), memory in use: 12481367 bytes (12189k) ERROR 2008: MySQL client ran out of memory
note that the error refers to the MySQL client mysql. The reason
for this error is simply that the client does not have enough memory to store
the whole result.
To remedy the problem, first check that your query is correct. Is it
reasonable that it should return so many rows? If so, you can use mysql
--quick, which uses mysql_use_result() to retrieve the
result set. This places less of a load on the client (but more on the server).
Packet too large ErrorWhen a MySQL client or the mysqld server gets a packet bigger
than max_allowed_packet bytes, it issues a Packet too
large error and closes the connection.
A communication packet is a single SQL statement sent to the MySQL server or a single row that is sent to the client.
When a MySQL client or the mysqld server gets a packet bigger
than max_allowed_packet bytes, it issues a Packet too
large error and closes the connection. With some clients, you may also
get Lost connection to MySQL server during query error if the
communication packet is too big.
Note that both the client and the server has it's own
max_allowed_packet variable. If you want to handle big packets, you
have to increase this variable both in the client and in the server.
It's safe to increase this variable as memory is only allocated when needed; This variable is more a precaution to catch wrong packets between the client/server and also to ensure that you don't accidently use big packets so that you run out of memory.
If you are using the mysql client, you may specify a bigger
buffer by starting the client with mysql
--set-variable=max_allowed_packet=8M. Other clients have different
methods to set this variable.
You can use the option file to set max_allowed_packet to a
larger size in mysqld. For example, if you are expecting to store
the full length of a MEDIUMBLOB into a table, you'll need to start
the server with the set-variable=max_allowed_packet=16M option.
You can also get strange problems with large packets if you are using big
blobs, but you haven't given mysqld access to enough memory to
handle the query. If you suspect this is the case, try adding ulimit -d
256000 to the beginning of the safe_mysqld script and
restart mysqld.
Starting with MySQL 3.23.40 you only get the Aborted
connection error of you start mysqld with
--warnings.
If you find errors like the following in your error log.
010301 14:38:23 Aborted connection 854 to db: 'users' user: 'josh'
See section 4.9.1 The Error Log.
This means that something of the following has happened:
mysql_close() before exit.
wait_timeout or
interactive_timeout without doing any requests. See section 4.5.6.4
SHOW VARIABLES.
When the above happens, the server variable Aborted_clients is
incremented.
The server variable Aborted_connects is incremented when:
connect_timeout seconds to get a
connect package. Note that the above could indicate that someone is trying to break into your database!
See section 4.5.6.4
SHOW VARIABLES.
Other reasons for problems with Aborted clients / Aborted connections.
max_allowed_packet is too small or queries require more
memory than you have alloacated for mysqld. See section A.2.8
Packet too large Error. The table is full ErrorThis error occurs in older MySQL versions when an in-memory temporary table
becomes larger than tmp_table_size bytes. To avoid this problem,
you can use the -O tmp_table_size=# option to mysqld
to increase the temporary table size or use the SQL option
SQL_BIG_TABLES before you issue the problematic query. See section
5.5.6
SET Syntax.
You can also start mysqld with the --big-tables
option. This is exactly the same as using SQL_BIG_TABLES for all
queries.
In MySQL Version 3.23, in-memory temporary tables will automatically be
converted to a disk-based MyISAM table after the table size gets
bigger than tmp_table_size.
Can't create/write to file ErrorIf you get an error for some queries of type:
Can't create/write to file '\\sqla3fe_0.ism'.
this means that MySQL can't create a temporary file for the result set in the
given temporary directory. (The above error is a typical error message on
Windows, and the Unix error message is similar.) The fix is to start
mysqld with --tmpdir=path or to add to your option
file:
[mysqld] tmpdir=C:/temp
assuming that the `c:\\temp' directory exists. See section 4.1.2 my.cnf Option Files.
Check also the error code that you get with perror. One reason
may also be a disk full error;
shell> perror 28 Error code 28: No space left on device
Commands out of sync Error in
ClientIf you get Commands out of sync; You can't run this command now
in your client code, you are calling client functions in the wrong order!
This can happen, for example, if you are using
mysql_use_result() and try to execute a new query before you have
called mysql_free_result(). It can also happen if you try to
execute two queries that return data without a mysql_use_result()
or mysql_store_result() in between.
Ignoring user ErrorIf you get the following error:
Found wrong password for user: 'some_user@some_host'; Ignoring
user
this means that when mysqld was started or when it reloaded the
permissions tables, it found an entry in the user table with an
invalid password. As a result, the entry is simply ignored by the permission
system.
Possible causes of and fixes for this problem:
mysqld with an old
user table. You can check this by executing mysqlshow mysql
user to see if the password field is shorter than 16 characters. If so,
you can correct this condition by running the
scripts/add_long_password script.
mysqld with the --old-protocol option. Update the
user in the user table with a new password or restart
mysqld with --old-protocol.
user
table without using the PASSWORD() function. Use
mysql to update the user in the user table with a
new password. Make sure to use the PASSWORD() function: mysql> update user set password=PASSWORD('your password')
where user='XXX';
Table 'xxx' doesn't exist
ErrorIf you get the error Table 'xxx' doesn't exist or Can't
find file: 'xxx' (errno: 2), this means that no table exists in the
current database with the name xxx.
Note that as MySQL uses directories and files to store databases and tables, the database and table names are case sensitive! (On Windows the databases and tables names are not case sensitive, but all references to a given table within a query must use the same case!)
You can check which tables you have in the current database with SHOW
TABLES. See section 4.5.6
SHOW Syntax.
Can't initialize character set
xxx errorIf you get an error like:
MySQL Connection Failed: Can't initialize character set xxx
This means one of the following things:
--with-charset=xxx or with
--with-extra-charsets=xxx. See section 2.3.3
Typical configure Options. All standard MySQL binaries are
compiled with --with-extra-character-sets=complex which will
enable support for all multi-byte character sets. See section 4.6.1
The Character Set Used for Data and Sorting.
mysqld and the character set definition files is not in the place
where the client expect to find them. In this case you need to:
configure Options.
--character-sets-dir=path-to-charset-dir option.
If you get ERROR '...' not found (errno: 23), Can't open
file: ... (errno: 24), or any other error with errno 23 or
errno 24 from MySQL, it means that you haven't allocated enough
file descriptors for MySQL. You can use the perror utility to get a
description of what the error number means:
shell> perror 23 File table overflow shell> perror 24 Too many open files shell> perror 11 Resource temporarily unavailable
The problem here is that mysqld is trying to keep open too many
files simultaneously. You can either tell mysqld not to open so
many files at once or increase the number of file descriptors available to
mysqld.
To tell mysqld to keep open fewer files at a time, you can make
the table cache smaller by using the -O table_cache=32 option to
safe_mysqld (the default value is 64). Reducing the value of
max_connections will also reduce the number of open files (the
default value is 90).
To change the number of file descriptors available to
mysqld, you can use the option --open-files-limit=# to
safe_mysqld or -O open-files-limit=# to
mysqld. See section 4.5.6.4
SHOW VARIABLES. The easiest way to do that is to add the option
to your option file. See section 4.1.2
my.cnf Option Files. If you have an old mysqld version that
doesn't support this, you can edit the safe_mysqld script. There is
a commented-out line ulimit -n 256 in the script. You can remove
the '#' character to uncomment this line, and change the number 256
to affect the number of file descriptors available to mysqld.
ulimit (and open-files-limit) can increase the
number of file descriptors, but only up to the limit imposed by the operating
system. There is also a 'hard' limit that can only be overrided if you start
safe_mysqld or mysqld as root (just remember that you
need to also use the --user=.. option in this case). If you need to
increase the OS limit on the number of file descriptors available to each
process, consult the documentation for your operating system.
Note that if you run the tcsh shell, ulimit will
not work! tcsh will also report incorrect values when you ask for
the current limits! In this case you should start safe_mysqld with
sh!
If you are linking your program and you get errors for unreferenced symbols
that start with mysql_, like the following:
/tmp/ccFKsdPa.o: In function `main': /tmp/ccFKsdPa.o(.text+0xb): undefined reference to `mysql_init' /tmp/ccFKsdPa.o(.text+0x31): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x57): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x69): undefined reference to `mysql_error' /tmp/ccFKsdPa.o(.text+0x9a): undefined reference to `mysql_close'
you should be able to solve this by adding -Lpath-to-the-mysql-library
-lmysqlclient last on your link line.
If you get undefined reference errors for the
uncompress or compress function, add -lz
last on your link line and try again!
If you get undefined reference errors for functions that should
exist on your system, like connect, check the man page for the
function in question, for which libraries you should add to the link line!
If you get undefined reference errors for functions that don't
exist on your system, like the following:
mf_format.o(.text+0x201): undefined reference to `__lxstat'
it usually means that your library is compiled on a system that is not 100 % compatible with yours. In this case you should download the latest MySQL source distribution and compile this yourself. See section 2.3 Installing a MySQL Source Distribution.
If you are trying to run a program and you then get errors for unreferenced
symbols that start with mysql_ or that the mysqlclient
library can't be found, this means that your system can't find the share
libmysqlclient.so library.
The fix for this is to tell your system to search after shared libraries where the library is located by one of the following methods:
libmysqlclient.so the LD_LIBRARY_PATH environment
variable.
libmysqlclient.so the LD_LIBRARY environment
variable.
libmysqlclient.so to some place that is searched by your
system, like `/lib', and update the shared library information by
executing ldconfig. Another way to solve this problem is to link your program statically, with
-static, or by removing the dynamic MySQL libraries before linking
your code. In the second case you should be sure that no other programs are
using the dynamic libraries!
The MySQL server mysqld can be started and run by any user. In
order to change mysqld to run as a Unix user
user_name, you must do the following:
mysqladmin shutdown).
user_name
has privileges to read and write files in them (you may need to do this as the
Unix root user): shell> chown -R user_name /path/to/mysql/datadirIf directories or files within the MySQL data directory are symlinks, you'll also need to follow those links and change the directories and files they point to.
chown -R may not follow symlinks for you.
user_name, or, if you are using
MySQL Version 3.22 or later, start mysqld as the Unix
root user and use the --user=user_name option.
mysqld will switch to run as the Unix user user_name
before accepting any connections.
user line that specifies the user name to the
[mysqld] group of the `/etc/my.cnf' option file or the
`my.cnf' option file in the server's data directory. For example: [mysqld] user=user_name
At this point, your mysqld process should be running fine and
dandy as the Unix user user_name. One thing hasn't changed, though:
the contents of the permissions tables. By default (right after running the
permissions table install script mysql_install_db), the MySQL user
root is the only user with permission to access the
mysql database or to create or drop databases. Unless you have
changed those permissions, they still hold. This shouldn't stop you from
accessing MySQL as the MySQL root user when you're logged in as a
Unix user other than root; just specify the -u root
option to the client program.
Note that accessing MySQL as root, by supplying -u
root on the command line, has nothing to do with MySQL running
as the Unix root user, or, indeed, as another Unix user. The access
permissions and user names of MySQL are completely separate from Unix user
names. The only connection with Unix user names is that if you don't provide a
-u option when you invoke a client program, the client will try to
connect using your Unix login name as your MySQL user name.
If your Unix box itself isn't secured, you should probably at least put a
password on the MySQL root users in the access tables. Otherwise,
any user with an account on that machine can run mysql -u root
db_name and do whatever he likes.
If you have problems with file permissions, for example, if
mysql issues the following error message when you create a table:
ERROR: Can't find file: 'path/with/filename.frm' (Errcode: 13)
then the environment variable
UMASK might be set incorrectly when mysqld starts up.
The default umask value is 0660. You can change this behavior by
starting safe_mysqld as follows:
shell> UMASK=384 # = 600 in octal shell> export UMASK shell> /path/to/safe_mysqld &
By default MySQL will create database
and RAID directories with permission type 0700. You can modify this
behavior by setting the UMASK_DIR variable. If you set this, new
directories are created with the combined UMASK and
UMASK_DIR. For example, if you want to give group access to all new
directories, you can do:
shell> UMASK_DIR=504 # = 770 in octal shell> export UMASK_DIR shell> /path/to/safe_mysqld &
In MySQL Version 3.23.25 and above, MySQL assumes that the value for
UMASK and UMASK_DIR is in octal if it starts with a
zero.
See section F Environment Variables.
All MySQL versions are tested on many platforms before they are released. This doesn't mean that there aren't any bugs in MySQL, but it means if there are bugs, they are very few and can be hard to find. If you have a problem, it will always help if you try to find out exactly what crashes your system, as you will have a much better chance of getting this fixed quickly.
First, you should try to find out whether the problem is that the
mysqld daemon dies or whether your problem has to do with your
client. You can check how long your mysqld server has been up by
executing mysqladmin version. If mysqld has died, you
may find the reason for this in the file
`mysql-data-directory/`hostname`.err'. See section 4.9.1 The
Error Log.
Many crashes of MySQL are caused by corrupted index / data files. MySQL will
update the data on disk, with the write() system call, after every
SQL statement and before the client is notified about the result. (This is not
true if you are running with delayed_key_writes, in which case only
the data is written.) This means that the data is safe even if
mysqld crashes, as the OS will ensure that the not flushed data is
written to disk. You can force MySQL to sync everything to disk after every SQL
command by starting mysqld with --flush.
The above means that normally you shouldn't get corrupted tables unless:
mysqld or the machine in the middle
of an update.
mysqld that caused it to die in the
middle of an update.
mysqld servers on the same data on a
system that doesn't support good file system locks (normally handled by the
lockd daemon ) or if you are running multiple servers with
--skip-locking
mysqld confused.
ALTER TABLE on a repaired copy
of the table! Because it is very difficult to know why something is crashing, first try to check whether or not things that work for others crash for you. Please try the following things:
mysqld daemon with mysqladmin
shutdown, run myisamchk --silent --force */*.MYI on all
tables, and restart the mysqld daemon. This will ensure that you
are running from a clean state. See section 4
MySQL Database Administration.
mysqld --log and try to determine from the information in
the log whether or not some specific query kills the server. About 95% of all
bugs are related to a particular query! Normally this is one of the last
queries in the log file just before MySQL restarted. See section 4.9.2
The General Query Log. If you can repeatadly kill MySQL with one of the
queries, even when you have checked all tables just before doing the query,
then you have been able to locate the bug and should do a bug report for this!
See section 1.6.2.3
How to Report Bugs or Problems.
fork_test.pl and fork2_test.pl.
--with-debug option or --with-debug=full to
configure and then recompile. See section E.1
Debugging a MySQL server.
--skip-locking option to mysqld. On some
systems, the lockd lock manager does not work properly; the
--skip-locking option tells mysqld not to use
external locking. (This means that you cannot run 2 mysqld
servers on the same data and that you must be careful if you use
myisamchk, but it may be instructive to try the option as a
test.)
mysqladmin -u root processlist when
mysqld appears to be running but not responding? Sometimes
mysqld is not comatose even though you might think so. The
problem may be that all connections are in use, or there may be some internal
lock problem. mysqladmin processlist will usually be able to make
a connection even in these cases, and can provide useful information about the
current number of connections and their status.
mysqladmin -i 5 status or mysqladmin -i
5 -r status or in a separate window to produce statistics while you run
your other queries.
mysqld from gdb (or in another
debugger). See section E.1.3
Debugging mysqld under gdb.
mysqld has
crashed inside gdb: backtrace info local up info local up info localWith gdb you can also examine which threads exist with
info
threads and switch to a specific thread with thread #,
where # is the thread id. BLOB/TEXT columns (but only VARCHAR columns),
you can try to change all VARCHAR to CHAR with
ALTER TABLE. This will force MySQL to use fixed-size rows.
Fixed-size rows take a little extra space, but are much more tolerant to
corruption! The current dynamic row code has been in use at MySQL AB for at
least 3 years without any problems, but by nature dynamic-length rows are more
prone to errors, so it may be a good idea to try the above to see if it helps!
If you have forgotten the root user password for MySQL, you can
restore it with the following procedure:
mysqld server by sending a kill
(not kill -9) to the mysqld server. The pid is
stored in a .pid file, which is normally in the MySQL database
directory: kill `cat /mysql-data-directory/hostname.pid`You must be either the Unix
root user or the same user the
server runs as to do this.
mysqld with the --skip-grant-tables
option.
mysqld server with mysql -h hostname
mysql and change the password with a GRANT command. See
section 4.3.1
GRANT and REVOKE Syntax. You can also do this
with mysqladmin -h hostname -u user password 'new password'
mysqladmin -h hostname
flush-privileges or with the SQL command FLUSH PRIVILEGES.
Note that after you started mysqld with
--skip-grant-tables, any usage of GRANT commands will
give you an Unknown command error until you have executed
FLUSH PRIVILEGES.
When a disk-full condition occurs, MySQL does the following:
To alleviate the problem, you can take the following actions:
mysqladmin kill to the
thread. The thread will be aborted the next time it checks the disk (in 1
minute).
Exceptions to the above behaveour is when you use REPAIR or
OPTIMIZE or when the indexes are created in a batch after an
LOAD DATA INFILE or after an ALTER TABLE statement.
All of the above commands may use big temporary files that left to themself
would cause big problems for the rest of the system. If MySQL gets disk full
while doing any of the above operations, it will remove the big temporary files
and mark the table as crashed (except for ALTER TABLE, in which the
old table will be left unchanged).
MySQL uses the value of the TMPDIR environment variable as the
pathname of the directory in which to store temporary files. If you don't have
TMPDIR set, MySQL uses the system default, which is normally
`/tmp' or `/usr/tmp'. If the file system containing your
temporary file directory is too small, you should edit safe_mysqld
to set TMPDIR to point to a directory in a file system where you
have enough space! You can also set the temporary directory using the
--tmpdir option to mysqld.
MySQL creates all temporary files as hidden files. This ensures that the
temporary files will be removed if mysqld is terminated. The
disadvantage of using hidden files is that you will not see a big temporary file
that fills up the file system in which the temporary file directory is located.
When sorting (ORDER BY or GROUP BY), MySQL normally
uses one or two temporary files. The maximum disk-space needed is:
(length of what is sorted + sizeof(database pointer)) * number of matched rows * 2
sizeof(database pointer) is usually 4, but may grow in the
future for really big tables.
For some SELECT queries, MySQL also creates temporary SQL
tables. These are not hidden and have names of the form `SQL_*'.
ALTER TABLE creates a temporary table in the same directory as
the original table.
If you have problems with the fact that anyone can delete the MySQL
communication socket `/tmp/mysql.sock', you can, on most versions of
Unix, protect your `/tmp' file system by setting the
sticky bit on it. Log in as root and do the following:
shell> chmod +t /tmp
This will protect your `/tmp' file system so that files can be
deleted only by their owners or the superuser (root).
You can check if the sticky bit is set by executing ls -ld
/tmp. If the last permission bit is t, the bit is set.
You can change the place where MySQL uses / puts the socket file the following ways:
/etc/my.cnf: [client] socket=path-for-socket-file [mysqld] socket=path-for-socket-fileSee section 4.1.2 my.cnf Option Files.
safe_mysqld and most
clients with the --socket=path-for-socket-file option.
MYSQL_UNIX_PORT
environment variable.
configure option
--with-unix-socket-path=path-for-socket-file. See section 2.3.3
Typical configure Options. You can test that the socket works with this command:
shell> mysqladmin --socket=/path/to/socket version
If you have a problem with SELECT NOW() returning values in GMT
and not your local time, you have to set the TZ environment
variable to your current time zone. This should be done for the environment in
which the server runs, for example, in safe_mysqld or
mysql.server. See section F
Environment Variables.
By default, MySQL searches are case-insensitive (although there are some
character sets that are never case insensitive, such as czech).
That means that if you search with col_name LIKE 'a%', you will get
all column values that start with A or a. If you want
to make this search case-sensitive, use something like INSTR(col_name,
"A")=1 to check a prefix. Or use STRCMP(col_name, "A") = 0
if the column value must be exactly "A".
Simple comparison operations (>=, >, = , < , <=,
sorting and grouping) are based on each character's ``sort value''. Characters
with the same sort value (like E, e and é) are treated as the same character!
In older MySQL versions LIKE comparisons where done on the
uppercase value of each character (E == e but E <> é). In newer MySQL
versions LIKE works just like the other comparison operators.
If you want a column always to be treated in case-sensitive fashion, declare
it as BINARY. See section 6.5.3
CREATE TABLE Syntax.
If you are using Chinese data in the so-called big5 encoding, you want to
make all character columns BINARY. This works because the sorting
order of big5 encoding characters is based on the order of ASCII codes.
DATE ColumnsThe format of a DATE value is 'YYYY-MM-DD'.
According to ANSI SQL, no other format is allowed. You should use this format in
UPDATE expressions and in the WHERE clause of SELECT
statements. For example:
mysql> SELECT * FROM tbl_name WHERE date >= '1997-05-05';
As a convenience, MySQL automatically converts a date to a number if the date
is used in a numeric context (and vice versa). It is also smart enough to allow
a ``relaxed'' string form when updating and in a WHERE clause that
compares a date to a TIMESTAMP, DATE, or a
DATETIME column. (Relaxed form means that any punctuation character
may be used as the separator between parts. For example,
'1998-08-15' and '1998#08#15' are equivalent.) MySQL
can also convert a string containing no separators (such as
'19980815'), provided it makes sense as a date.
The special date '0000-00-00' can be stored and retrieved as
'0000-00-00'. When using a '0000-00-00' date through
MyODBC, it will automatically be converted to NULL
in MyODBC Version 2.50.12 and above, because ODBC can't handle
this kind of date.
Because MySQL performs the conversions described above, the following statements work:
mysql> INSERT INTO tbl_name (idate) VALUES (19970505);
mysql> INSERT INTO tbl_name (idate) VALUES ('19970505');
mysql> INSERT INTO tbl_name (idate) VALUES ('97-05-05');
mysql> INSERT INTO tbl_name (idate) VALUES ('1997.05.05');
mysql> INSERT INTO tbl_name (idate) VALUES ('1997 05 05');
mysql> INSERT INTO tbl_name (idate) VALUES ('0000-00-00');
mysql> SELECT idate FROM tbl_name WHERE idate >= '1997-05-05';
mysql> SELECT idate FROM tbl_name WHERE idate >= 19970505;
mysql> SELECT mod(idate,100) FROM tbl_name WHERE idate >= 19970505;
mysql> SELECT idate FROM tbl_name WHERE idate >= '19970505';
However, the following will not work:
mysql> SELECT idate FROM tbl_name WHERE STRCMP(idate,'19970505')=0;
STRCMP() is a string function, so it converts idate
to a string and performs a string comparison. It does not convert
'19970505' to a date and perform a date comparison.
Note that MySQL does no checking whether or not the date is correct. If you
store an incorrect date, such as '1998-2-31', the wrong date will
be stored. If the date cannot be converted to any reasonable value, a
0 is stored in the DATE field. This is mainly a speed
issue and we think it is up to the application to check the dates, and not the
server.
NULL ValuesThe concept of the NULL value is a common source of confusion
for newcomers to SQL, who often think that NULL is the same thing
as an empty string ''. This is not the case! For example, the
following statements are completely different:
mysql> INSERT INTO my_table (phone) VALUES (NULL);
mysql> INSERT INTO my_table (phone) VALUES ("");
Both statements insert a value into the phone column, but the
first inserts a NULL value and the second inserts an empty string.
The meaning of the first can be regarded as ``phone number is not known'' and
the meaning of the second can be regarded as ``she has no phone''.
In SQL, the NULL value is always false in comparison to any
other value, even NULL. An expression that contains
NULL always produces a NULL value unless otherwise
indicated in the documentation for the operators and functions involved in the
expression. All columns in the following example return NULL:
mysql> SELECT NULL,1+NULL,CONCAT('Invisible',NULL);
If you want to search for column values that are NULL, you
cannot use the =NULL test. The following statement returns no rows,
because expr = NULL is FALSE, for any expression:
mysql> SELECT * FROM my_table WHERE phone = NULL;
To look for NULL values, you must use the IS NULL
test. The following shows how to find the NULL phone number and the
empty phone number:
mysql> SELECT * FROM my_table WHERE phone IS NULL; mysql> SELECT * FROM my_table WHERE phone = "";
In MySQL, as in many other SQL servers, you can't index columns that can have
NULL values. You must declare such columns NOT NULL.
Conversely, you cannot insert NULL into an indexed column.
When reading data with LOAD DATA INFILE,
empty columns are updated with ''. If you want a NULL
value in a column, you should use \N in the text file. The literal
word 'NULL' may also be used under some circumstances. See section
6.4.9
LOAD DATA INFILE Syntax.
When using ORDER BY, NULL values are presented
first. If you sort in descending order using DESC,
NULL values are presented last. When using GROUP BY,
all NULL values are regarded as equal.
To help with NULL handling, you can use the IS NULL
and IS NOT NULL operators and the IFNULL() function.
For some column types, NULL values are handled
specially. If you insert NULL into the first TIMESTAMP
column of a table, the current date and time is inserted. If you insert
NULL into an AUTO_INCREMENT column, the next number in
the sequence is inserted.
aliasYou can use an alias to refer to a column in the GROUP BY,
ORDER BY, or in the HAVING part. Aliases can also be
used to give columns better names:
SELECT SQRT(a*b) as rt FROM table_name GROUP BY rt HAVING rt > 0; SELECT id,COUNT(*) AS cnt FROM table_name GROUP BY id HAVING cnt > 0; SELECT id AS "Customer identity" FROM table_name;
Note that ANSI SQL doesn't allow you to refer to an alias in a
WHERE clause. This is because when the WHERE code is
executed the column value may not yet be determined. For example, the following
query is illegal:
SELECT id,COUNT(*) AS cnt FROM table_name WHERE cnt > 0 GROUP BY id;
The WHERE statement is executed to determine which rows should
be included in the GROUP BY part while HAVING is used
to decide which rows from the result set should be used.
As MySQL doesn't support sub-selects or use of more than one table in the
DELETE statement, you should use the following approach to delete
rows from 2 related tables:
SELECT the rows based on some WHERE condition in
the main table.
DELETE the rows in the main table based on the same
condition.
DELETE FROM related_table WHERE related_column IN
(selected_rows). If the total number of characters in the query with
related_column is more than 1,048,576 (the default value of
max_allowed_packet, you should split it into smaller parts and
execute multiple DELETE statements. You will probably get the
fastest DELETE by only deleting 100-1000
related_column id's per query if the related_column is
an index. If the related_column isn't an index, the speed is
independent of the number of arguments in the IN clause.
If you have a complicated query that has many tables and that doesn't return any rows, you should use the following procedure to find out what is wrong with your query:
EXPLAIN and check if you can find
something that is obviously wrong. See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
WHERE clause.
LIMIT 10 with the
query.
SELECT for the column that should have matched a row
against the table that was last removed from the query.
FLOAT or DOUBLE columns
with numbers that have decimals, you can't use '='. This problem
is common in most computer languages because floating-point values are not
exact values. In most cases, changing the FLOAT to a
DOUBLE will fix this. See section A.5.7
Problems with floating point comparison.
mysql test < query.sql that shows your problems.
You can create a test file with mysqldump --quick database tables >
query.sql. Open the file in an editor, remove some insert lines (if
there are too many of these), and add your select statement at the end of the
file. Test that you still have your problem by doing: shell> mysqladmin create test2 shell> mysql test2 < query.sqlPost the test file using
mysqlbug to mysql@lists.mysql.com. Floating point numbers cause confusion sometimes, because these numbers are not stored as exact values inside computer architecture. What one can see on the screen usually is not the exact value of the number.
Field types FLOAT, DOUBLE and DECIMAL
are such.
CREATE TABLE t1 (i int, d1 decimal(9,2), d2 decimal(9,2)); INSERT INTO t1 values (1, 101.40, 21.40), (1, -80.00, 0.00), (2, 0.00, 0.00), (2, -13.20, 0.00), (2, 59.60, 46.40), (2, 30.40, 30.40), (3, 37.00, 7.40), (3, -29.60, 0.00), (4, 60.00, 15.40), (4, -10.60, 0.00), (4, -34.00, 0.00), (5, 33.00, 0.00), (5, -25.80, 0.00), (5, 0.00, 7.20), (6, 0.00, 0.00), (6, -51.40, 0.00); mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b FROM t1 GROUP BY i HAVING a <> b; +------+--------+-------+ | i | a | b | +------+--------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | | 6 | -51.40 | 0.00 | +------+--------+-------+
The result is correct. Although the first five records look like they shouldn't pass the comparison test, they may do so because the difference between the numbers show up around tenth decimal, or so depending on computer architecture.
The problem cannot be solved by using ROUND() (or similar function), because the result is still a floating point number. Example:
mysql> SELECT i, ROUND(SUM(d1), 2) AS a, ROUND(SUM(d2), 2) AS b FROM t1 GROUP BY i HAVING a <> b; +------+--------+-------+ | i | a | b | +------+--------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | | 6 | -51.40 | 0.00 | +------+--------+-------+
This is what the numbers in row 'a' look like:
mysql> SELECT i, ROUND(SUM(d1), 2)*1.0000000000000000 AS a, ROUND(SUM(d2), 2) AS b FROM t1 GROUP BY i HAVING a <> b; +------+----------------------+-------+ | i | a | b | +------+----------------------+-------+ | 1 | 21.3999999999999986 | 21.40 | | 2 | 76.7999999999999972 | 76.80 | | 3 | 7.4000000000000004 | 7.40 | | 4 | 15.4000000000000004 | 15.40 | | 5 | 7.2000000000000002 | 7.20 | | 6 | -51.3999999999999986 | 0.00 | +------+----------------------+-------+
Depending on the computer architecture you may or may not see similar results. Each CPU may evaluate floating point numbers differently. For example in some machines you may get 'right' results by multiplaying both arguments with 1, an example follows.
WARNING: NEVER TRUST THIS METHOD IN YOUR APPLICATION, THIS IS AN EXAMPLE OF A WRONG METHOD!!!
mysql> SELECT i, ROUND(SUM(d1), 2)*1 AS a, ROUND(SUM(d2), 2)*1 AS b FROM t1 GROUP BY i HAVING a <> b; +------+--------+------+ | i | a | b | +------+--------+------+ | 6 | -51.40 | 0.00 | +------+--------+------+
The reason why the above example seems to be working is that on the particular machine where the test was done, the CPU floating point arithmetics happens to round the numbers to same, but there is no rule that any CPU should do so, so it cannot be trusted.
The correct way to do floating point number comparison is to first decide on what is the wanted tolerance between the numbers and then do the comparsion against the tolerance number. For example, if we agree on that floating point numbers should be regarded the same, if they are same with precision of one of ten thousand (0.0001), the comparsion should be done like this:
mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b FROM t1 GROUP BY i HAVING ABS(a - b) > 0.0001; +------+--------+------+ | i | a | b | +------+--------+------+ | 6 | -51.40 | 0.00 | +------+--------+------+ 1 row in set (0.00 sec)
And vice versa, if we wanted to get rows where the numbers are the same, the test would be:
mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b FROM t1 GROUP BY i HAVING ABS(a - b) < 0.0001; +------+-------+-------+ | i | a | b | +------+-------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | +------+-------+-------+
ALTER TABLE.ALTER TABLE changes a table to the current character set. If you
during ALTER TABLE get a duplicate key error, then the cause is
either that the new character sets maps to keys to the same value or that the
table is corrupted, in which case you should run REPAIR TABLE on
the table.
If ALTER TABLE dies with an error like this:
Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17)
the problem may be that MySQL has crashed in a previous ALTER
TABLE and there is an old table named `A-something' or
`B-something' lying around. In this case, go to the MySQL data
directory and delete all files that have names starting with A- or
B-. (You may want to move them elsewhere instead of deleting them.)
ALTER TABLE works the following way:
If something goes wrong with the renaming operation, MySQL tries to undo the changes. If something goes seriously wrong (this shouldn't happen, of course), MySQL may leave the old table as `B-xxx', but a simple rename on the system level should get your data back.
The whole point of SQL is to abstract the application from the data storage format. You should always specify the order in which you wish to retrieve your data. For example:
SELECT col_name1, col_name2, col_name3 FROM tbl_name;
will return columns in the order col_name1,
col_name2, col_name3, whereas:
SELECT col_name1, col_name3, col_name2 FROM tbl_name;
will return columns in the order col_name1,
col_name3, col_name2.
You should never, in an application, use SELECT
* and retrieve the columns based on their position, because the order in
which columns are returned cannot be guaranteed over time. A
simple change to your database may cause your application to fail rather
dramatically.
If you want to change the order of columns anyway, you can do it as follows:
INSERT INTO new_table SELECT fields-in-new_table-order FROM
old_table.
old_table.
ALTER TABLE new_table RENAME old_table. The following are a list of the limitations with TEMPORARY
TABLES.
HEAP, ISAM
or MyISAM.
select * from temporary_table, temporary_table as t2;We plan to fix the above in 4.0.
RENAME on a TEMPORARY table. Note
that ALTER TABLE org_name RENAME new_name works! We plan to fix
the above in 4.0. Many users of MySQL have contributed very useful support tools and add-ons.
A list of what is available at http://mysql.com/Downloads/Contrib/ (or any mirror) is shown below.
Please visit our Software Portal at http://mysql.com/portal/software/. The community facilities there also allow for your input!
If you want to build MySQL support for the Perl
DBI/DBD interface, you should fetch the
Data-Dumper, DBI, and Msql-Mysql-modules
files and install them. See section 2.7
Perl Installation Comments.
Note: The programs listed here can be freely downloaded and used. They are copyrighted by their respective owners. Please see each product documentation for more details on licensing and terms. MySQL AB assumes no liability for the correctness of the information in this chapter or for the proper operation of the programs listed herein.
Data-Dumper module. Useful with
DBI/DBD support for older Perl installations.
DBI module.
DBD module to access mSQL and MySQL databases.
Data-ShowTable module. Useful with
DBI/DBD support.
libmysql.dll, by bsilva@umesd.k12.or.us.
TmySQL, a library to use MySQL with Delphi.
guile that allows guile to interact with
SQL databases. By Hal Roberts.
mydsn.dll. mydsn should be used to build
and remove the DSN registry file for the MyODBC driver in Coldfusion
applications. By Miguel Angel Solórzano.
PROCEDURE that can be loaded runtime.
user, db and
host tables. By Tim Sailer, modified by Atif Ghaffar aghaffar@artemedia.ch.
DBI:DBD and CGI.pm. FutureSQL allows one to
easily set up config files to view, edit, delete, and otherwise process
records from a MySQL database. It uses a data dictionary, configuration files
and templates, and allows "pre-processing" and "post-processing" on both
fields, records, and operations. DBI 1.06.
BLOB/TEXT columns
by Daniel Koch. mod_auth_mysql. This is a little tool that allows you
to add/change user records storing group and/or password entries in MySQL
tables. By Harry Brueckner, brueckner@respublica.de.
mod_auth_mysql. This is a two-part system for use with
mod_auth_mysql.
pam, using MySQL.
mysqldump output to a C header file. By Harry
Brueckner, brueckner@mail.respublica.de.
access_to_mysql.txt, except that this
one is fully configurable, has better type conversion (including detection of
TIMESTAMP fields), provides warnings and suggestions while
converting, quotes all special characters in text and binary
data, and so on. It will also convert to mSQL v1 and v2, and is
free of charge for anyone. See http://www.cynergi.net/exportsql/
for the latest version. By Pedro Freire, support@cynergi.net. NOTE: Doesn't work
with Access2!
exportsql. By Brian Andrews. NOTE:
Doesn't work with Access2!
exportsql.txt. That is,
it imports data from MySQL into an Access database via ODBC. This is very
handy when combined with exportsql, because it lets you use Access for all DB
design and administration, and synchronise with your actual MySQL server
either way. Free of charge. See http://www.netdive.com/freebies/importsql/
for any updates. Created by Laurent Bossavit of NetDIVE.
NOTE: Doesn't work with Access2!
mSQL to MySQL. By alfred@sb.net
mysqldump and pipe it to
the sqlconv.pl script. The script will parse through the
mysqldump output and will rearrange the fields so they can be
inserted into a new table. An example is when you want to create a new table
for a different site you are working on, but the table is just a bit different
(that is - fields in different order, etc.). By Steve Shreeve.
radiusd to make it support MySQL. By Wim Bonis, bonis@kiss.de. hylafax outgoing faxes in a MySQL database. By Sinisa
Milivojevic, sinisa@mysql.com.
This appendix lists the developers, contributors, and supporters that have helped to make MySQL what it is today.
These are the developers that are or have been employed by MySQL
AB to work on MySQL, roughly in the order they started to
work with us. Following each developer is a small list of the tasks that the
developer is responsible for, or the accomplishments they have made.
mysqld.
mysys library.
ISAM and MyISAM libraries (B-tree index
file handlers with index compression and different record formats).
HEAP library. A memory table system with our superior
full dynamic hashing. In use since 1981 and published around 1984.
replace program (take a look at it, it's
COOL!).
mSQL tools like msqlperl,
DBD/DBI, and DB2mysql.
texi2html.
mysys are left.
mysqlimport
mysql client.
PROCEDURE ANALYSE() zlib) in the client/server protocol.
INSERT
mysqldump -e option
LOAD DATA INFILE LOCAL
SQL_CALC_FOUND_ROWS SELECT option
--max-user-connections=... option
net_read and net_write_timeout
GRANT/REVOKE and SHOW GRANTS FOR
UNION.
DELETE/UPDATE
MySQLGUI client.
MySQL++. RAID support for MyISAM tables. SHOW CREATE TABLE.
MERGE library. ALTER TABLE ... ORDER BY ....
UPDATE ... ORDER BY ....
DELETE ... ORDER BY .... MyCC MySQL Control Center.
While MySQL AB owns all copyrights in the MySQL
server and the MySQL manual, we wish to recognise those who
have made contributions of one kind or another to the MySQL
distribution. Contributors are listed here, in somewhat random order:
mysqlshutdown.exe and
mysqlwatch.exe
mSQL, but found that it couldn't
satisfy our purposes so instead we wrote a SQL interface to our application
builder Unireg. mysqladmin and mysql ar programs
that were largely influenced by their mSQL counterparts. We have
put a lot of effort into making the MySQL syntax a superset of
mSQL. Many of the API's ideas are borrowed from mSQL
to make it easy to port free mSQL programs to MySQL. MySQL
doesn't contain any code from mSQL. Two files in the distribution
(`client/insert_test.c' and `client/select_test.c') are
based on the corresponding (non-copyrighted) files in the mSQL
distribution, but are modified as examples showing the changes necessary to
convert code from mSQL to MySQL. (mSQL is
copyrighted David J. Hughes.)
WHERE column REGEXP regexp.
gcc), the
libc library (from which we have borrowed `strto.c' to
get some code working in Linux), and the readline library (for
the mysql client).
mysqldump (previously msqldump, but ported and
enhanced by Monty).
DBD (Perl) interface.
mysqlhotcopy.
_MB character set macros and the ujis and sjis character
sets.
mysqlaccess, a program to show the access rights for a user.
xmysql, a graphical X client for MySQL.
DBD::mysql module.
FROM_UNIXTIME() time formatting, ENCRYPT()
functions, and bison advisor. Active mailing list member.
DBI/DBD. Have been of great help with
crash-me and running benchmarks. Some new date functions. The
mysql_setpermissions script.
DBI/DBD section in the
manual.
CREATE FUNCTION and
DROP FUNCTION.
AGGREGATE extension to UDF functions.
mysqlaccess more secure.
MERGE tables to handle INSERTS. Active
member on the MySQL mailing lists. Other contributors, bugfinders, and testers: James H. Thompson, Maurizio Menghini, Wojciech Tryc, Luca Berra, Zarko Mocnik, Wim Bonis, Elmar Haneke, jehamby@lightside, psmith@BayNetworks.com, duane@connect.com.au, Ted Deppner ted@psyber.com, Mike Simons, Jaakko Hyvatti.
And lots of bug report/patches from the folks on the mailing list.
A big tribute goes to those that help us answer questions on the
mysql@lists.mysql.com mailing list:
DBD-mysql questions.
xmysql-related questions and basic installation questions.
mysqlbug.
DBD, Linux, some SQL syntax questions. While MySQL AB owns all copyrights in the MySQL
server and the MySQL manual, we wish to recognise the
following companies, which helped us finance the development of the MySQL
server, such as by paying us for developing a new feature or giving us
hardware for development of the MySQL server.
mysqld version.
--skip-show-variables This appendix lists the changes from version to version in the MySQL source code.
Note that we tend to update the manual at the same time we make changes to MySQL. If you find a version listed below that you can't find on the MySQL download page (http://mysql.com/downloads/), this means that the version has not yet been released!
We are now working actively on MySQL 4.0 and will only provide critical bug fixes for MySQL 3.23. We will update this section as we add new features, so that others can follow our development.
Our TODO section contains what we plan to have in 4.0. See section 1.8.1 Things That Should be in 4.0.
HANDLER was used with some unsupported table
type.
mysqldump now puts ALTER TABLE table_name DISABLE
KEYS and ALTER TABLE table_name DISABLE KEYS in the sql
dump.
mysql_fix_extensions script
LOAD DATA FROM MASTER on OSF1.
des_encrypt() and des_decrypt().
--des-key-file.
HEX(string) now returns the characters in string converted to
hexadecimal.
GRANT when using
lower_case_table_names == 1.
SELECT ... IN SHARE MODE to SELECT .. LOCK IN
SHARE MODE (as in MySQL 3.23).
SELECT
queries.
MATCH ... AGAINST(... IN BOOLEAN MODE) can now work without
FULLTEXT index.
FULLTEXT indexes.
DELETE ... WHERE ... MATCH ....
MATCH ... AGAINST(... IN BOOLEAN MODE).
Note: you have to rebuild your tables with ALTER TABLE tablename
TYPE=MyISAM to be able to use boolean fulltext search.
LOCATE() and INSTR() are case sensitive if
neither argument is a binary string.
RND() initialization so that RND(N) and
RND(N+1) are more distinct.
UPDATE ... ORDER BY.
INSERT INTO .. SELECT to stop on errors by default.
DATA DIRECTORY and INDEX DIRECTORY
directives on Windows.
MODIFY and CHANGE in ALTER
TABLE to accept the AFTER keyword.
ORDER BY on a whole InnoDB table.
ft_min_word_len,
ft_max_word_len, and ft_max_word_len_for_sort.
libmysqld, the embedded MySQL server
library. Also added example programs (a mysql client and
mysqltest test program) which use libmysqld.
my_thread_init() and my_thread_end()
from mysql_com.h, and added mysql_thread_init() and
mysql_thread_end() to mysql.h.
BIGINT constants now work. MIN() and
MAX() now handle signed and unsigned BIGINT numbers
correctly.
latin_de which provides correct German
sorting.
TRUNCATE TABLE and DELETE FROM table_name are
now separate functions. One bonus is that DELETE FROM table_name
now returns the number of deleted rows.
DROP DATABASE now executes a DROP TABLE on all
tables in the database, which fixes a problem with InnoDB tables.
UNION.
DELETE can now operate on multiple tables.
HANDLER interface to MyISAM tables.
INSERT on MERGE tables. Patch
from Benjamin Pflugmann.
WEEK(#,0) to match the calendar in the USA.
COUNT(DISTINCT) is about 30% faster.
IS NULL, ISNULL() and some other
internal primitives.
myisam_bulk_insert_tree_size variable.
CHAR/VARCHAR) keys are now
much faster.
SELECT DISTINCT * from table_name ORDER
by key_part1 LIMIT #
SHOW CREATE TABLE now shows all table attributes.
ORDER BY ... DESC can now use keys.
LOAD DATA FROM MASTER "auto-magically" sets up a slave.
safe_mysqld to mysqld_safe.
MyISAM tables. Symlink
handling is now enabled by default for Windows.
LOAD DATA FROM MASTER "auto-magically" sets up a slave.
SQL_CALC_FOUND_ROWS and FOUND_ROWS(). This
makes it possible to know how many rows a query would have returned without a
LIMIT clause.
SHOW OPEN TABLES.
SELECT expression LIMIT ....
IDENTITY as a synonym for AUTO_INCREMENT
(like Sybase).
ORDER BY syntax to UPDATE and
DELETE.
SHOW INDEXES is now a synonym for SHOW INDEX.
ALTER TABLE table_name DISABLE KEYS and ALTER
TABLE table_name ENABLE KEYS commands.
IN instead of FROM in
SHOW commands.
FULLTEXT indexes.
REPAIR TABLE, ALTER TABLE, and OPTIMIZE
TABLE for tables with FULLTEXT indexes are now up to 100
times faster.
X'hexadecimal-number'
FLUSH TABLES WITH READ
LOCK
DATETIME = constant in WHERE
optimisation.
--master-data and --no-autocommit
to mysqldump (Thanks to Brian Aker for this).
mysql_explain_log.sh to distribution. (Thanks to
mobile.de). The 3.23 release has several major features that are not present in previous versions. We have added three new table types:
Note that only MyISAM is available in the standard binary distribution.
The 3.23 release also includes support for database replication between a master and many slaves, full-text indexing, and much more.
All new features are being developed in the 4.0 version. Only bug fixes and minor enhancements to existing features will be added to 3.23.
The replication code and BerkeleyDB code is still not as tested and as the rest of the code, so we will probably need to do a couple of future releases of 3.23 with small fixes for this part of the code. As long as you don't use these features, you should be quite safe with MySQL 3.23!
Note that the above doesn't mean that replication or Berkeley DB don't work; We have done a lot of testing of all code, including replication and BDB without finding any problems. It only means that not as many users use this code as the rest of the code and because of this we are not yet 100% confident in this code.
NULL in keys.
slave-skip-errors option
SHOW
STATUS is now much longer).
GROUP BY expr DESC works.
t1 LEFT JOIN t2 ON t2.key=constant.
mysql_config now also work with binary (relocated)
distributions. ORDER
BY on the whole table.
ANALYZE,REPAIR and
OPTIMIZE TABLE when the thread is waiting to get a lock on the
table.
ANALYZE TABLE.
INSERT
DELAYED which could cause the binary log to have rows that was not yet
written to MyISAM tables.
(UPDATE|DELETE) ...WHERE MATCH bugfix
--core-file now works on Solaris.
ALTER TABLE on a
TEMPORARY InnoDB table.
OPTIMIZE TABLE that reset index cardinality if
it was up to date.
t1 LEFT_JOIN t2 ... WHERE t2.date_column IS
NULL when date_column was declared as NOT NULL.
BLOB's.
MERGE tables on OS with 32 bit file pointers.
TIME_TO_SEC() when using negative values.
Rows_examined count in slow query log.
AVG() column in
HAVING.
DAYOFYEAR(column) will return NULL for
0000-00-00 dates.
SELECT * FROM date_col="2001-01-01" and date_col=time_col)
Can't write, because of unique
constraint with some GROUP BY queries.
CREATE ... FULLTEXT keys with other
table handlers than MyISAM.
signal() on Windows because this appears to not be
100 % reliable.
WHERE column_name=NULL on an indexed
column that had NULL values.
LEFT JOIN ... ON (column_name = constant) WHERE
column_name = constant.
%
could cause a core dump.
TCP_NODELAY was not used on some systems. (Speed problem).
The following changes are for InnoDB tables:
InnoDB variables to SHOW VARIABLES.
InnoDB tables.
DROP DATABASE now works also for InnoDB tables.
InnoDB now supports data files and raw disk partitions bigger
than 4 GB on those operating systems which have big files.
InnoDB calculates better table cardinality estimates for the
MySQL optimizer.
innodb_thread_concurrency
helps in performance tuning in heavily concurrent environments.
my.cnf parameter innodb_fast_shutdown
speeds up server shutdown.
my.cnf parameter innodb_force_recovery
helps to save your data in case the disk image of the database becomes
corrupt.
innodb_monitor has been improved and a new
innodb_table_monitor added.
MAX(col) is selected from an empty table,
and col is a not the first column in a multi-column index.
INSERT DELAYED and FLUSH TABLES
introduced in 3.23.42.
SELECT with many tables and multi-column indexes and 'range'
type.
EXPLAIN SELECT
when using many tables and ORDER BY.
LOAD DATA FROM MASTER when using table with
CHECKSUM=1.
BDB tables.
BDB tables and UNIQUE columns
defined as NULL.
myisampack when using pre-space filled
CHAR columns.
--safe-user-create. LOCK TABLES and BDB
tables.
REPAIR TABLE on MyISAM tables with row
lengths between 65517 - 65520 bytes
mysqladmin shutdown when there was
a lot of activity in other threads.
INSERT DELAYED where delay thread could be
hanging on upgrading locks without any apparent reasons.
myisampack and BLOB.
.MRG tables by hand. (Patch
from Benjamin Pflugmann).
MERGE table come from the same
database.
LOAD DATA INFILE and transactional tables.
INSERT DELAYED with wrong column
definition.
REPAIR of some particularly broken
tables.
InnoDB and AUTO_INCREMENT columns.
InnoDB and RENAME TABLE columns.
InnoDB and BLOB columns.
If one has used BLOB columns larger than 8000 bytes in an
InnoDB table, one must dump the table with
mysqldump, drop it and restore it from the dump.
InnoDB when one could get the error
Can't execute the given command... even when one didn't have an
active transaction.
ALTER TABLE). Now --lower_case_names
also works on Unix.
--sql-mode=option[,option[,option]]. See section
4.1.1
mysqld Command-line Options.
shutdown on Solaris where the
`.pid' file wasn't deleted.
doublewrite file flush method is used in
InnoDB. It reduces the need for Unix fsync calls to a fraction
and improves performance on most Unix flavors.
InnoDB Monitor to print a lot of
InnoDB state information, including locks, to the standard
output; useful in performance tuning.
InnoDB have been
fixed.
record_buffer to record_buffer and
record_rnd_buffer. To make things compatible to previous MySQL
versions, if record_rnd_buffer is not set, then it takes the
value of record_buffer.
ORDER BY where some ORDER
BY parts where wrongly removed.
ALTER TABLE and MERGE
tables.
my_thread_init() and
my_thread_end() to `mysql_com.h'
--safe-user-create to mysqld.
SELECT DISTINCT ... HAVING that casued error
message Can't find record in '#... --low-priority-updates and
INSERT's.
slave_wait_timeout for replication.
UPDATE and BDB tables.
BDB tables when using key parts.
GRANT FILE ON database.* ...;
Previously we added the DROP privilege for the database.
DELETE FROM table_name ... LIMIT 0 and UPDATE
FROM table_name ... LIMIT 0 acted as though the LIMIT
clause was not present (they deleted or updated all selected rows).
CHECK TABLE now checks if an AUTO_INCREMENT
column contains the value 0.
SIGHUP to mysqld will now only flush
the logs, not reset the replication.
1.0e1 (no sign after
e).
--force to myisamchk now also updates
states.
--warnings to mysqld. Now
mysqld only prints the error Aborted connection if
this option is used.
SHOW CREATE TABLE when you didn't have a
PRIMARY KEY.
innodb_unix_file_flush_method to
innodb_flush_method.
UNSIGNED BIGINT to
DOUBLE. This caused a problem when doing comparisons with
BIGINT values outside of the signed range.
BDB tables when querying empty tables.
COUNT(DISTINCT) with LEFT
JOIN and there wasn't any matching rows.
GEMINI table type.
GEMINI is not released under an Open Source license. AUTO_INCREMENT sequence wasn't reset when dropping and
adding an AUTO_INCREMENT column.
CREATE ... SELECT now creates non-unique indexes delayed.
LOCK TABLES table_name READ followed by
FLUSH TABLES put an exclusive lock on the table.
REAL @variables with was represented with 2 digits when
converted to strings.
LOAD TABLE FROM MASTER
failed.
myisamchk --fast --force will no longer repair tables
that only had the open count wrong.
-lcma thread library on HP-UX 10.20 so
that MySQL will be more stable on HP-UX.
IF() and number of decimals in the result.
INSERT DELAYED was waiting
for a LOCK TABLE.
InnoDB when tablespace was full.
MERGE tables and big tables (> 4G) when
using ORDER BY. SELECT from MERGE table
sometimes results in incorrectly ordered rows.
REPLACE() when using the ujis character set.
--skip-stack-trace to mysqld.
CREATE TEMPORARY now works with InnoDB tables.
InnoDB now promotes sub keys to whole keys.
CONCURRENT to LOAD DATA.
max_allowed_packet is too low
to read a very long log event from the master.
SELECT
DISTINCT ... HAVING.
SHOW CREATE TABLE now returns TEMPORARY for
temporary tables.
Rows_examined to slow query log.
WHERE that didn't match any rows.
mysqlcheck.
CHECK, REPAIR, OPTIMIZE.
InnoDB.
SELECT * FROM
table_name,table_name2 ... ORDER BY key_part1 LIMIT # will use index on
key_part1 instead of filesort.
LOCK TABLE to_table WRITE,...; INSERT INTO
to_table... SELECT ... when to_table was empty.
LOCK TABLE and BDB tables. MATCH in HAVING clause.
HEAP tables with LIKE.
--mysql-version to safe_mysqld
INNOBASE to InnoDB (because the
INNOBASE name was already used). All configure
options and mysqld start options are now using
innodb instead of innobase. This means that you have
to change any configuration files where you have used innobase
options before upgrading to this version!
CHAR(255) NULL columns.
master-host is not
set, as long as server-id is set and valid
master.info is present
SET SQL_SLAVE_SKIP_COUNTER=1; SLAVE START after a manual
sanity check/correction of data integrity.
REGEXP() on 64-bit machines.
UPDATE and DELETE with WHERE
unique_key_part IS NULL didn't update/delete all rows.
INSERT DELAYED for tables that support transactions.
TEXT/BLOB
column with wrong date format.
ALTER TABLE and LOAD DATA INFILE
that disabled key-sorting. These commands should now be faster in most cases.
FLUSH or REPAIR) would not use indexes for the
next query.
ALTER TABLE to InnoDB tables on FreeBSD.
mysqld variables myisam_max_sort_file_size
and myisam_max_extra_sort_file_size.
tis620 character set to make
comparisons case-independent and to fix a bug in LIKE for this
character set. Note: All tables that uses the
tis620 character set must be fixed with myisamchk -r
or REPAIR TABLE !
--skip-safemalloc option to mysqld.
mysqld is run as root.
FLUSH TABLES and
TEMPORARY tables. (Problem with freeing the key cache and error
Can't reopen table....)
latin1 and another problem when using many columns.
DISTINCT and summary functions.
SET TRANSACTION ISOLATION LEVEL ...
SELECT ... FOR UPDATE.
MySQL was compiled without transaction support.
UPDATE where keys weren't always used to find
the rows to be updated.
CONCAT_WS() where it returned wrong results.
CREATE ... INSERT and INSERT ... SELECT
to not allow concurrent inserts as this could make the binary log hard to
repeat. (Concurrent inserts are enabled if you are not using the binary or
update log.)
ORDER BY.
CLIENT_TRANSACTIONS.
SHOW VARIABLES when using INNOBASE
tables.
SELECT DISTINCT didn't
work.
SHOW ANALYZE for small tables.
INNOBASE
support to be compiled. INNOBASE table handler and the BDB
table handler to the MySQL source distribution.
GEMINI tables.
INSERT DELAYED that caused threads to hang
when inserting NULL into an AUTO_INCREMENT column.
CHECK TABLE / REPAIR TABLE that
could cause a thread to hang.
REPLACE will not replace a row that conflicts with an
auto_increment generated key.
mysqld now only sets CLIENT_TRANSACTIONS in
mysql->server_capabilities if the server supports a
transaction-safe handler.
LOAD DATA INFILE to allow numeric values to be read
into ENUM and SET columns.
ALTER TABLE ... ORDER BY.
max_user_connections to mysqld.
max_allowed_packet, not
the arbitrary limit of 4 MB.
= in argument to
--set-variable.
Waiting for table.
SHOW CREATE TABLE now dumps the UNION() for
MERGE tables.
ALTER TABLE now remembers the old UNION()
definition.
BDB table handler that occurred when using
an index on multi-part key where a key part may be NULL.
MAX() optimisation on sub-key for BDB
tables.
BDB tables and BLOB or TEXT fields when
joining many tables.
BDB tables and TEXT
columns.
BLOB key where a const row wasn't
found.
mysqlbinlog writes the timestamp value for each
query. This ensures that one gets same values for date functions like
NOW() when using mysqlbinlog to pipe the queries to
another server.
--skip-gemini, --skip-bdb and
--skip-innobase to mysqld even if these databases
are not compiled in mysqld.
GROUP BY ... DESC.
SET code, when one ran SET
@foo=bar, where bar is a column reference, an error was
not properly generated. --character-sets-dir to myisampack.
REPAIR TABLE ... EXTENDED.
GROUP BY on an
alias, where the alias was the same as an existing column name.
SEQUENCE() as an example UDF function.
mysql_install_db to use BINARY for
CHAR columns in the privilege tables.
TRUNCATE table_name to TRUNCATE TABLE
table_name to use the same syntax as Oracle. Until 4.0 we will also
allow TRUNCATE table_name to not crash old code.
MyISAM tables when a
BLOB was first part of a multi-part key.
CASE didn't work with GROUP BY.
--sort-recover to myisamchk.
myisamchk -S and OPTIMIZE TABLE now work on
Windows.
DISTINCT on results from functions that
referred to a group function, like: SELECT a, DISTINCT SEC_TO_TIME(sum(a)) from table_name GROUP BY a, b;
libmysqlclient library. Fixed bug in
handling STOP event after ROTATE event in
replication.
DROP DATABASE.
Table_locks_immediate and
Table_locks_waited status variables.
master.info. This fixes a bug introduced in 3.23.32.
SET SQL_SLAVE_SKIP_COUNTER=n command to recover from
replication glitches without a full database copy.
max_binlog_size variable; the binary log will be
rotated automatically when the size crosses the limit.
Last_error, Last_errno, and
Slave_skip_counter to SHOW SLAVE STATUS.
MASTER_POS_WAIT() function.
SIGILL, and SIGBUS
in addition to SIGSEGV.
mysqltest to take care of the timing issues in the
test suite.
ALTER TABLE can now be used to change the definition for a
MERGE table.
MERGE tables on Windows.
--temp-pool option to mysqld. Using this
option will cause most temporary files created to use a small set of names,
rather than a unique name for each new file. This is to work around a problem
in the Linux kernel dealing with creating a bunch of new files with different
names. With the old behavior, Linux seems to "leak" memory, as it's being
allocated to the directory entry cache instead of the disk cache. BACKUP, RESTORE, CHECK,
REPAIR, and ANALYZE TABLE.
FULL to SHOW COLUMNS. Now we show
the privilege list for the columns only if this option is given.
SHOW LOGS when there weren't any BDB logs.
mysql_list_fields().
This is to keep this code compatible with SHOW FIELDS.
MERGE tables didn't work on Windows.
SET PASSWORD=... on Windows.
TRIM("foo" from "foo") didn't return an empty string.
--with-version-suffix to configure.
mysql_close().
RESTORE TABLE when trying to restore from a
non-existent directory.
SET PASSWORD.
MASTER_POS_WAIT(). HAVING on an empty table could produce one result row
when it shouldn't.
HEAP tables on Windows.
SHOW TABLE STATUS didn't show correct average row length for
tables larger than 4G.
CHECK TABLE ... EXTENDED didn't check row links for fixed
size tables.
MEDIUM to CHECK TABLE.
DECIMAL() keys on negative numbers.
HOUR() (and some other TIME functions) on a
CHAR column always returned NULL.
setrlimit() on Linux to get -O
--open-files-limit=# to work on Linux.
mysqld variable: bdb_version.
SELECT ... FROM t1 LEFT JOIN t2 ON (t1.a=t2.a) WHERE t1.a=t2.aIn this case the test in the
WHERE clause was wrongly
optimised away.
MyISAM when deleting keys with possible
NULL values, but the first key-column was not a prefix-compressed
text column.
mysql.server to read the mysql.server
option section instead of mysql_server.
safe_mysqld and mysql.server to also read
the server option section.
Threads_created status variable to mysqld.
SHOW OPEN TABLES command.
myisamdump works against old mysqld
servers.
myisamchk -k# so that it works again.
LOCK TABLES will now automatically start a new transaction.
BDB tables to not use internal subtransactions and
reuse open files to get more speed.
--mysqld=# to safe_mysqld.
--fields-*-by and
--lines-terminated-by options to mysqldump and
mysqlimport. By Paul DuBois.
--safe-show-database to mysqld.
have_bdb, have_gemini,
have_innobase, have_raid and
have_openssl to SHOW VARIABLES to make it easy to
test for supported extensions.
--open-files-limit to mysqld.
--open-files to
--open-files-limit in safe_mysqld.
HEAP tables
that had many keys.
--bdb-no-sync works.
--bdb-recover to --bdb-no-recover as
recover should be on by default.
--skip-networking on Debian Linux.
UNOPENED in error messages.
SHOW LOGS queries.
<=> operator.
REPLACE with BDB tables.
LPAD() and RPAD() will shorten the result string
if it's longer than the length argument.
SHOW LOGS command.
PRIMARY keys first, followed by
UNIQUE keys.
UPDATE involving multi-part keys where one
specified all key parts both in the update and the WHERE part. In
this case MySQL could try to update a record that didn't match the whole
WHERE part.
mysqld to
report the hostname as '' in some error messages.
HEAP type tables; the variable
max_heap_table_size wasn't used. Now either MAX_ROWS
or max_heap_table_size can be used to limit the size of a
HEAP type table.
bdb_lock_max to bdb_max_lock.
auto_increment on sub-fields for BDB
tables.
ANALYZE of BDB tables.
ROLLBACK when you have updated a
non-transactional table you will get an error as a warning.
--bdb-shared-data to mysqld.
Slave_open_temp_tables.
binlog_cache_size and
max_binlog_cache_size to mysqld.
DROP TABLE, RENAME TABLE, CREATE
INDEX and DROP INDEX are now transaction endpoints.
DROP DATABASE on a symbolic linked database, both
the link and the original database is deleted.
DROP DATABASE works on OS/2.
SELECT DISTINCT ... table1 LEFT JOIN table2
... when table2 was empty.
--abort-slave-event-count and
--disconnect-slave-event-count options to mysqld for
debugging and testing of replication.
SHOW KEYS now shows whether or not key is
FULLTEXT.
mysqld processes.
mysql_print_defaults instead of various hacks to read the
`my.cnf' files. In addition, the handling of various paths has been
made more consistent with how mysqld handles them by default.
FULLTEXT indexes in one table.
REPAIR/OPTIMIZE.
Yuri Dario.
FLUSH TABLES table_name didn't always flush the index tree to
disk properly.
--bootstrap is now run in a separate thread. This fixes a
problem that caused mysql_install_db to core dump on some Linux
machines.
mi_create() to use less stack space.
MATCH when
used with UNIQUE key.
crash-me and the MySQL benchmarks to also work with
FrontBase.
RESTRICT and CASCADE after DROP
TABLE to make porting easier.
--slow-log.
connect_timeout to mysql and
mysqladmin.
connect_timeout as an alias for timeout
for option files read by mysql_options(). --pager[=...], --no-pager,
--tee=... and --no-tee to the mysql
client. The new corresponding interactive commands are pager,
nopager, tee and notee. See section 4.8.2 The
Command-line Tool, mysql --help and the interactive help for
more information.
MyISAM table failed.
SELECT, UPDATE and
INSERT statements running. The symptom was that the
UPDATE and INSERT queries were locked for a long
time while new SELECT statements were executed before the
updates.
options_files with mysql_options()
the return-found-rows option was ignored.
interactive-timeout in the option file
that is read by mysql_options(). This makes it possible to force
programs that run for a long time (like mysqlhotcopy) to use
interactive_timeout instead of wait_timeout.
--log-long-format then also queries that
do not use an index are logged, even if the query takes less than
long_query_time seconds.
LEFT JOIN which caused all columns in a
reference table to be NULL.
NATURAL JOIN without keys.
TEXT or BLOB.
DROP of temporary tables wasn't stored in the update/binary
log.
SELECT DISTINCT * ... LIMIT # only returned
one row.
strstr() for sparc and
cleaned up the `global.h' header file to avoid a problem with bad
aliasing with the compiler submitted with RedHat 7.0. (Reported by Trond
Eivind Glomsrød)
--skip-networking now works properly on NT.
ISAM tables when a row
with a length of more than 65K was shortened by a single byte.
MyISAM when running multiple updating
processes on the same table.
FLUSH TABLE tablename.
--replicate-ignore-table,
--replicate-do-table, --replicate-wild-ignore-table,
--replicate-wild-do-table.
IO_CACHE mechanism
instead of FILE to avoid OS problems when there are many files
open.
--open-files and --timezone to
safe_mysqld.
CREATE TEMPORARY TABLE ... SELECT ....
CREATE TABLE ... SELECT NULL.
large_file_support,net_read_timeout,
net_write_timeout and query_buffer_size to
SHOW VARIABLES.
created_tmp_files and
sort_merge_passes to SHOW STATUS.
FOREIGN
KEY definition.
TRUNCATE table_name as a synonym for DELETE FROM
table_name.
bdb_lock_max to mysqld.
mysql_connect() now aborts on Linux if the server doesn't
answer in timeout seconds.
SLAVE START did not work if you started with
--skip-slave-start and had not explicitly run CHANGE MASTER
TO.
SHOW MASTER STATUS to be consistent with
SHOW SLAVE STATUS. (It now has no directory in the log name.)
PURGE MASTER LOGS TO.
SHOW MASTER LOGS.
--safemalloc-mem-limit option to mysqld to
simulate memory shortage when compiled --with-debug=full.
SHOW SLAVE STATUS was using an uninitialised mutex if the
slave had not been started yet.
ELT() and MAKE_SET() when the query
used a temporary table.
CHANGE MASTER TO without specifying
MASTER_LOG_POS would set it to 0 instead of 4 and hit the magic
number in the master binlog.
ALTER TABLE ... ORDER BY ... syntax added. This will create
the new table with the rows in a specific order. SHOW CREATE when using
AUTO_INCREMENT columns.
mit-pthreads.
<> to work properly with NULL.
SUBSTRING_INDEX() and
REPLACE(). (Patch by Alexander Igonitchev)
CREATE TEMPORARY TABLE IF NOT EXISTS not to give an error
if the table exists.
PRIMARY KEY in a BDB table, a hidden
PRIMARY KEY will be created.
LEFT JOIN in some cases preferred a full table scan when
there was no WHERE clause.
--log-slow-queries, don't count the time waiting
for a lock.
MyISAM tables if you start
mysqld with --myisam-recover.
TYPE= keyword from CHECK and
REPAIR. Allow CHECK options to be combined. (You can
still use TYPE= but this usage is deprecated.)
--replicate-rewrite-db option to mysqld.
--skip-slave-start option to mysqld.
INSERT INTO
foo(some_key) values (1),(1)) erroneously terminated the slave thread.
DISTINCT is only used on
columns from some of the tables.
SHOW GRANTS didn't always show all column grants.
--default-extra-file=# to all MySQL clients.
INSERT statements now are initialised
properly.
UPDATE didn't always work when used with a range on a
timestamp that was part of the key that was used to find rows.
FULLTEXT index when inserting a
NULL column.
mkstemp() instead of tempnam().
Based on a patch from John Jones. databasename works as second argument to
mysqlhotcopy.
UMASK and UMASK_DIR can now be specified in
octal.
RIGHT JOIN. This makes RIGHT a reserved
word.
@@IDENTITY as a synonym for
LAST_INSERT_ID(). (This is for Visual Basic compatibility.)
myisamchk and REPAIR when using
FULLTEXT index.
LOAD DATA INFILE now works with FIFOs. (Patch by Toni L.
Harbaugh-Blackford.)
FLUSH LOGS broke replication if you specified a log name with
an explicit extension as the value of the log-bin option.
MyISAM with packed multi-part keys.
CHECK TABLE on Windows.
FULLTEXT index always used the koi8_ukr
character set.
CHECK TABLE.
MyISAM repair/reindex code didn't use the
--tempdir option for its temporary files.
BACKUP TABLE/RESTORE TABLE.
CHANGE MASTER TO when the slave did not
have the master to start with.
Time in the processlist for
Connect of the slave thread.
FLUSH MASTER if you didn't
specify a filename argument to --log-bin.
--memlock option to mysqld to lock
mysqld in memory on systems with the mlockall() call
(like in Solaris).
HEAP tables didn't use keys properly. (Bug from 3.23.23.)
MERGE tables (keys, mapping,
creation, documentation...). See section 7.2 MERGE
Tables.
mysqldump from 3.23 which caused some
CHAR columns not to be quoted.
analyze, check, optimize and
repair code.
OPTIMIZE TABLE is now mapped to REPAIR with
statistics and sorting of the index tree. This means that for the moment it
only works on MyISAM tables.
ORDER BY bug with BDB tables.
mysqld couldn't remove the
`.pid' file under Windows.
--log-isam to log MyISAM tables
instead of isam tables.
CHECK TABLE to work on Windows.
pwrite() safe on Windows. mysqld variable created_tmp_disk_tables.
TIMESTAMP(X) columns, MySQL now reports columns with
X other than 14 or 8 to be strings.
CHAR columns that may have characters with ASCII
values greater than 128 that was created or modified with 3.23.22 must be
repaired!
REPAIR TABLE or
myisamchk before use!
--core-file to mysqld to get a core
file on Linux if mysqld dies on the SIGSEGV signal.
mysql now starts with option
--no-named-commands (-g) by default. This option can
be disabled with --enable-named-commands (-G). This
may cause incompatibility problems in some cases, for example, in SQL scripts
that use named commands without a semicolon, etc. ! Long format commands still
work from the first line.
DROP TABLE statements
at the same time.
LEFT JOIN on an
empty table.
mysqld with incorrect
options.
free() bug in mysqlimport.
MyISAM index handling of
DECIMAL/NUMERIC keys.
MyISAM tables; In some
contexts, usage of MIN(key_part) or MAX(key_part)
returned an empty set.
mysqlhotcopy to use the new FLUSH TABLES
table_list syntax. Only tables which are being backed up are flushed
now.
--enable-thread-safe-client so that both
non-threaded (-lmysqlclient) and threaded
(-lmysqlclient_r) libraries are built. Users who linked against a
threaded -lmysqlclient will need to link against
libmysqlclient_r now.
RENAME command.
NULL in COUNT(DISTINCT
...).
ALTER TABLE, LOAD DATA INFILE on empty
tables and INSERT ... SELECT ... on empty tables to create
non-unique indexes in a separate batch with sorting. This will make the above
calls much faster when you have many indexes.
ALTER TABLE now logs the first used insert_id correctly.
BLOB column.
DATE_ADD/DATE_SUB where it returned a
datetime instead of a date.
***DEAD*** in SHOW PROCESSLIST.
pthread_rwlock_rdlock code.
SELECT on part keys works with BDB tables.
INSERT INTO bdb_table ... SELECT to work with BDB
tables.
CHECK TABLE now updates key statistics for the table.
ANALYZE TABLE will now only update tables that have been
changed since thee last ANALYZE. Note that this is a new feature
and tables will not be marked to be analysed until they are updated in any way
with 3.23.23 or newer. For older tables, you have to do CHECK
TABLE to update the key distribution.
CHECK,
ANALYZE, REPAIR and SHOW CREATE
commands.
CHANGE MASTER TO command.
FAST, QUICK EXTENDED check
types to CHECK TABLES.
myisamchk so that --fast and
--check-changed-tables are also honored with
--sort-index and --analyze.
LOAD TABLE FROM MASTER that did not lock
the table during index re-build.
LOAD DATA INFILE broke replication if the database was
excluded from replication.
SHOW SLAVE STATUS and SHOW MASTER
STATUS.
SLAVE STOP now will not return until the slave thread
actually exits.
MATCH function and
FULLTEXT index type (for MyISAM files). This makes
FULLTEXT a reserved word. lex_hash.h is created properly for each MySQL
distribution.
MASTER and COLLECTION are not
reserved words.
--slow-query-log didn't contain the
whole queries.
gcc 2.96 (intel) and
gcc 2.9 (Ia64) in gen_lex_hash.c.
host= in
the my.cnf file.
DATE_ADD()/DATE_SUB() against a number.
-F, --fast for myisamchk.
Added option -C, --check-only-changed to myisamchk.
ANALYZE table_name to update key statistics for tables.
0x... to be regarded as integers by
default.
SHOW PROCESSLIST.
auto-rehash on reconnect for the mysql
client.
MyISAM, where the index file
couldn't get bigger than 64M.
SHOW MASTER STATUS and SHOW SLAVE STATUS.
mysql_character_set_name(MYSQL *mysql) function to the
MySQL C API.
ASCII 0 safe.
mysql_config script.
< or > with a
char column that was only partly indexed.
mysqladmin to use the CREATE
DATABASE/DROP DATABASE commands instead of the old
deprecated API calls.
chown warning in safe_mysqld.
ORDER BY that was introduced in 3.23.19.
DELETE FROM tbl_name to do a drop+create of
the table if we are in AUTOCOMMIT mode (needed for BDB tables).
ISAM/MyISAM index files gets full during an
INSERT/UPDATE.
myisamchk didn't correctly update row checksum when used with
-ro (this only gave an warning in subsequent runs).
REPAIR TABLE so that it works with tables
without indexes.
DROP DATABASE
LOAD TABLE FROM MASTER is sufficiently bug-free to announce
it as a feature.
MATCH and AGAINST are now reserved words.
DELETE FROM tbl_name removed the .frm
file.
SHOW CREATE TABLE. MyISAM
table when doing update based on key on a table with many keys and some key
changed values.
ORDER BY can now uses REF keys to find subset
the rows that needs to be sorted.
print_defaults to
my_print_defaults to avoid name confusion.
NULLIF() to work according to ANSI SQL99.
net_read_timeout and net_write_timeout as
startup parameters to mysqld.
myisamchk
--sort-records on a table with prefix compressed index.
BEGIN WORK (the same as BEGIN).
ORDER BY on a
CONV() expression.
LOAD TABLE FROM MASTER
FLUSH MASTER and FLUSH SLAVE
FLUSH TABLES WITH READ LOCK to make a global lock
suitable to make a copy of MySQL data files.
CREATE TABLE ... SELECT ... PROCEDURE now works.
GROUP BY on VARCHAR/CHAR columns.
READ
and a WRITE lock.
RAID tables. find_in_set() when the first argument was
NULL.
LEFT JOIN and ORDER BY where
the first table had only one matching row.
my.cnf example files in the
`support-files' directory.
duplicated key problem when doing big GROUP
BY's. (This bug was probably introduced in 3.23.15.)
INNER JOIN to match ANSI SQL.
NATURAL JOIN syntax.
BDB interface.
--no-defaults and
--defaults-file to safe_mysqld.sh and
mysql_install_db.sh.
USE INDEX works with PRIMARY keys.
BEGIN statement to start a transaction in
AUTOCOMMIT mode.
KILL now works on a thread that is locked on a 'write' to a
dead client.
log-slave-updates to allow daisy-chaining
the slaves.
pthread_t is not the same as int.
INSERT DELAYED code when doing
ALTER TABLE.
INSERT DELAYED
TYPE=QUICK to CHECK and
REPAIR.
REPAIR TABLE when the table was in use by other
threads.
gdb when one does a lot of reconnects. This will also improve
systems where you can't use persistent connections.
UPDATE IGNORE will not abort if an update results in a
DUPLICATE_KEY error.
CREATE TEMPORARY TABLE commands in the update log.
delayed_key_writes tables and CHECK
TABLE.
replicate-do-db and replicate-ignore-db
options to restrict which databases get replicated
SQL_LOG_BIN option mysqld as root, you must now use the
--user=root option.
FLUSH TABLES command.
slow_launch_time variable and the
Slow_launch_threads status variable to mysqld. These
can be examined with mysqladmin variables and mysqladmin
extended-status.
INET_NTOA() and INET_ATON().
IF() now depends on the second and third
arguments and not only on the second argument.
myisamchk could go into a loop when trying to
repair a crashed table.
INSERT DELAYED to update log if
SQL_LOG_UPDATE=0.
REPLACE on HEAP tables.
SHOW
VARIABLES.
DELETE of many rows on a table with
compressed keys where MySQL scanned the index to find the rows.
CHECK on table with deleted keyblocks.
LAST_INSERT_ID() to
update a table with an auto_increment key.
NULLIF().
LOAD DATA INFILE on a table with
BLOB/TEXT columns.
EXPLAIN SELECT ... now also prints out whether MySQL needs to
create a temporary table or use file sorting when resolving the
SELECT.
ORDER BY parts where the part is a
constant expression in the WHERE part. Indexes can now be used
even if the ORDER BY doesn't match the index exactly, as long as
all the not used index parts and all the extra ORDER BY columns
are constants in the WHERE clause. See section 5.4.3
How MySQL Uses Indexes.
UPDATE and DELETE on a whole unique key in the
WHERE part, is now faster than before.
RAID_CHUNKSIZE to be in 1024 byte increments.
CONCAT() where one of the arguments was a
function that returned a modified argument.
myisamchk, where it updated the
header in the index file when one only checked the table. This confused the
mysqld daemon if it updated the same table at the same time. Now
the status in the index file is only updated if one uses
--update-state. With older myisamchk versions you
should use --read-only when only checking tables, if there is the
slightest chance that the mysqld server is working on the table
at the same time!
DROP TABLE is logged in the update log.
DECIMAL() key field where the
column data contained leading zeros.
myisamchk when the auto_increment isn't the first
key.
DATETIME in ISO8601 format: 2000-03-12T12:00:00
mysqld binary can now handle many
different character sets (you can choose which when starting
mysqld).
REPAIR TABLE.
mysql_thread_safe().
UMASK_DIR environment variable.
CONNECTION_ID().
= on BLOB or VARCHAR
BINARY keys, where only a part of the column was indexed, the whole
column of the result row wasn't compared.
ORDER BY.
GROUP BY part. LOCK TABLE command; This fixed the problem one got when
running the test-ATIS test with --fast or
--check-only-changed.
SQL_BUFFER_RESULT to SELECT.
CHECK TABLE command.
mysqladmin shutdown will wait for the local
server to close down.
print_defaults to the `.rpm' files. Removed
mysqlbug from the client `.rpm' file. MyISAM involving REPLACE ... SELECT
... which could give a corrupted table.
myisamchk where it wrongly reset the
auto_increment value.
DISTINCT on HEAP temporary tables to use
hashed keys to quickly find duplicated rows. This mostly concerns queries of
type SELECT DISTINCT ... GROUP BY .... This fixes a problem where
not all duplicates were removed in queries of the above type. In addition, the
new code is MUCH faster.
IF NOT EXISTS to CREATE DATABASE.
--all-databases and --databases to
mysqldump to allow dumping of many databases at the same time.
DECIMAL() index in
MyISAM tables.
mysqladmin shutdown on a local connection,
mysqladmin now waits until the pidfile is gone before
terminating.
COUNT(DISTINCT ...) queries.
myisamchk works properly with RAID:ed tables.
LEFT JOIN and key_field IS
NULL.
net_clear() which could give the error
Aborted connection in the MySQL clients.
USE INDEX (key_list) and IGNORE INDEX
(key_list) as join parameters in SELECT.
DELETE and RENAME should now work on
RAID tables. ALTER TABLE tbl_name ADD (field_list) syntax.
GRANT/REVOKE ALL PRIVILEGES doesn't affect
GRANT OPTION.
) from the output of SHOW GRANTS
UNIQUE INDEX in CREATE
statements.
mysqlhotcopy - fast on-line hot-backup utility for local
MySQL databases. By Tim Bunce.
mysqlaccess. Thanks to Steve Harvey for this.
--i-am-a-dummy and --safe-updates
to mysql.
select_limit and max_join_size
to mysql.
SQL_MAX_JOIN_SIZE and
SQL_SAFE_UPDATES.
READ LOCAL lock that doesn't lock the table for
concurrent inserts. (This is used by mysqldump.)
LOCK TABLES ... READ doesn't anymore allow
concurrent inserts.
--skip-delay-key-write to mysqld.
_rowid can now be used as an alias for an integer type unique
indexed column.
SIGPIPE when compiling with
--thread-safe-clients to make things safe for old clients.
LOCK TABLES. INSERT DELAYED.
date_column BETWEEN const_date AND const_date
works.
NULL in a table with
BLOB/TEXT columns.
WHERE K1=1 and K3=2 and (K2=2 and K4=4 or K2=3 and
K4=5)
source to mysql to allow reading
of batch files inside the mysql client. Original patch by Matthew
Vanecek.
WITH GRANT OPTION option.
GRANT error when using tables from
many databases in the same query.
SELECT when using many overlapping
indexes. MySQL should now be able to choose keys even better when there is
many keys to choose from.
=). For example, the following type of queries should now be
faster: SELECT * from key_part_1=const and key_part_2 > const2
VARCHAR columns to
CHAR columns didn't change row type from dynamic to fixed.
SELECT floor(pow(2,63)).
mysqld startup option --delay-key-write
to --delay-key-write-for-all-tables
read-next-on-key to HEAP tables. This
should fix all problems with HEAP tables when using not
UNIQUE keys.
--log-slow-queries to mysqld to log all
queries that take a long time to a separate log file with a time of how long
the query took.
WHERE key_column=RAND(...)
SELECT ... LEFT JOIN ... key_column IS
NULL, when key_column could contain NULL
values.
LOAD DATA
INFILE. NISAM.
ISAM when doing some ORDER BY ...
DESC queries.
--delay-key-write didn't enable delayed key writing.
TEXT column which only involved case changes.
INSERT DELAYED doesn't update timestamps that are
given.
YEARWEEK() and options x,
X, v and V to
DATE_FORMAT().
MAX(indexed_column) and HEAP tables.
BLOB NULL keys and LIKE
"prefix%".
MyISAM and fixed-length rows < 5 bytes.
GROUP BY queries.
ENUM
field value was too big. pthread_mutex_timedwait, which is used with INSERT
DELAYED. See section 2.6.1 Linux
Notes (All Linux Versions).
MyISAM with keys > 250 characters.
MyISAM one can now do an INSERT at the same
time as other threads are reading from the table.
max_write_lock_count to mysqld to
force a READ lock after a certain number of WRITE
locks.
delayed_key_write on show
variables.
concurrency to
thread_concurrency.
LOCATE(substr,str), POSITION(substr IN str),
LOCATE(substr,str,pos), INSTR(str,substr),
LEFT(str,len), RIGHT(str,len),
SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR
len), MID(str,pos,len), SUBSTRING(str,pos),
SUBSTRING(str FROM pos),
SUBSTRING_INDEX(str,delim,count), RTRIM(str),
TRIM([[BOTH | TRAILING] [remstr] FROM] str),
REPLACE(str,from_str,to_str), REVERSE(str),
INSERT(str,pos,len,newstr), LCASE(str),
LOWER(str), UCASE(str) and UPPER(str);
Patch by Wei He.
FULL to SHOW PROCESSLIST.
--verbose to mysqladmin.
REPLACE() and LOAD DATA
INFILE.
mysqld variable interactive_timeout.
mysql_data_seek() from
ulong to ulonglong. mysqld option -O
lower_case_table_names={0|1} to allow users to force table names to
lowercase.
SELECT ... INTO DUMPFILE.
mysqld option --ansi to make some
functions ANSI SQL compatible.
#sql.
` (" in
--ansi mode).
[floor() overflow safe on FreeBSD.
--quote-names to mysqldump
PRIMARY KEY NOT
NULL.
encrypt() to be thread safe and not reuse buffer.
mysql_odbc_escape_string() function to support big5
characters in MyODBC.
FLOAT and DOUBLE (without any
length modifiers) are not anymore fixed decimal point numbers.
FLOAT(X): Now this is the same as
FLOAT if X <= 24 and a DOUBLE if 24 < X <=
53.
DECIMAL(X) is now an alias for DECIMAL(X,0) and
DECIMAL is now an alias for DECIMAL(10,0). The same
goes for NUMERIC.
ROW_FORMAT={default | dynamic | static |
compressed} to CREATE_TABLE.
DELETE FROM table_name didn't work on temporary tables.
CHAR_LENGTH() to be multi-byte character
safe.
ORD(string). SELECT DISTINCT ... ORDER BY RAND().
ALTER TABLE + adding a column after the last field didn't
work.
CREATE TABLE foo (a int not null auto_increment, b char(5), primary key
(b,a))
NULL.
AS on fieldname with CREATE TABLE table_name SELECT
... didn't work.
NATIONAL and NCHAR when defining
character columns. This is the same as not using BINARY.
NULL columns in a PRIMARY KEY (only
in UNIQUE keys).
LAST_INSERT_ID if one uses this in ODBC: WHERE
auto_increment_column IS NULL. This seems to fix some problems with
Access.
SET SQL_AUTO_IS_NULL=0|1 now turns on/off the handling of
searching after the last inserted row with WHERE auto_increment_column
IS NULL.
mysqld variable concurrency for
Solaris.
--relative to mysqladmin to make
extended-status more useful to monitor changes.
COUNT(DISTINCT ...) on an empty table.
LOAD DATA INFILE and BLOB
columns.
~ (negation).
UDF functions. DATETIME into a TIME column will not
anymore try to store 'days' in it.
SUM().)
LIKE "%" on an index that may have
NULL values.
REVOKE ALL PRIVILEGES didn't revoke all privileges.
SHOW GRANTS FOR user (by Sinisa).
date_add syntax: date/datetime + INTERVAL #
interval_type. By Joshua Chamas.
LOAD DATA REPLACE.
REGEXP is now case insensitive if you use non-binary strings.
ASC is now the default again for ORDER BY.
LIMIT to UPDATE.
mysql_change_user().
SHOW VARIABLES.
--[whitespace] comments.
INSERT into tbl_name VALUES (), that is, you may now
specify an empty value list to insert a row in which each column is set to its
default value.
SUBSTRING(text FROM pos) to conform to ANSI SQL.
(Before this construct returned the rightmost 'pos' characters.)
SUM() with GROUP BY returned 0 on some systems.
SHOW TABLE STATUS.
DELAY_KEY_WRITE option to CREATE TABLE.
AUTO_INCREMENT on any key part.
YEAR(NOW()) and
YEAR(CURDATE()).
CASE construct.
COALESCE(). SELECT * FROM table_name WHERE key_part1
>= const AND (key_part2 = const OR key_part2 = const). The bug was
that some rows could be duplicated in the result.
myisamchk without -a updated the index
distribution wrong.
SET SQL_LOW_PRIORITY_UPDATES=1 gave parse error before.
WHERE
clause. UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100
SELECT ... WHERE key_part1=const1 AND
key_part_2=const2 AND key_part1=const4 AND key_part2=const4 ; Indextype
should be range instead of ref.
egcs 1.1.2 optimiser bug (when using
BLOBs) on Linux Alpha.
LOCK TABLES combined with DELETE
FROM table.
NULL and
BLOB/TEXT columns.
SELECT ... FROM t1 LEFT JOIN
t2 ON ... WHERE t2.not_null_column IS NULL.
ORDER BY and GROUP BY can be done on functions.
ORDER BY
RAND().
WHERE key_column = function.
WHERE key_column = column_name even
if the columns are not identically packed.
WHERE column_name IS NULL.
--init-file=file_name to mysqld.
COUNT(DISTINCT value, [value, ...])
CREATE TEMPORARY TABLE now creates a temporary table, in its
own namespace, that is automatically deleted if connection is dropped.
CASE): CASE, THEN,
WHEN, ELSE and END.
EXPORT_SET() and MD5().
MyISAM) with a lot of new
features. See section 7.1 MyISAM
Tables.
HEAP tables which are extremely fast
for lookups.
LOAD_FILE(filename) to get the contents of a
file as a string value.
<=> which will act as = but
will return TRUE if both arguments are NULL. This is useful for
comparing changes between tables.
EXTRACT(interval FROM datetime) function.
FLOAT(X) is not rounded on storage and may
be in scientific notation (1.0 E+10) when retrieved.
REPLACE is now faster than before.
LIKE character comparison to behave as
=; This means that 'e' LIKE ''e' (if the line
doesn't display correctly, the latter 'e' means a French 'e' with a dot above)
is now true.
SHOW TABLE STATUS returns a lot of information about the
tables.
LIKE to the SHOW STATUS command.
SHOW COLUMNS.
packed and comment to SHOW
INDEX.
CREATE TABLE ... COMMENT
"xxx").
UNIQUE, as in CREATE TABLE table_name (col int
not null UNIQUE)
CREATE TABLE table_name SELECT ...
CREATE TABLE IF NOT EXISTS ...
CHAR(0) columns.
DATE_FORMAT() now requires `%' before any format
character.
DELAYED is now a reserved word (sorry about that :( ).
analyse, file:
`sql_analyse.c'. This will describe the data in your query. Try the
following: SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])This procedure is extremely useful when you want to check the data in your table!
BINARY cast to force a string to be compared case
sensitively.
--skip-show-database to mysqld.
UPDATE now also works with
BLOB/TEXT columns.
INNER join syntax. NOTE: This made
INNER a reserved word!
IP/NETMASK syntax.
NOT NULL DATE/DATETIME column with IS
NULL, this is changed to a compare against 0 to satisfy
some ODBC applications. (By shreeve@uci.edu.)
NULL IN (...) now returns NULL instead of
0. This will ensure that null_column NOT IN (...)
doesn't match NULL values.
TIME columns.
TIME strings to be more strict. Now the
fractional second part is detected (and currently skipped). The following
formats are supported:
DATETIME.
LOW_PRIORITY attribute to LOAD DATA
INFILE.
LOAD DATA INFILE.
DECIMAL(x,y) now works according to ANSI SQL.
LAST_INSERT_ID() is now updated for INSERT INTO ...
SELECT.
SELECT DISTINCT is much faster; It uses the new
UNIQUE functionality in MyISAM. One difference
compared to MySQL Version 3.22 is that the output of DISTINCT is
not sorted anymore.
mysql_num_fields() on a MYSQL object, you must use
mysql_field_count() instead.
LIBEWRAP; Patch by Henning P . Schmiedehausen.
AUTO_INCREMENT for other than numerical columns.
AUTO_INCREMENT will now automatically make the column
NOT NULL.
NULL as the default value for AUTO_INCREMENT columns.
SQL_BIG_RESULT; SQL_SMALL_RESULT is now
default.
--enable-large-files/--disable-large-files switch to
configure. See `configure.in' for some systems where
this is automatically turned off because of broken implementations.
readline to 4.0.
CREATE TABLE options: PACK_KEYS and
CHECKSUM.
mysqld option --default-table-type.
The 3.22 version has faster and safer connect code than version 3.21, as well as a lot of new nice enhancements. The reason for not including these changes As there aren't really any major changes, upgrading from 3.21 to 3.22 should be very easy and painless. See section 2.5.3 Upgrading from Version 3.21 to Version 3.22.
STD().
ISAM library from 3.23.
INSERT DELAYED.
LEFT
JOIN/STRAIGHT_JOIN on a table with only one row. GROUP BY on TINYBLOB columns;
This caused bugzilla to not show rows in some queries.
LOCK TABLE
SELECT DISTINCT queries. mysqlhotcopy - fast on-line hot-backup utility for local
MySQL databases. By Tim Bunce.
mysqlaccess. Thanks to Steve Harvey for this.
GROUP functions.
ISAM code when deleting rows on tables
with packed indexes. SELECT when using many overlapping
indexes.
SELECT floor(pow(2,63)).
WITH GRANT OPTION option.
GROUP BY queries.
ENUM
field value was too big.
mysqlshutdown.exe and mysqlwatch.exe to
the Windows distribution.
ORDER BY on a reference key.
INSERT DELAYED doesn't update timestamps that are
given. LEFT JOIN and COUNT() on a
column which was declared NULL + and it had a
DEFAULT value.
CONCAT() in a
WHERE clause.
AVG() and STD() with
NULL values. ROUND() will now work on Windows. BLOB/TEXT column to
REVERSE().
/*! */ with version numbers.
SUBSTRING(text FROM pos) to conform to ANSI SQL.
(Before this construct returned the rightmost 'pos' characters.)
LOCK TABLES combined with DELETE
FROM table
SET SQL_LOW_PRIORITY_UPDATES=# didn't work.
GRANT ... IDENTIFIED BY
SELECT * FROM table_name WHERE
key_part1 >= const AND (key_part2 = const OR key_part2 = const)
DATA is not a reserved word anymore.
LOCK TABLES table_name READ; FLUSH
TABLES;
isamchk should now work on Windows.
libtool
1.3.2.
configure.
--defaults-file=### to option file handling to
force use of only one specific option file.
CREATE syntax to ignore MySQL Version 3.23 keywords.
INSERT DELAYED on a table
locked with LOCK TABLES.
DROP TABLE on a table that
was locked by another thread.
GRANT/REVOKE commands in the update log.
isamchk to detect a new error condition.
NATURAL LEFT JOIN. mysql_close()
directly after mysql_init().
delayed_insert_thread counting when you couldn't create
a new delayed_insert thread.
CONCAT() with many arguments.
DELETE FROM TABLE when table was locked by
another thread.
LEFT JOIN involving empty tables.
mysql.db column from char(32) to
char(60).
MODIFY and DELAYED are not reserved words
anymore.
TIME column.
Host '...' is not allowed to connect to this
MySQL server after one had inserted a new MySQL user with a
GRANT command.
TCP_NODELAY also on Linux (should give faster
TCP/IP connections). STD() for big tables when result should be 0.
INSERT DELAYED had some garbage at end in the update log.
mysql_install_db (from 3.22.17).
BLOB columns. shutdown all
threads didn't die properly.
-O flush_time=# to mysqld. This is
mostly useful on Windows and tells how often MySQL should close all unused
tables and flush all updated tables to disk.
VARCHAR column compared with
CHAR column didn't use keys efficiently. --log-update and
connecting without a default database.
configure and portability problems.
LEFT JOIN on tables that had circular dependencies
caused mysqld to hang forever. mysqladmin processlist could kill the server if a new user
logged in.
DELETE FROM tbl_name WHERE key_column=col_name didn't find
any matching rows. Fixed.
DATE_ADD(column, ...) didn't work.
INSERT DELAYED could deadlock with status 'upgrading lock'
ENCRYPT() to take longer salt strings than 2
characters.
longlong2str is now much faster than before. For Intel
x86 platforms, this function is written in optimised assembler.
MODIFY keyword to ALTER TABLE.
GRANT used with IDENTIFIED BY didn't take effect
until privileges were flushed.
SHOW STATUS.
ORDER BY with 'only index' optimisation
when there were multiple key definitions for a used column.
DATE and DATETIME columns are now up to 5 times
faster than before.
INSERT DELAYED can be used to let the client do other things
while the server inserts rows into a table.
LEFT JOIN USING (col1,col2) didn't work if one used it with
tables from 2 different databases.
LOAD DATA LOCAL INFILE didn't work in the Unix version
because of a missing file.
VARCHAR/BLOB on very short
rows (< 4 bytes); error 127 could occur when deleting rows.
BLOB/TEXT through formulas didn't work for short
(< 256 char) strings.
GRANT on a new host, mysqld could
die on the first connect from this host.
ORDER BY on column name that was the
same name as an alias.
BENCHMARK(loop_count,expression) function to time
expressions. mysqld to make it easier to start
from shell scripts.
TIMESTAMP column to NULL didn't record
the timestamp value in the update log.
INSERT INTO TABLE ... SELECT ...
GROUP BY.
localtime_r() on Windows so that it will
not crash anymore if your date is > 2039, but instead will return a time of
all zero.
^Z (ASCII 26) to \Z as
^Z doesn't work with pipes on Windows.
mysql_fix_privileges adds a new column to the
mysql.func to support aggregate UDF functions in future MySQL
releases. NOW(), CURDATE() or
CURTIME() directly in a column didn't work.
SELECT COUNT(*) ... LEFT JOIN ... didn't work with no
WHERE part.
pthread_cond() on the Windows
version. get_lock() now correctly times out on Windows! DATE_ADD() and
DATE_SUB() in a WHERE clause.
GRANT ... TO user
IDENTIFIED BY 'password' syntax.
GRANT checking with SELECT on many
tables.
mysql_fix_privilege_tables to the RPM
distribution. This is not run by default because it relies on the client
package.
SQL_SMALL_RESULT to SELECT to force
use of fast temporary tables when you know that the result set will be small.
DATE_ADD/DATE_SUB() doesn't have enough days.
GRANT compares columns in case-insensitive fashion.
ALTER TABLE
dump core in some contexts.
user@hostname can now include
`.' and `-' without quotes in the context of the
GRANT, REVOKE and SET PASSWORD FOR ...
statements.
isamchk for tables which need big temporary files.
mysql_fix_privilege_tables script when you upgrade to this
version! This is needed because of the new GRANT system. If you
don't do this, you will get Access denied when you try to use
ALTER TABLE, CREATE INDEX or DROP
INDEX.
GRANT to allow/deny users table and column access.
USER() to return user@host
PASSWORD for another user.
FLUSH STATUS that sets most status variables to
zero.
aborted_threads,
aborted_connects.
connection_timeout.
SET SQL_WARNINGS=1 to get a warning count also
for simple inserts.
SIGTERM instead of SIGQUIT with
shutdown to work better on FreeBSD.
\G (print vertically) to mysql.
SELECT HIGH_PRIORITY ... killed mysqld.
IS NULL on a AUTO_INCREMENT column in a
LEFT JOIN didn't work as expected.
MAKE_SET(). mysql_install_db no longer starts the MySQL server! You
should start mysqld with safe_mysqld after
installing it! The MySQL RPM will, however, start the server as before.
--bootstrap option to mysqld and recoded
mysql_install_db to use it. This will make it easier to install
MySQL with RPMs.
+, - (sign and minus), *,
/, %, ABS() and MOD() to
be BIGINT aware (64-bit safe).
ALTER TABLE that caused mysqld to
crash.
INSERT.)
INSERT INTO tbl_name SET col_name=value, col_name=value,
...
MYSQL_INIT_COMMAND to
mysql_options() to make a query on connect or reconnect.
MYSQL_READ_DEFAULT_FILE and
MYSQL_READ_DEFAULT_GROUP to mysql_options() to read
the following parameters from the MySQL option files: port,
socket, compress, password,
pipe, timeout, user,
init-command, host and database.
maybe_null to the UDF structure.
IGNORE to INSERT statements with
many rows.
isamchk -rq on each table that has an
index on a CHAR or VARCHAR column.
mysql_setpermission, by Luuk de Boer, allows one
to easily create new users with permissions for specific databases.
LOAD DATA INFILE).
SHOW STATUS and changed format of
output to be like SHOW VARIABLES.
extended-status command to mysqladmin
which will show the new status variables. SET SQL_LOG_UPDATE=0 caused a lockup of the server.
FLUSH [ TABLES | HOSTS | LOGS | PRIVILEGES ] [,
...]
KILL thread_id.
ALTER TABLE from a
INT to a short CHAR() column.
SELECT HIGH_PRIORITY; This will get a lock for the
SELECT even if there is a thread waiting for another
SELECT to get a WRITE LOCK.
LIKE on
BLOB/TEXT columns with \0.
ESCAPE option to LIKE.
mysqladmin debug.
mysqld on Windows with the
--flush option. This will flush all tables to disk after each
update. This makes things much safer on NT/Win98 but also
much slower. my_strcoll()! The patch should always be safe to install (for any
system), but as this patch changes ISAM internals it's not yet in the default
distribution.
DATE_ADD() and DATE_SUB() didn't work with group
functions.
mysql will now also try to reconnect on USE
DATABASE commands.
ORDER BY and LEFT JOIN and
const tables.
ORDER BY if the first ORDER
BY column was a key and the rest of the ORDER BY columns
wasn't part of the key.
OPTIMIZE TABLE.
DROP TABLE and mysqladmin
shutdown on Windows (a fatal bug from 3.22.6).
TIME columns and negative strings.
LIMIT clause for the DELETE statement.
/*! ... */ syntax to hide MySQL-specific
keywords when you write portable code. MySQL will parse the code inside the
comments as if the surrounding /*! and */ comment
characters didn't exist.
OPTIMIZE TABLE tbl_name can now be used to reclaim disk space
after many deletes. Currently, this uses ALTER TABLE to
regenerate the table, but in the future it will use an integrated
isamchk for more speed.
libtool to get the configure more portable.
UPDATE and DELETE operations when
using DATETIME or DATE keys.
mysqladmin proc to display information about
your own threads. Only users with the Process_priv privilege
can get information about all threads.
YYMMDD, YYYYMMDD,
YYMMDDHHMMSS for numbers when using DATETIME and
TIMESTAMP types. (Formerly these formats only worked with
strings.)
CLIENT_IGNORE_SPACE to allow use of
spaces after function names and before `(' (Powerbuilder requires
this). This will make all function names reserved words.
--log-long-format option to mysqld to
enable timestamps and INSERT_ID's in the update log.
--where option to mysqldump (patch by Jim
Faucette).
mysqldump.
LOAD DATA INFILE statement, you can now use the new
LOCAL keyword to read the file from the client.
mysqlimport will automatically use LOCAL when
importing with the TCP/IP protocol.
DROP TABLE, ALTER TABLE, DELETE FROM
TABLE and mysqladmin flush-tables under heavy usage.
Changed locking code to get better handling of locks of different types.
DBI to 1.00 and DBD to 1.2.0.
mysqld. (To avoid errors if you
accidentally try to use an old error message file.)
affected_rows(),
insert_id(), ...) are now of type BIGINT to allow
64-bit values to be used. This required a minor change in the MySQL protocol
which should affect only old clients when using tables with
AUTO_INCREMENT values > 16M.
mysql_fetch_lengths() has changed from
uint * to ulong *. This may give a warning for old
clients but should work on most machines.
mysys and dbug libraries to allocate all
thread variables in one struct. This makes it easier to make a threaded
`libmysql.dll' library.
gethostname() (instead of
uname()) when constructing `.pid' file names.
COUNT(), STD() and AVG() are
extended to handle more than 4G rows.
-838:59:59 <= x
<= 838:59:59 in a TIME column.
TIME column to too short a value, MySQL now assumes the value is
given as: [[[D ]HH:]MM:]SS instead of HH[:MM[:SS]].
TIME_TO_SEC() and SEC_TO_TIME() can now handle
negative times and hours up to 32767.
SET OPTION SQL_LOG_UPDATE={0|1} to allow
users with the process privilege to bypass the update log.
(Modified patch from Sergey A Mukhin violet@rosnet.net.)
LPAD().
BLOB
reading from pipes safer.
-O max_connect_errors=# option to mysqld.
Connect errors are now reset for each correct connection.
max_allowed_packet to
1M in mysqld.
--low-priority-updates option to mysqld,
to give table-modifying operations (INSERT, REPLACE,
UPDATE, DELETE) lower priority than retrievals. You
can now use {INSERT | REPLACE | UPDATE | DELETE} LOW_PRIORITY ...
You can also use SET OPTION SQL_LOW_PRIORITY_UPDATES={0|1} to
change the priority for one thread. One side effect is that
LOW_PRIORITY is now a reserved word. :(
INSERT INTO table ...
VALUES(...),(...),(...), to allow inserting multiple rows with a single
statement.
INSERT INTO tbl_name is now also cached when used with
LOCK TABLES. (Previously only INSERT ... SELECT and
LOAD DATA INFILE were cached.)
GROUP BY functions with HAVING: mysql> SELECT col FROM table GROUP BY col HAVING COUNT(*)>0;
mysqld will now ignore trailing `;' characters
in queries. This is to make it easier to migrate from some other SQL servers
that require the trailing `;'.
SELECT INTO
OUTFILE.
GREATEST() and LEAST() functions. You must now use
these instead of the MAX() and MIN() functions to
get the largest/smallest value from a list of values. These can now handle
REAL, BIGINT and string (CHAR or
VARCHAR) values.
DAYOFWEEK()
had offset 0 for Sunday. Changed the offset to 1.
GROUP BY columns and
fields when there is no GROUP BY specification.
--vertical option to mysql, for printing
results in vertical mode.
--tmpdir option to mysqld, for specifying
the location of the temporary file directory.
SELECT ... FROM table WHERE auto_increment_column IS NULLto:
SELECT ... FROM table WHERE auto_increment_column == LAST_INSERT_ID()This allows some ODBC programs (Delphi, Access) to retrieve the newly inserted row to fetch the
AUTO_INCREMENT id.
DROP TABLE now waits for all users to free a table before
deleting it.
BIN(), OCT(), HEX()
and CONV() for converting between different number bases.
SUBSTRING() with 2 arguments.
ORDER
BY and GROUP BY.
mysqld now automatically disables system locking on Linux and
Windows, and for systems that use MIT-pthreads. You can force the use of
locking with the --enable-locking option.
--console option to mysqld, to force a
console window (for error messages) when using Windows.
DATE_ADD() and DATE_SUB() functions.
mysql_ping() to the client library.
--compress option to all MySQL clients.
byte to char in `mysql.h' and
`mysql_com.h'. <<, >>,
RPAD() and LPAD().
ORDER BY to work when no records
are found when using fields that are not in GROUP BY (MySQL
extension).
--chroot option to mysqld, to start
mysqld in a chroot environment (by Nikki Chumakov nikkic@cityline.ru).
--one-thread option to mysqld, for
debugging with LinuxThreads (or glibc). (This replaces the
-T32 flag)
DROP TABLE IF EXISTS to prevent an error from occurring
if the table doesn't exist.
IF and EXISTS are now reserved words (they would
have to be sooner or later).
mysqldump.
mysql_ping().
mysql_init() and
mysql_options(). You now MUST call mysql_init()
before you call mysql_real_connect(). You don't have to call
mysql_init() if you only use mysql_connect().
mysql_options(...,MYSQL_OPT_CONNECT_TIMEOUT,...) so you
can set a timeout for connecting to a server.
--timeout option to mysqladmin, as a test
of mysql_options().
AFTER column and FIRST options to
ALTER TABLE ... ADD columns. This makes it possible to add a new
column at some specific location within a row in an existing table.
WEEK() now takes an optional argument to allow handling of
weeks when the week starts on Monday (some European countries). By default,
WEEK() assumes the week starts on Sunday.
TIME columns weren't stored properly (bug in MySQL Version
3.22.0).
UPDATE now returns information about how many rows were
matched and updated, and how many ``warnings'' occurred when doing the update.
FORMAT(-100,2).
ENUM and SET columns were compared in binary
(case-sensitive) fashion; changed to be case insensitive. mysql_real_connect() call is changed to: mysql_real_connect(MYSQL *mysql, const char *host, const char *user,
const char *passwd, const char *db, uint port,
const char *unix_socket, uint client_flag)
accept() thread. This fixes permanently the telnet bug that was a
topic on the mail list some time ago.
mysqld now has a local hostname
resolver cache so connections should actually be faster than before, even with
this feature.
tbl_name@db_name or db_name.tbl_name. This
makes it possible to give a user read access to some tables and write access
to others simply by keeping them in different databases!
--user option to mysqld, to allow it to
run as another Unix user (if it is started as the Unix root
user).
mysqladmin password 'new_password'. This uses encrypted passwords
that are not logged in the normal MySQL log!
SELECT code to handle some very specific queries
involving group functions (like COUNT(*)) without a GROUP
BY but with HAVING. The following now works: mysql> SELECT count(*) as C FROM table HAVING C > 1;
malloc().
-T32 option to mysqld, for running all
queries under the main thread. This makes it possible to debug
mysqld under Linux with gdb!
not_null_column IS NULL (needed for
some Access queries).
STRAIGHT_JOIN to be used between two tables to force
the optimiser to join them in a specific order.
VARCHAR rather than
CHAR and the column type is now VARCHAR for fields
saved as VARCHAR. This should make the MyODBC
driver better, but may break some old MySQL clients that don't handle
FIELD_TYPE_VARCHAR the same way as FIELD_TYPE_CHAR.
CREATE INDEX and DROP INDEX are now implemented
through ALTER TABLE. CREATE TABLE is still the
recommended (fast) way to create indexes.
--set-variable option wait_timeout to
mysqld.
mysqladmin processlist to show how long
a query has taken or how long a thread has slept.
show variables and some new to
show status.
YEAR. YEAR is stored in 1 byte
with allowable values of 0, and 1901 to 2155.
DATE type that is stored in 3 bytes rather than 4
bytes. All new tables are created with the new date type if you don't use the
--old-protocol option to mysqld.
Error
from table handler: # on some operating systems.
--enable-assembler option to configure,
for x86 machines (tested on Linux + gcc). This will enable
assembler functions for the most important string functions for more speed!
Version 3.21 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
SIGHUP to mysqld;
mysqld core dumped when starting from boot on some systems.
DELETE FROM tbl_name without a WHERE condition
is now done the long way when you use LOCK TABLES or if the table
is in use, to avoid race conditions.
INSERT INTO TABLE (timestamp_column) VALUES (NULL); didn't
set timestamp. mysqladmin
refresh often. This could in some very rare cases corrupt the header of
the index file and cause error 126 or 138.
refresh() when running with the
--skip-locking option. There was a ``very small'' time gap after
a mysqladmin refresh when a table could be corrupted if one
thread updated a table while another thread did mysqladmin
refresh and another thread started a new update ont the same table
before the first thread had finished. A refresh (or
--flush-tables) will now not return until all used tables are
closed!
SELECT DISTINCT with a WHERE clause that didn't
match any rows returned a row in some contexts (bug only in 3.21.31).
GROUP BY + ORDER BY returned one empty row when
no rows where found.
Use_count: Wrong count
for ... in the error log file. TINYINT type on Irix.
LEFT("constant_string",function).
FIND_IN_SET().
LEFT JOIN core dumped if the second table is used with a
constant WHERE/ON expression that uniquely identifies one record.
DATE_FORMAT() and incorrect dates.
DATE_FORMAT() now ignores '%' to make it possible to
extend it more easily in the future. mysql now returns an exit code > 0 if the query returned
an error.
mysql client. By
Tommy Larsen tommy@mix.hive.no.
safe_mysqld to redirect startup messages to
'hostname'.err instead of 'hostname'.log to reclaim
file space on mysqladmin refresh.
ENUM always had the first entry as default value.
ALTER TABLE wrote two entries to the update log.
sql_acc() now closes the mysql grant tables
after a reload to save table space and memory.
LOAD DATA to use less memory with tables and
BLOB columns.
SELECT problem with LEFT() when using the
czech character set.
isamchk; it couldn't repair a packed table
in a very unusual case.
SELECT statements with & or |
(bit functions) failed on columns with NULL values.
LOCK TABLES + DELETE from tbl_name never removed
locks properly.
OR function.
umask() and creating new
databases.
SELECT ... INTO OUTFILE
...
MIN(integer) or
MAX(integer) in GROUP BY.
WEEK("XXXX-xx-01"). Error
from table handler: # on some operating systems. GET_LOCK(string,timeout),
RELEASE_LOCK(string).
Opened_tables to show status.
mysqld through telnet + TCP/IP.
WHERE key_part_1 >=
something AND key_part_2 <= something_else.
configure for detection of FreeBSD 3.0 9803xx and
above
WHERE with string_column_key = constant_string didn't always
find all rows if the column had many values differing only with characters of
the same sort value (like e and 'e).
umask() to make log files non-readable for normal
users.
--old-protocol option to mysqld.
SELECT which matched all key fields returned the values in
the case of the matched values, not of the found values. (Minor problem.)
FROM_DAYS(0) now returns "0000-00-00".
DATE_FORMAT(), PM and AM were swapped for hours 00 and 12.
BLOB/TEXT in GROUP
BY with many tables.
ENUM field that is not declared NOT NULL has
NULL as the default value. (Previously, the default value was the
first enumeration value.)
INDEX (Organisation,Surname(35),Initials(35)).
SELECT ... FROM many_tables much faster.
accept() to possibly fix some
problems on some Linux machines. typedef 'string' to typedef 'my_string'
for better portability.
isamchk. Try isamchk
--help.
filesort()
didn't work. Affects DISTINCT, ORDER BY and
GROUP BY on 64-bit processors. SELECT
on the table.
OR operators on
key parts inside each other.
MIN() and MAX() to work properly with
strings and HAVING.
0664 to
0660.
LEFT JOIN and constant expressions in the
ON part.
configure now works better on OSF1 (tested on 4.0D).
LIKE optimisation with international
character support.
DBI to 0.93. TIME,
DATE, TIMESTAMP, TEXT,
BIT, ENUM, NO, ACTION,
CHECK, YEAR, MONTH, DAY,
HOUR, MINUTE, SECOND,
STATUS, VARIABLES.
TIMESTAMP to NULL in LOAD DATA
INFILE ... didn't set the current time for the TIMESTAMP.
BETWEEN to recognise binary strings. Now
BETWEEN is case sensitive.
--skip-thread-priority option to mysqld,
for systems where mysqld's thread scheduling doesn't work
properly (BSDI 3.1).
DAYNAME() and MONTHNAME().
TIME_FORMAT(). This works like
DATE_FORMAT(), but takes a time string ('HH:MM:DD')
as argument.
ORs of key
parts inside ANDs.
variables to mysqladmin.
ALTER TABLE to work with Windows (Windows can't
rename open files). Also fixed a couple of small bugs in the Windows version.
crash-me and the benchmarks on the
following platforms: SunOS 5.6 sun4u, SunOS 5.5.1 sun4u, SunOS 4.14 sun4c,
SunOS 5.6 i86pc, Irix 6.3 mips5k, HP-UX 10.20 hppa, AIX 4.2.1 ppc, OSF1 V4.0
alpha, FreeBSD 2.2.2 i86pc and BSDI 3.1 i386.
COUNT(*) problems when the WHERE clause
didn't match any records. (Bug from 3.21.17.)
NULL = NULL is true. Now you must use IS
NULL or IS NOT NULL to test whether or not a value is
NULL. (This is according to ANSI SQL but may break old
applications that are ported from mSQL.) You can get the old
behavior by compiling with -DmSQL_COMPLIANT.
LEFT OUTER JOIN
clauses.
ORDER BY on string formula with possible
NULL values.
DAYOFYEAR(), DAYOFMONTH(),
MONTH(), YEAR(), WEEK(),
QUARTER(), HOUR(), MINUTE(),
SECOND() and FIND_IN_SET().
SHOW VARIABLES.
mysql> SELECT 'first ' 'second'; -> 'first second'
mysqlaccess to 2.02.
LIKE.
WHERE data_field = date_field2 AND
date_field2 = constant.
SHOW STATUS.
mysqladmin stat to return the right number of queries.
AUTO_INCREMENT attribute or is a TIMESTAMP. This is
needed for the new Java driver.
configure bugs and increased maximum table
size from 2G to 4G. DBD to 1823. This version implements
mysql_use_result in DBD-Mysql.
REVERSE() (by Zeev Suraski). DBI to 0.91.
LEFT OUTER JOIN.
CROSS JOIN syntax. CROSS is now a reserved
word.
yacc/bison stack allocation to be even
safer and to allow MySQL to handle even bigger expressions.
ORDER BY was slow when used with key ranges. --with-unix-socket-path to
avoid confusion.
LEFT OUTER JOIN.
LEFT,
NATURAL, USING.
MYSQL_HOST as the default host if it's defined.
SELECT col_name, SUM(expr) now returns NULL for
col_name when there are matching rows.
BLOBs with
ASCII characters over 127.
mysqld
restart if one thread was reading data that another thread modified.
LIMIT offset,count didn't work in INSERT ...
SELECT.
POWER(),
SPACE(), COT(), DEGREES(),
RADIANS(), ROUND(2 arg) and TRUNCATE().
LOCATE()
parameters were swapped according to ODBC standard. Fixed.
TIME_TO_SEC().
NOT NULL
fields.
UPDATE SET ...
statements.
BLOB and
TEXT, to be compatible with mysqldump. mysqlperl is
now from Msql-Mysql-modules. This means that connect() now takes
host, database, user,
password arguments! The old version took host,
database, password, user.
DATE '1997-01-01', TIME '12:10:10' and
TIMESTAMP '1997-01-01 12:10:10' formats required by ANSI SQL.
Warning: Incompatible change! This has the unfortunate
side-effect that you no longer can have columns named DATE,
TIME or TIMESTAMP. :( Old columns can still be
accessed through tablename.columnname!)
make programs trying to rebuild it.
readline library upgraded to version 2.1.
DBI/DBD is now included in the
distribution. DBI is now the recommended way to connect to MySQL
from Perl.
DBD, with test results from
mSQL 2.0.3, MySQL, PostgreSQL 6.2.1 and Solid server 2.2.
crash-me is now included with the benchmarks; This is a Perl
program designed to find as many limits as possible in a SQL server. Tested
with mSQL, PostgreSQL, Solid and MySQL.
mysql command line tool,
by Zeev Suraski and Andi Gutmans.
REPLACE that works like INSERT
but replaces conflicting records with the new record. REPLACE INTO TABLE
... SELECT ... works also.
CREATE DATABASE db_name and DROP
DATABASE db_name.
RENAME option to ALTER TABLE: ALTER
TABLE name RENAME TO new_name.
make_binary_distribution now includes `libgcc.a' in
`libmysqlclient.a'. This should make linking work for people who
don't have gcc.
net_write() to my_net_write() because of
a name conflict with Sybase.
DAYOFWEEK() compatible with ODBC.
bison memory overrun checking to make
MySQL safer with weird queries. configure problems on some platforms.
DATE_FORMAT().
NOT IN.
{fn now()
}
DATE and TIME values with
NULL.
FLOAT.
Previously, the values were converted to INTs before sorting.
key_column=constant.
DOUBLE values sorted on integer results
instead.
mysql no longer needs a database argument.
HAVING should be. According to ANSI,
it should be after GROUP BY but before ORDER BY.
MySQL Version 3.20 incorrectly had it last.
USE DATABASE to start using another
database.
mysqld doesn't crash even if you haven't done a
ulimit -n 256 before starting mysqld.
errno. This
makes Linux systems much safer!
SELECT.
LIKE on number key.
--table option to mysql to print in table
format. Moved time and row information after query result. Added automatic
reconnect of lost connections.
!= as a synonym for <>.
VERSION() to make easier logs.
ftruncate() call in MIT-pthreads. This made
isamchk destroy the `.ISM' files on (Free)BSD 2.x
systems.
__P_ patch in MIT-pthreads.
NULL if the returned string should be longer than
max_allowed_packet bytes.
INTERVAL type to ENUM,
because INTERVAL is used in ANSI SQL.
JOIN + GROUP + INTO
OUTFILE, the result wasn't grouped.
LIKE with '_' as last character didn't work.
Fixed.
TRIM() function.
CURTIME().
ENCRYPT() function by Zeev Suraski.
FOREIGN KEY syntax skipping. New reserved words:
MATCH, FULL, PARTIAL.
mysqld now allows IP number and hostname to the
--bind-address option.
SET OPTION CHARACTER SET cp1251_koi8 to enable
conversions of data to/from cp1251_koi8.
CREATE COLUMN syntax of NOT NULL
columns to be after the DEFAULT value, as specified in the ANSI
SQL standard. This will make mysqldump with NOT NULL
and default values incompatible with MySQL Version 3.20.
ALTER TABLE tbl_name ALTER COLUMN col_name SET
DEFAULT NULL.
CHAR and BIT as synonyms for
CHAR(1).
INSERT ... SELECT ... GROUP BY didn't work in some cases. An
Invalid use of group function error occurred.
LIMIT, SELECT now always uses keys
instead of record scan. This will give better performance on
SELECT and a WHERE that matches many rows.
BIT_OR() and
BIT_AND().
CHECK and
REFERENCES. CHECK is now a reserved word.
ALL option to GRANT for better
compatibility. (GRANT is still a dummy function.)
ORDER BY and GROUP BY with
NULL columns.
last_insert_id() to retrieve last
AUTO_INCREMENT value. This is intended for clients to ODBC that
can't use the mysql_insert_id() API function, but can be used by
any client.
--flush-logs option to mysqladmin.
STATUS to mysql.
ORDER BY/GROUP BY because of
bug in gcc.
INSERT ... SELECT ... GROUP BY. mysqlaccess.
CREATE now supports all ODBC types and the mSQL
TEXT type. All ODBC 2.5 functions are also supported (added
REPEAT). This provides better portability.
TINYTEXT, TEXT,
MEDIUMTEXT and LONGTEXT. These are actually
BLOBtypes, but all searching is done in case-insensitive fashion.
BLOB fields are now TEXT fields. This
only changes that all searching on strings is done in case-sensitive fashion.
You must do an ALTER TABLE and change the field type to
BLOB if you want to have tests done in case-sensitive fashion.
configure issues.
test-select works. --enable-unix-socket=pathname option to
configure.
SUM() functions. For
example, you can now use SUM(column)/COUNT(column).
PI(),
ACOS(), ASIN(), ATAN(),
COS(), SIN() and TAN().
net_print() in
`procedure.cc'.
SELECT ... INTO OUTFILE syntax.
GROUP BY and SELECT on key with
many values.
mysql_fetch_lengths() sometimes returned incorrect lengths
when you used mysql_use_result(). This affected at least some
cases of mysqldump --quick.
WHERE const op field.
NULL fields.
--pid-file=# option to mysqld.
FROM_UNIXTIME(), originally by Zeev
Suraski.
BETWEEN in range optimiser (did only test = of
the first argument).
mysql_errno(), to get the error
number of the error message. This makes error checking in the client much
easier. This makes the new server incompatible with the 3.20.x server when
running without --old-protocol. The client code is backward
compatible. More information can be found in the `README' file!
sigwait and
sigset defines).
configure should now be able to detect the last argument to
accept(). -O tmp_table_size=# to mysqld.
FROM_UNIXTIME(timestamp) which returns a date
string in 'YYYY-MM-DD HH:MM:DD' format.
SEC_TO_TIME(seconds) which returns a string in
'HH:MM:SS' format.
SUBSTRING_INDEX(), originally by Zeev Suraski.
mysqld doesn't work on it yet.
pthread_create to work. mysqld doesn't accept hostnames that start with digits
followed by a '.', because the hostname may look like an IP
number.
--skip-networking option to mysqld, to
only allow socket connections. (This will not work with MIT-pthreads!)
free() that killed the server on
CREATE DATABASE or DROP DATABASE.
mysqld -O options to better names.
-O join_cache_size=# option to mysqld.
-O max_join_size=# option to mysqld, to be
able to set a limit how big queries (in this case big = slow) one should be
able to handle without specifying SET OPTION SQL_BIG_SELECTS=1. A
# = is about 10 examined records. The default is ``unlimited''.
TIME, DATE,
DATETIME or TIMESTAMP column to a constant, the
constant is converted to a time value before performing the comparison. This
will make it easier to get ODBC (particularly Access97) to work with the above
types. It should also make dates easier to use and the comparisons should be
quicker than before.
query() in
mysqlperl to take a query with \0 in it.
YYMMDD) didn't work.
UPDATE clause.
SELECT * INTO OUTFILE, which didn't correctly if the outfile
already existed.
mysql now shows the thread ID when starting or doing a
reconnect.
--new, but it crashes core a lot yet...
isam library should be relatively 64-bit clean.
isamchk which can detect and fix more problems.
isamlog.
mysqladmin: you can now do mysqladmin kill
5,6,7,8 to kill multiple threads.
-O backlog=# option to mysqld.
ALTER TABLE now returns warnings from field conversions.
ASCII().
BETWEEN(a,b,c). Use the standard ANSI syntax
instead: expr BETWEEN expr AND expr.
SUM() functions.
tbl_name.field_name in
UPDATE.
SELECT DISTINCT when using 'hidden group'. For example:
mysql> SELECT DISTINCT MOD(some_field,10) FROM test
GROUP BY some_field;
Note: some_field is normally in the SELECT
part. ANSI SQL should require it. INTERVAL, EXPLAIN,
READ, WRITE, BINARY.
CHAR(num,...).
IN. This uses a binary search to find a match.
LOCK TABLES tbl_name [AS alias] {READ|WRITE} ...
--log-update option to mysqld, to get a
log suitable for incremental updates.
EXPLAIN SELECT ... to get information about how
the optimiser will do the join.
FIELD_TYPE_TINY_BLOB, FIELD_TYPE_MEDIUM_BLOB,
FIELD_TYPE_LONG_BLOB or FIELD_TYPE_VAR_STRING (as
previously returned by mysql_list_fields). You should instead
only use FIELD_TYPE_BLOB or FIELD_TYPE_STRING. If
you want exact types, you should use the command SHOW FIELDS.
0x###### which can be used as a
string (default) or a number.
FIELD_TYPE_CHAR is renamed to FIELD_TYPE_TINY.
DEFAULT values no longer need to be NOT
NULL.
ENUM
SET
double or
long long. This will provide the full 64-bit range with bit
functions and fix some conversions that previously could result in precision
losses. One should avoid using unsigned long long columns with
full 64-bit range (numbers bigger than 9223372036854775807) because
calculations are done with signed long long.
ORDER BY will now put NULL field values first.
GROUP BY will also work with NULL values.
WHERE with expressions.
mysql> SELECT * FROM tbl_name
WHERE key_part_1="customer"
AND key_part_2>=10 AND key_part_2<=10;
Version 3.20 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
Changes from 3.20.18 to 3.20.32b are not documented here because the 3.21 release branched here. And the relevant changes are also documented as changes to the 3.21 version.
-p# (remove # directories from path) to
isamlog. All files are written with a relative path from the
database directory Now mysqld shouldn't crash on shutdown when
using the --log-isam option.
mysqlperl version. It is now compatible with
msqlperl-0.63.
DBD module available at http://mysql.com/Downloads/Contrib/
site.
STD() (standard deviation).
mysqld server is now compiled by default without
debugging information. This will make the daemon smaller and faster.
--basedir option to
mysqld. All other paths are relative in a normal installation.
BLOB columns sometimes contained garbage when used with a
SELECT on more than one table and ORDER BY.
GROUP BY work as
expected (ANSI SQL extension). Example: mysql> SELECT id,id+1 FROM table GROUP BY id;
MYSQL_PWD was reversed. Now
MYSQL_PWD is enabled as default in the default release.
mysqld to core dump with
Arithmetic error on Sparc-386.
--unbuffered option to mysql, for new
mysqlaccess.
BLOB columns and the functions IS
NULL and IS NOT NULL in the WHERE clause.
max_allowed_packet is now 64K for
the server and 512K for the client. This is mainly used to catch incorrect
packets that could trash all memory. The server limit may be changed when it
is started.
safe_mysqld to check for running daemon.
ELT() function is renamed to FIELD(). The
new ELT() function returns a value based on an index:
FIELD() is the inverse of ELT() Example:
ELT(2,"A","B","C") returns "B".
FIELD("B","A","B","C") returns 2.
COUNT(field), where field could have a
NULL value, now works.
SELECT ... GROUP BY.
WHERE with many unoptimisable
brace levels.
get_hostname, only the IP is
checked. Previously, you got Access denied.
INSERT INTO ... SELECT ... WHERE could give the error
Duplicated field.
safe_mysqld to make it ``safer''.
LIKE was case sensitive in some places and case insensitive
in others. Now LIKE is always case insensitive.
'#' anywhere on the line.
SET OPTION SQL_SELECT_LIMIT=#. See the FAQ for
more details.
mysqlaccess script.
FROM_DAYS() and WEEKDAY() to also take a
full TIMESTAMP or DATETIME as argument. Before they
only took a number of type YYYYMMDD or YYMMDD.
UNIX_TIMESTAMP(timestamp_column). mysqld to work around a bug in MIT-pthreads. This
makes multiple small SELECT operations 20 times faster. Now
lock_test.pl should work.
mysql_FetchHash(handle) to mysqlperl.
mysqlbug script is now distributed built to allow for
reporting bugs that appear during the build with it.
getpwuid() instead of
cuserid().
SELECT optimiser when using many tables with the
same column used as key to different tables.
GRANT command to satisfy
Powerbuilder. packets out of order when using MIT-pthreads.
fcntl() fails. Thanks to Mike Bretz for finding this bug.
termbits from `mysql.cc'. This
conflicted with glibc 2.0.
SELECT as superuser without a
database.
SELECT with group calculation to
outfile. -p or --password option to
mysql without an argument, the user is solicited for the password
from the tty.
MYSQL_PWD (by Elmar Haneke).
kill to mysqladmin to kill a
specific MySQL thread.
AUTO_INCREMENT key with
ALTER_TABLE.
AVG() gave too small value on some SELECTs with
GROUP BY and ORDER BY.
DATETIME type (by Giovanni Maruzzelli maruzz@matrice.it).
DONT_USE_DEFAULT_FIELDS works.
CREATE INDEX.
DATE, TIME
and TIMESTAMP.
OR of multiple tables (gave empty set).
DATE and TIME types.
SELECT with AND-OR
levels.
LIMIT and ORDER BY.
ORDER BY and GROUP BY on items that aren't
in the SELECT list. (Thanks to Wim Bonis bonis@kiss.de, for pointing this out.)
INSERT.
SELECT ... WHERE ... = NULL.
glibc 2.0. To get glibc to
work, you should add the `gibc-2.0-sigwait-patch' before compiling
glibc.
ALTER TABLE when changing a NOT
NULL field to allow NULL values.
CREATE TABLE.
CREATE TABLE now allows FLOAT(4) and
FLOAT(8) to mean FLOAT and DOUBLE.
mysqlaccess by Yves.Carlier@rug.ac.be. This program
shows the access rights for a specific user and the grant rows that determine
this grant.
WHERE const op field (by bonis@kiss.de). SELECT ... INTO OUTFILE, all temporary tables are
ISAM instead of HEAP to allow big dumps.
ALTER TABLE according to SQL92.
--port and --socket options to all utility
programs and mysqld.
readdir_r(). Now mysqladmin create
database and mysqladmin drop database should work.
tempnam(). This should fix
the ``sort aborted'' bug.
sql_update. This fixed slow
updates on first connection. (Thanks to Vaclav Bittner for the test.) INSERT INTO ... SELECT ...
MEDIUMBLOB fixed.
ALTER TABLE and BLOBs.
SELECT ... INTO OUTFILE now creates the file in the current
database directory.
DROP TABLE now can take a list of tables.
DESCRIBE (DESC).
make_binary_distribution.
configure's C++ link test.
--without-perl option to configure.
ALTER TABLE didn't copy null bit. As a result, fields that
were allowed to have NULL values were always NULL.
CREATE didn't take numbers as DEFAULT.
ALTER TABLE and multi-part keys. ALTER TABLE, SELECT ... INTO
OUTFILE and LOAD DATA INFILE.
NOW().
mysql/user
table.
add_file_priv which adds the new field
file_priv to the user table. This script must be
executed if you want to use the new SELECT ... INTO and
LOAD DATA INFILE ... commands with a version of MySQL earlier
than 3.20.7.
lock_test.pl test fail.
status to mysqladmin for short
logging.
-k option to mysqlshow, to get key
information for a table.
mysqldump. configure cannot find a -lpthreads
library.
program --help.
RAND([init]).
sql_lex to handle \0 unquoted, but the
client can't send the query through the C API, because it takes a str pointer.
You must use mysql_real_query() to send the query.
mysql_get_client_info().
mysqld now uses the N_MAX_KEY_LENGTH from
`nisam.h' as the maximum allowed key length.
mysql> SELECT filter_nr,filter_nr FROM filter ORDER BY filter_nr;Previously, this resulted in the error:
Column: 'filter_nr' in
order clause is ambiguous.
mysql now outputs '\0', '\t',
'\n' and '\\' when encountering ASCII 0, tab,
newline or '\' while writing tab-separated output. This is to
allow printing of binary data in a portable format. To get the old behavior,
use -r (or --raw).
mysql_fetch_lengths(MYSQL_RES *),
which returns an array of column lengths (of type uint).
IS NULL in WHERE clause.
SELECT option STRAIGHT_JOIN to tell the
optimiser that it should join tables in the given order.
'--' in
`mysql.cc' (Postgres syntax).
SELECT expressions and table columns in a
SELECT which are not used in the group part. This makes it
efficient to implement lookups. The column that is used should be a constant
for each group because the value is calculated only once for the first row
that is found for a group. mysql> SELECT id,lookup.text,sum(*) FROM test,lookup
WHERE test.id=lookup.id GROUP BY id;
SUM(function) (could cause a core dump).
AUTO_INCREMENT placement in the SQL query: INSERT into table (auto_field) values (0);inserted 0, but it should insert an
AUTO_INCREMENT value.
mysql now allows doubled '' or ""
within strings for embedded ' or ".
EXP(), LOG(),
SQRT(), ROUND(), CEILING(). configure source now compiles a thread-free client
library -lmysqlclient. This is the only library that needs to be
linked with client applications. When using the binary releases, you must link
with -lmysql -lmysys -ldbug -lstrings as before.
readline library from bash-2.0.
configure and makefiles (and related
source).
VPATH. Tested with GNU Make 3.75.
safe_mysqld and mysql.server changed to be more
compatible between the source and the binary releases.
LIMIT now takes one or two numeric arguments. If one argument
is given, it indicates the maximum number of rows in a result. If two
arguments are given, the first argument indicates the offset of the first row
to return, the second is the maximum number of rows. With this it's easy to do
a poor man's next page/previous page WWW application.
FIELDS() to ELT().
Changed SQL function INTERVALL() to INTERVAL().
SHOW COLUMNS a synonym for SHOW FIELDS.
Added compatibility syntax FRIEND KEY to CREATE
TABLE. In MySQL, this creates a non-unique key on the given columns.
CREATE INDEX and DROP INDEX as
compatibility functions. In MySQL, CREATE INDEX only checks if
the index exists and issues an error if it doesn't exist. DROP
INDEX always succeeds.
sql_acl (core on new connection).
host, user and db tables
from database test in the distribution.
FIELD_TYPE_CHAR can now be signed (-128 - 127) or unsigned (0
- 255) Previously, it was always unsigned.
CONCAT() and WEEKDAY().
mysqld to be compiled with
SunPro compiler.
'(' immediately after the
function name (no intervening space). For example, 'user(' is
regarded as beginning a function call, and 'user (' is regarded
as an identifier user followed by a '(', not as a
function call. configure and Automake.
It will make porting much easier. The readline library is
included in the distribution.
DBD will follow when the new
DBD code is ported.
mysqld can now be started with
Swedish or English (default) error messages.
INSERT(), RTRIM(),
LTRIM() and FORMAT().
mysqldump now works correctly for all field types (even
AUTO_INCREMENT). The format for SHOW FIELDS FROM
tbl_name is changed so the Type column contains
information suitable for CREATE TABLE. In previous releases, some
CREATE TABLE information had to be patched when re-creating
tables.
BLOB and
TIMESTAMP) are corrected. TIMESTAMP now returns
different date information depending on its create length.
'_'.
Version 3.19 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
DATABASE(), USER(),
POW(), LOG10() (needed for ODBC).
WHERE with an ORDER BY on fields from only
one table, the table is now preferred as first table in a multi-join.
HAVING and IS NULL or IS NOT NULL
now works.
SUM(),
AVG()...) didn't work together. Fixed.
mysqldump: Didn't send password to server. 'Locked' to process list as info if a query
is locked by another query.
IF(arg,syntax_error,syntax_error) crashed.
CEILING(), ROUND(),
EXP(), LOG() and SQRT().
BETWEEN to handle strings. SELECT with grouping on BLOB columns not
to return incorrect BLOB info. Grouping, sorting and distinct on
BLOB columns will not yet work as expected (probably it will
group/sort by the first 7 characters in the BLOB). Grouping on
formulas with a fixed string size (use MID() on a
BLOB) should work.
BLOB fields, the BLOB was garbage on output.
DISTINCT with calculated columns. This appendix will help you port MySQL to other operationg systems. Do check the list of currently supported operating systems first. See section 2.2.2 Operating Systems Supported by MySQL. If you have created a new port of MySQL, please let us know so that we can list it here and on our web site (http://mysql.com/), recommending it to other users.
Note: If you create a new port of MySQL, you are free to copy and distribute it under the GPL license, but it does not make you a copyright holder of MySQL.
A working Posix thread library is needed for the server. On Solaris 2.5 we use Sun PThreads (the native thread support in 2.4 and earlier versions are not good enough) and on Linux we use LinuxThreads by Xavier Leroy, Xavier.Leroy@inria.fr.
The hard part of porting to a new Unix variant without good native thread support is probably to port MIT-pthreads. See `mit-pthreads/README' and Programming POSIX Threads (http://www.humanfactor.com/pthreads/).
The MySQL distribution includes a patched version of Provenzano's Pthreads from MIT (see the MIT Pthreads web page at http://www.mit.edu:8001/people/proven/pthreads.html). This can be used for some operating systems that do not have POSIX threads.
It is also possible to use another user level thread package named FSU Pthreads (see FSU Pthreads home page). This implementation is being used for the SCO port.
See the `thr_lock.c' and `thr_alarm.c' programs in the `mysys' directory for some tests/examples of these problems.
Both the server and the client need a working C++ compiler (we use
gcc and have tried SparcWorks). Another compiler that is known to
work is the Irix cc.
To compile only the client use ./configure --without-server.
There is currently no support for only compiling the server, nor is it likly to be added unless someone has a good reason for it.
If you want/need to change any `Makefile' or the configure script
you must get Automake and Autoconf. We have used the automake-1.2
and autoconf-2.12 distributions.
All steps needed to remake everything from the most basic files.
/bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug=full --prefix='your installation directory' # The makefiles generated above need GNU make 3.75 or newer. # (called gmake below) gmake clean all install init-db
If you run into problems with a new port, you may have to do some debugging of MySQL! See section E.1 Debugging a MySQL server.
NOTE: Before you start debugging mysqld, first
get the test programs mysys/thr_alarm and
mysys/thr_lock to work. This will ensure that your thread
installation has even a remote chance to work!
If you are using some functionality that is very new in MySQL, you can try to
run mysqld with the --skip-new (which will disable all
new, potentially unsafe functionality) or with --safe-mode which
disables a lot of optimisation that may cause problems. See section A.4.1 What
To Do If MySQL Keeps Crashing.
If mysqld doesn't want to start, you should check that you don't
have any my.cnf files that interfere with your setup! You can check
your my.cnf arguments with mysqld --print-defaults and
avoid using them by starting with mysqld --no-defaults ....
If mysqld starts to eat up CPU or memory or if it ``hangs'', you
can use mysqladmin processlist status to find out if someone is
executing a query that takes a long time. It may be a good idea to run
mysqladmin -i10 processlist status in some window if you are
experiencing performance problems or problems when new clients can't connect.
The command mysqladmin debug will dump some information about
locks in use, used memory and query usage to the mysql log file. This may help
solve some problems. This command also provides some useful information even if
you haven't compiled MySQL for debugging!
If the problem is that some tables are getting slower and slower you should
try to optimise the table with OPTIMIZE TABLE or
myisamchk. See section 4
MySQL Database Administration. You should also check the slow queries with
EXPLAIN.
You should also read the OS-specific section in this manual for problems that may be unique to your environment. See section 2.6 Operating System Specific Notes.
If you have some very specific problem, you can always try to debug MySQL. To
do this you must configure MySQL with the --with-debug or the
--with-debug=full option. You can check whether or not MySQL was
compiled with debugging by doing: mysqld --help. If the
--debug flag is listed with the options then you have debugging
enabled. mysqladmin ver also lists the mysqld version
as mysql ... --debug in this case.
If you are using gcc or egcs, the recommended configure line is:
CC=gcc CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-debug --with-extra-charsets=complex
This will avoid problems with the libstdc++ library and with C++
exceptions (many compilers have problems with C++ exceptions in threaded code)
and compile a MySQL version with support for all character sets.
If you suspect a memory overrun error, you can configure MySQL with
--with-debug=full, which will install a memory allocation
(SAFEMALLOC) checker. Running with SAFEMALLOC is
however quite slow, so if you get performance problems you should start
mysqld with the --skip-safemalloc option. This will
disable the memory overrun checks for each call to malloc and
free.
If mysqld stops crashing when you compile it with
--with-debug, you have probably found a compiler bug or a timing
bug within MySQL. In this case you can try to add -g to the
CFLAGS and CXXFLAGS variables above and not use
--with-debug. If mysqld now dies, you can at least
attach to it with gdb or use gdb on the core file to
find out what happened.
When you configure MySQL for debugging you automatically enable a lot of
extra safety check functions that monitor the health of mysqld. If
they find something ``unexpected,'' an entry will be written to
stderr, which safe_mysqld directs to the error log!
This also means that if you are having some unexpected problems with MySQL and
are using a source distribution, the first thing you should do is to configure
MySQL for debugging! (The second thing, of course, is to send mail to mysql@lists.mysql.com and ask for help.
Please use the mysqlbug script for all bug reports or questions
regarding the MySQL version you are using!
In the Windows MySQL distribution, mysqld.exe is by default
compiled with support for trace files.
If the mysqld server doesn't start or if you can cause the
mysqld server to crash quickly, you can try to create a trace file
to find the problem.
To do this you have to have a mysqld that is compiled for
debugging. You can check this by executing mysqld -V. If the
version number ends with -debug, it's compiled with support for
trace files.
Start the mysqld server with a trace log in
`/tmp/mysqld.trace' (or `C:\mysqld.trace' on Windows):
mysqld --debug
On Windows you should also use the --standalone flag to not
start mysqld as a service:
In a DOS window do:
mysqld --debug --standalone
After this you can use the mysql.exe command line tool in a
second DOS window to reproduce the problem. You can take down the above
mysqld server with mysqladmin shutdown.
Note that the trace file will get very big! If you want to have a smaller trace file, you can use something like:
mysqld
--debug=d,info,error,query,general,where:O,/tmp/mysqld.trace
which only prints information with the most interesting tags in `/tmp/mysqld.trace'.
If you make a bug report about this, please only send the lines from the trace file to the appropriate mailing list where something seems to go wrong! If you can't locate the wrong place, you can ftp the trace file, together with a full bug report, to ftp://support.mysql.com/pub/mysql/secret/ so that a MySQL developer can take a look a this.
The trace file is made with the DBUG package by Fred Fish. See section E.3 The DBUG package..
On most system you can also start mysqld from gdb
to get more information if mysqld crashes.
With some older gdb versions on Linux you must use run
--one-thread if you want to be able to debug mysqld threads.
In this case you can only have one thread active at a time. We recommend you to
upgrade to gdb 5.1 ASAP as thread debugging works much better with this version!
When running mysqld under gdb, you should disable the stack
trace with --skip-stack-trace to be able to catch segfaults within
gdb.
It's very hard to debug MySQL under gdb if you do a lot of new
connections the whole time as gdb doesn't free the memory for old
threads. You can avoid this problem by starting mysqld with
-O thread_cache_size= 'max_connections +1'. In most cases just
using -O thread_cache_size=5' will help a lot!
If you want to get a core dump on Linux if mysqld dies with a
SIGSEGV signal, you can start mysqld with the
--core-file option. This core file can be used to make a backtrace
that may help you find out why mysqld died:
shell> gdb mysqld core gdb> backtrace full gdb> exit
See section A.4.1 What To Do If MySQL Keeps Crashing.
If you are using gdb 4.17.x or above on Linux, you should install a `.gdb' file, with the following information, in your current directory:
set print sevenbit off handle SIGUSR1 nostop noprint handle SIGUSR2 nostop noprint handle SIGWAITING nostop noprint handle SIGLWP nostop noprint handle SIGPIPE nostop handle SIGALRM nostop handle SIGHUP nostop handle SIGTERM nostop noprint
If you have problems debugging threads with gdb, you should download gdb 5.x and try this instead. The new gdb version has very improved thread handling!
Here is an example how to debug mysqld:
shell> gdb /usr/local/libexec/mysqld gdb> run ... backtrace full # Do this when mysqld crashes
Include the above output in a mail generated with mysqlbug and
mail this to mysql@lists.mysql.com.
If mysqld hangs you can try to use some system tools like
strace or /usr/proc/bin/pstack to examine where
mysqld has hung.
strace /tmp/log libexec/mysqld
If you are using the Perl DBI interface, you can
turn on debugging information by using the trace method or by
setting the DBI_TRACE environment variable. See section 8.2.2
The DBI Interface.
On some operating systems, the error log will contain a stack trace if
mysqld dies unexpectedly. You can use this to find out where (and
maybe why) mysqld died. See section 4.9.1 The
Error Log. To get a stack trace, you must not compile mysqld
with the -fomit-frame-pointer option to gcc. See section E.1.1
Compiling MYSQL for debugging.
If the error file contains something like the following:
mysqld got signal 11; The manual section 'Debugging a MySQL server' tells you how to use a stack trace and/or the core file to produce a readable backtrace that may help in finding out why mysqld died Attemping backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong stack range sanity check, ok, backtrace follows 0x40077552 0x81281a0 0x8128f47 0x8127be0 0x8127995 0x8104947 0x80ff28f 0x810131b 0x80ee4bc 0x80c3c91 0x80c6b43 0x80c1fd9 0x80c1686
you can find where mysqld died by doing the following:
mysqld server: nm -n libexec/mysqld > /tmp/mysqld.symNote that many MySQL binary distributions comes with the above file, named
mysqld.sym.gz. In this case you must unpack this by doing: gunzip < bin/mysqld.sym.gz > /tmp/mysqld.sym
resolve_stack_dump -s /tmp/mysqld.sym -n
mysqld.stack. This will print out where mysqld died. If
this doesn't help you find out why mysqld died, you should make a
bug report and include the output from the above commend with the bug report.
Note however that in most cases it will not help us to just have a stack trace
to find the reason for the problem. To be able to locate the bug or provide a
workaround, we would in most cases need to know the query that killed
mysqld and preferable a test case so that we can repeat the
problem! See section 1.6.2.3
How to Report Bugs or Problems. Note that before starting mysqld with --log you
should check all your tables with myisamchk. See section 4
MySQL Database Administration.
If mysqld dies or hangs, you should start mysqld
with --log. When mysqld dies again, you can examine
the end of the log file for the query that killed mysqld.
If you are using --log without a file name, the log is stored in
the database directory as 'hostname'.log In most cases it's the last query in
the log file that killed mysqld, but if possible you should verify
this by restarting mysqld and executing the found query from the
mysql command line tools. If this works, you should also test all
complicated queries that didn't complete.
You can also try the command EXPLAIN on all SELECT
statements that takes a long time to ensure that mysqld is using
indexes properly. See section 5.2.1
EXPLAIN Syntax (Get Information About a SELECT).
You can find the queries that take a long time to execute by starting
mysqld with --log-slow-queries. See section 4.9.5
The Slow Query Log.
If you find the text mysqld restarted in the error log file
(normally named `hostname.err') you have probably found a query that
causes mysqld to fail. If this happens you should check all your
tables with myisamchk (see section 4
MySQL Database Administration), and test the queries in the MySQL log files
to see if one doesn't work. If you find such a query, try first upgrading to the
newest MySQL version. If this doesn't help and you can't find anything in the
mysql mail archive, you should report the bug to mysql@lists.mysql.com. Links to mail
archives are available online at http://lists.mysql.com/.
If you have started mysqld with myisam-recover,
MySQL will automatically check and try to repair MyISAM tables if
they are marked as 'not closed properly' or 'crashed'. If this happens, MySQL
will write an entry in the hostname.err file 'Warning:
Checking table ...' which is followed by Warning: Repairing
table if the table needs to be repaired. If you get a lot of these
errors, without mysqld having died unexpectedly just before, then
something is wrong and needs to be investigated further. See section 4.1.1
mysqld Command-line Options.
It's of course not a good sign if mysqld did died unexpectedly,
but in this case one shouldn't investigate the Checking table...
messages but instead try to find out why mysqld died.
If you get corrupted tables or if mysqld always fails after some
update commands, you can test if this bug is reproducible by doing the
following:
mysqladmin shutdown).
myisamchk -s database/*.MYI. Repair any
wrong tables with myisamchk -r database/table.MYI.
mysqld with --log-bin. See section 4.9.4
The Binary Update Log. If you want to find a query that crashes
mysqld, you should use --log --log-bin.
mysqld server.
mysqld server without
--log-bin
mysqlbinlog update-log-file |
mysql. The update log is saved in the MySQL database directory with the
name hostname-bin.#.
mysqld to
die with the above command, you have found reproducible bug that should be
easy to fix! FTP the tables and the binary log to ftp://support.mysql.com/pub/mysql/secret/
and send a mail to bugs@lists.mysql.com or (if you are a
support customer) to support@mysql.com
about the problem and the MySQL team will fix it as soon as possible. You can also use the script mysql_find_rows to just execute some
of the update statements if you want to narrow down the problem.
To be able to debug a MySQL client with the integrated debug package, you
should configure MySQL with --with-debug or
--with-debug=full. See section 2.3.3
Typical configure Options.
Before running a client, you should
set the MYSQL_DEBUG environment variable:
shell> MYSQL_DEBUG=d:t:O,/tmp/client.trace shell> export MYSQL_DEBUG
This causes clients to generate a trace file in `/tmp/client.trace'.
If you have problems with your own client code, you should attempt to connect
to the server and run your query using a client that is known to work. Do this
by running mysql in debugging mode (assuming you have compiled
MySQL with debugging on):
shell> mysql --debug=d:t:O,/tmp/client.trace
This will provide useful information in case you mail a bug report. See section 1.6.2.3 How to Report Bugs or Problems.
If your client crashes at some 'legal' looking code, you should check that your `mysql.h' include file matches your mysql library file. A very common mistake is to use an old `mysql.h' file from an old MySQL installation with new MySQL library.
The MySQL server and most MySQL clients are compiled with the DBUG package originally made by Fred Fish. When one has configured MySQL for debugging, this package makes it possible to get a trace file of what the program is debugging. See section E.1.2 Creating trace files.
One uses the debug package by invoking the program with the
--debug="..." or the -#... option.
Most MySQL programs has a default debug string that will be used if you don't
specify an option to --debug. The default trace file is usually
/tmp/programname.trace on Unix and \programname.trace
on Windows.
The debug control string is a sequence of colon separated fields as follows:
<field_1>:<field_2>:...:<field_N>
Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:
flag[,modifier,modifier,...,modifier]
The currently recognised flag characters are:
| Flag | Description |
| d | Enable output from DBUG_<N> macros for the current state. May be followed by a list of keywords which selects output only for the DBUG macros with that keyword. An empty list of keywords implies output for all macros. |
| D | Delay after each debugger output line. The argument is the number of
tenths of seconds to delay, subject to machine capabilities. That is,
-#D,20 is delay two seconds. |
| f | Limit debugging and/or tracing, and profiling to the list of named functions. Note that a null list will disable all functions. The appropriate "d" or "t" flags must still be given, this flag only limits their actions if they are enabled. |
| F | Identify the source file name for each line of debug or trace output. |
| i | Identify the process with the pid or thread id for each line of debug or trace output. |
| g | Enable profiling. Create a file called 'dbugmon.out' containing information that can be used to profile the program. May be followed by a list of keywords that select profiling only for the functions in that list. A null list implies that all functions are considered. |
| L | Identify the source file line number for each line of debug or trace output. |
| n | Print the current function nesting depth for each line of debug or trace output. |
| N | Number each line of dbug output. |
| o | Redirect the debugger output stream to the specified file. The default output is stderr. |
| O | As O but the file is really flushed between each write.
When needed the file is closed and reopened between each write. |
| p | Limit debugger actions to specified processes. A process must be identified with the DBUG_PROCESS macro and match one in the list for debugger actions to occur. |
| P | Print the current process name for each line of debug or trace output. |
| r | When pushing a new state, do not inherit the previous state's function nesting level. Useful when the output is to start at the left margin. |
| S | Do function _sanity(_file_,_line_) at each debugged function until _sanity() returns something that differs from 0. (Mostly used with safemalloc to find memory leaks) |
| t | Enable function call/exit trace lines. May be followed by a list (containing only one modifier) giving a numeric maximum trace level, beyond which no output will occur for either debugging or tracing macros. The default is a compile time option. |
Some examples of debug control strings which might appear on a shell command line (the "-#" is typically used to introduce a control string to an application program) are:
-#d:t -#d:f,main,subr1:F:L:t,20 -#d,input,output,files:n -#d:t:i:O,\\mysqld.trace
In MySQL, common tags to print (with the d option) are:
enter,exit,error,warning,info
and loop.
Currently MySQL only supports table locking for
ISAM/MyISAM and HEAP tables and page
level locking for BDB tables. See section 5.3.1
How MySQL Locks Tables. With MyISAM tables one can freely mix
INSERT and SELECT without locks
(Versioning).
Starting in version 3.23.33, you can analyse the table lock contention on
your system by checking Table_locks_waited and
Table_locks_immediate environment variables.
Some database users claim that MySQL cannot support near the number of concurrent users because it lacks row-level locking. This may be true for some specific applications, but is not generally true. As always this depends totally on what the application does and what is the access/update pattern of the data.
Pros for row locking:
Cons:
GROUP
BY on a large part of the data or if one has to often scan the whole
table.
Table locks are superior to page level / row level locks in the following cases:
UPDATE table_name SET column=value WHERE unique_key# DELETE FROM table_name WHERE unique_key=#
SELECT combined with INSERT (and very few
UPDATE's and DELETE's.
GROUP BY on the whole table without any writers.
Other options than row / page level locking:
Versioning (like we use in MySQL for concurrent inserts) where you can have one writer at the same time as many readers. This means that the database/table supports different views for the data depending on when one started to access it. Other names for this are time travel, copy on write or copy on demand.
Copy on demand is in many case much better than page or row level locking; The worst case does, however, use much more memory than when using normal locks.
Instead of using row level locks one can use application level locks (like get_lock/release_lock in MySQL). This works of course only in well-behaved applications.
In many cases one can do an educated guess which locking type is best for the application but generally it's very hard to say that a given lock type is better than another; Everything depends on the application and different part of the application may require different lock types.
Here are some tips about locking in MySQL:
On web application most applications do lots of selects, very few deletes, updates mainly on keys and inserts in some specific tables. The base MySQL setup is very well tuned for this.
Concurrent users is not a problem if one doesn't mix updates and selects that needs to examine many rows in the same table.
If one mixes inserts and deletes on the same table then INSERT
DELAYED may be of great help.
One can also use LOCK TABLES to speed up things (many updates
within a single lock is much faster than updates without locks). Splitting thing
to different tables will also helps.
If you get speed problems with the table locks in MySQL, you may be able to
solve these to convert some of your tables to BDB tables. See
section 7.6
BDB or Berkeley_DB Tables.
The optimisation section in the manual covers a lot of different aspects of how to tune ones application. See section 5.2.11 Other Optimisation Tips.
I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:
They use an old version of a lot of POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification.
Some wrappers are already written. See `mysys/my_pthread.c' for more info.
At least the following should be changed:
pthread_get_specific should use one argument.
sigwait should take two arguments. A lot of functions (at least
pthread_cond_wait, pthread_cond_timedwait) should
return the error code on error. Now they return -1 and set errno.
Another problem is that user-level threads use the ALRM signal
and this aborts a lot of functions (read, write,
open...). MySQL should do a retry on interrupt on all of these but
it is not that easy to verify it.
The biggest unsolved problem is the following:
To get thread-level alarms I changed `mysys/thr_alarm.c' to wait
between alarms with pthread_cond_timedwait(), but this aborts with
error EINTR. I tried to debug the thread library as to why this
happens, but couldn't find any easy solution.
If someone wants to try MySQL with RTS threads I suggest the following:
-DHAVE_rts_threads.
thr_alarm.
thr_alarm. If it runs without any ``warning'', ``error''
or aborted messages, you are on the right track. Here is a successful run on
Solaris: Main thread: 1 Thread 0 (5) started Thread: 5 Waiting process_alarm Thread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end
MySQL is very dependent on the thread package used. So when choosing a good platform for MySQL, the thread package is very important.
There are at least three types of thread packages:
ps may show the different threads. If one thread aborts,
the whole process aborts. Most system calls are thread safe and should require
very little overhead. Solaris, HP-UX, AIX and OSF1 have kernel threads.
In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn't really ``thread aware''.
Here is a list of all the environment variables that are used directly or indirectly by MySQL. Most of these can also be found in other places in this manual.
Note that any options on the command line will take precedence over values specified in configuration files and environment variables, and values in configuration files take precedence over values in environment variables.
In many cases it's preferable to use a configure file instead of environment variables to modify the behavior of MySQL. See section 4.1.2 my.cnf Option Files.
| Variable | Description |
CCX |
Set this to your C++ compiler when running configure. |
CC |
Set this to your C compiler when running configure. |
CFLAGS |
Flags for your C compiler when running configure. |
CXXFLAGS |
Flags for your C++ compiler when running configure. |
DBI_USER |
The default user name for Perl DBI. |
DBI_TRACE |
Used when tracing Perl DBI. |
HOME |
The default path for the mysql history file is
`$HOME/.mysql_history'. |
LD_RUN_PATH |
Used to specify where your libmysqlclient.so is. |
MYSQL_DEBUG |
Debug-trace options when debugging. |
MYSQL_HISTFILE |
The path to the mysql history file. |
MYSQL_HOST |
Default host name used by the mysql command-line prompt.
|
MYSQL_PWD |
The default password when connecting to mysqld. Note that
use of this is insecure! |
MYSQL_TCP_PORT |
The default TCP/IP port. |
MYSQL_UNIX_PORT |
The default socket; used for connections to localhost.
|
PATH |
Used by the shell to finds the MySQL programs. |
TMPDIR |
The directory where temporary tables/files are created. |
TZ |
This should be set to your local time zone. See section A.4.6 Time Zone Problems. |
UMASK_DIR |
The user-directory creation mask when creating directories. Note that
this is ANDed with UMASK! |
UMASK |
The user-file creation mask when creating files. |
USER |
The default user on Windows to use when connecting to
mysqld. |
A regular expression (regex) is a powerful way of specifying a complex search.
MySQL uses Henry Spencer's implementation of regular expressions, which is aimed at conformance with POSIX 1003.2. MySQL uses the extended version.
This is a simplistic reference that skips the details. To get more exact
information, see Henry Spencer's regex(7) manual page that is
included in the source distribution. See section C
Credits.
A regular expression describes a set of strings. The simplest regexp is one
that has no special characters in it. For example, the regexp hello
matches hello and nothing else.
Non-trivial regular expressions use certain special constructs so that they
can match more than one string. For example, the regexp hello|word
matches either the string hello or the string word.
As a more complex example, the regexp B[an]*s matches any of the
strings Bananas, Baaaaas, Bs, and any
other string starting with a B, ending with an s, and
containing any number of a or n characters in between.
A regular expression may use any of the following special characters/constructs:
^
mysql> select "fo\nfo" REGEXP "^fo$"; -> 0 mysql> select "fofo" REGEXP "^fo"; -> 1
$
mysql> select "fo\no" REGEXP "^fo\no$"; -> 1 mysql> select "fo\no" REGEXP "^fo$"; -> 0
.
mysql> select "fofo" REGEXP "^f.*"; -> 1 mysql> select "fo\nfo" REGEXP "^f.*"; -> 1
a*
a characters. mysql> select "Ban" REGEXP "^Ba*n"; -> 1 mysql> select "Baaan" REGEXP "^Ba*n"; -> 1 mysql> select "Bn" REGEXP "^Ba*n"; -> 1
a+
a characters. mysql> select "Ban" REGEXP "^Ba+n"; -> 1 mysql> select "Bn" REGEXP "^Ba+n"; -> 0
a?
a character. mysql> select "Bn" REGEXP "^Ba?n"; -> 1 mysql> select "Ban" REGEXP "^Ba?n"; -> 1 mysql> select "Baan" REGEXP "^Ba?n"; -> 0
de|abc
de or abc. mysql> select "pi" REGEXP "pi|apa"; -> 1 mysql> select "axe" REGEXP "pi|apa"; -> 0 mysql> select "apa" REGEXP "pi|apa"; -> 1 mysql> select "apa" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pi" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pix" REGEXP "^(pi|apa)$"; -> 0
(abc)*
abc. mysql> select "pi" REGEXP "^(pi)*$"; -> 1 mysql> select "pip" REGEXP "^(pi)*$"; -> 0 mysql> select "pipi" REGEXP "^(pi)*$"; -> 1
{1}
{2,3}
a*
a{0,}.
a+
a{1,}.
a?
a{0,1}. i and no comma
matches a sequence of exactly i matches of the atom. An atom
followed by a bound containing one integer i and a comma matches
a sequence of i or more matches of the atom. An atom followed by
a bound containing two integers i and j matches a
sequence of i through j (inclusive) matches of the
atom. Both arguments must be in the range from 0 to
RE_DUP_MAX (default 255), inclusive. If there are two arguments,
the second must be greater than or equal to the first.
[a-dX]
[^a-dX]
a, b, c, d or
X. To include a literal ] character, it must
immediately follow the opening bracket [. To include a literal
- character, it must be written first or last. So
[0-9] matches any decimal digit. Any character that does not have
a defined meaning inside a [] pair has no special meaning and
matches only itself. mysql> select "aXbc" REGEXP "[a-dXYZ]"; -> 1 mysql> select "aXbc" REGEXP "^[a-dXYZ]$"; -> 0 mysql> select "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1 mysql> select "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0 mysql> select "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1 mysql> select "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0
[[.characters.]]
ch
collating element, then the regular expression [[.ch.]]*c matches
the first five characters of chchcc.
[=character_class=]
o and (+) are the members of an equivalence class,
then [[=o=]], [[=(+)=]], and [o(+)] are
all synonymous. An equivalence class may not be an endpoint of a range.
[:character_class:]
[: and :] stands for the list of all characters
belonging to that class. Standard character class names are:
| Name | Name | Name |
| alnum | digit | punct |
| alpha | graph | space |
| blank | lower | upper |
| cntrl | xdigit |
ctype(3) manual page. A locale may provide others.
A character class may not be used as an endpoint of a range. mysql> select "justalnums" REGEXP "[[:alnum:]]+"; -> 1 mysql> select "!!" REGEXP "[[:alnum:]]+"; -> 0
[[:<:]]
[[:>:]]
ctype(3)) or an underscore
(_). mysql> select "a word a" REGEXP "[[:<:]]word[[:>:]]"; -> 1 mysql> select "a xword a" REGEXP "[[:<:]]word[[:>:]]"; -> 0
mysql> select "weeknights" REGEXP "^(wee|week)(knights|nights)$"; -> 1
Version 2, June 1991
Copyright © 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
9.4 NO WARRANTY
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does. Copyright (C) yyyy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
Version 2.1, February 1999
Copyright © 1991, 1999 Free Software Foundation, Inc. 59 Temple Place -- Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. [This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2, hence the version number 2.1.]
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public Licenses are intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users.
This license, the Lesser General Public License, applies to some specially designated software--typically libraries--of the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest you first think carefully about whether this license or the ordinary General Public License is the better strategy to use in any particular case, based on the explanations below.
When we speak of free software, we are referring to freedom of use, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish); that you receive source code or can get it if you want it; that you can change the software and use pieces of it in new free programs; and that you are informed that you can do these things.
To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to surrender these rights. These restrictions translate to certain responsibilities for you if you distribute copies of the library or if you modify it.
For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link other code with the library, you must provide complete object files to the recipients, so that they can relink them with the library after making changes to the library and recompiling it. And you must show them these terms so they know their rights.
We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which gives you legal permission to copy, distribute and/or modify the library.
To protect each distributor, we want to make it very clear that there is no warranty for the free library. Also, if the library is modified by someone else and passed on, the recipients should know that what they have is not the original version, so that the original author's reputation will not be affected by problems that might be introduced by others.
Finally, software patents pose a constant threat to the existence of any free program. We wish to make sure that a company cannot effectively restrict the users of a free program by obtaining a restrictive license from a patent holder. Therefore, we insist that any patent license obtained for a version of the library must be consistent with the full freedom of use specified in this license.
Most GNU software, including some libraries, is covered by the ordinary GNU General Public License. This license, the GNU Lesser General Public License, applies to certain designated libraries, and is quite different from the ordinary General Public License. We use this license for certain libraries in order to permit linking those libraries into non-free programs.
When a program is linked with a library, whether statically or using a shared library, the combination of the two is legally speaking a combined work, a derivative of the original library. The ordinary General Public License therefore permits such linking only if the entire combination fits its criteria of freedom. The Lesser General Public License permits more lax criteria for linking other code with the library.
We call this license the Lesser General Public License because it does Less to protect the user's freedom than the ordinary General Public License. It also provides other free software developers Less of an advantage over competing non-free programs. These disadvantages are the reason we use the ordinary General Public License for many libraries. However, the Lesser license provides advantages in certain special circumstances.
For example, on rare occasions, there may be a special need to encourage the widest possible use of a certain library, so that it becomes a de-facto standard. To achieve this, non-free programs must be allowed to use the library. A more frequent case is that a free library does the same job as widely used non-free libraries. In this case, there is little to gain by limiting the free library to free software only, so we use the Lesser General Public License.
In other cases, permission to use a particular library in non-free programs enables a greater number of people to use a large body of free software. For example, permission to use the GNU C Library in non-free programs enables many more people to use the whole GNU operating system, as well as its variant, the GNU/Linux operating system.
Although the Lesser General Public License is Less protective of the users' freedom, it does ensure that the user of a program that is linked with the Library has the freedom and the wherewithal to run that program using a modified version of the Library.
The precise terms and conditions for copying, distribution and modification follow. Pay close attention to the difference between a ``work based on the library'' and a ``work that uses the library''. The former contains code derived from the library, whereas the latter must be combined with the library in order to run.
9.6 NO WARRANTY
If you develop a new library, and you want it to be of the greatest possible use to the public, we recommend making it free software that everyone can redistribute and change. You can do so by permitting redistribution under these terms (or, alternatively, under the terms of the ordinary General Public License).
To apply these terms, attach the following notices to the library. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found.
one line to give the library's name and an idea of what it does. Copyright (C) year name of author This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
Also add information on how to contact you by electronic and paper mail.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the library, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker. signature of Ty Coon, 1 April 1990 Ty Coon, President of Vice
That's all there is to it!
CC
environment variable
CXX
environment variable
DBI_TRACE
environment variable
CC
CXX
DBI_TRACE
HOME, environment
variable, HOME
MYSQL_DEBUG, environment
variable, MYSQL_DEBUG
MYSQL_HISTFILE, environment
variable, MYSQL_HISTFILE
MYSQL_HOST
MYSQL_PWD, environment
variable, MYSQL_PWD, environment
variable, MYSQL_PWD
MYSQL_TCP_PORT, environment
variable, MYSQL_TCP_PORT, environment
variable, MYSQL_TCP_PORT
MYSQL_UNIX_PORT, environment
variable, MYSQL_UNIX_PORT, environment
variable, MYSQL_UNIX_PORT
USER
HOME
environment variable, HOME
environment variable
my_init()
mysql_affected_rows()
mysql_change_user()
mysql_character_set_name()
mysql_close()
mysql_connect()
mysql_create_db()
mysql_data_seek()
MYSQL_DEBUG
environment variable, MYSQL_DEBUG
environment variable
mysql_debug()
mysql_drop_db()
mysql_dump_debug_info()
mysql_eof()
mysql_errno()
mysql_error()
mysql_escape_string()
mysql_fetch_field()
mysql_fetch_field_direct()
mysql_fetch_fields()
mysql_fetch_lengths()
mysql_fetch_row()
mysql_field_count(),
mysql_field_count()
mysql_field_seek()
mysql_field_tell()
mysql_free_result()
mysql_get_client_info()
mysql_get_host_info()
mysql_get_proto_info()
mysql_get_server_info()
MYSQL_HISTFILE
environment variable, MYSQL_HISTFILE
environment variable
MYSQL_HOST
environment variable
mysql_info()
mysql_init()
mysql_insert_id()
mysql_kill()
mysql_list_dbs()
mysql_list_fields()
mysql_list_processes()
mysql_list_tables()
mysql_num_fields()
mysql_num_rows()
mysql_options()
mysql_ping()
MYSQL_PWD
environment variable, MYSQL_PWD
environment variable, MYSQL_PWD
environment variable
mysql_query(),
mysql_query()
mysql_real_connect()
mysql_real_escape_string()
mysql_real_query()
mysql_reload()
mysql_row_seek()
mysql_row_tell()
mysql_select_db()
mysql_server_end()
mysql_server_init()
mysql_shutdown()
mysql_stat()
mysql_store_result(),
mysql_store_result()
MYSQL_TCP_PORT
environment variable, MYSQL_TCP_PORT
environment variable, MYSQL_TCP_PORT
environment variable
mysql_thread_end()
mysql_thread_id()
mysql_thread_init()
MYSQL_UNIX_PORT
environment variable, MYSQL_UNIX_PORT
environment variable, MYSQL_UNIX_PORT
environment variable
mysql_use_result()
USER
environment variable
ACID
GROUP BY clauses
ORDER BY clauses
AUTO_INCREMENT,
and NULL values batch,
mysql option
BDB
table type
BDB
tables
Berkeley_db
table type
Binlog_Dump
BLOB
columns, default values
BLOB
columns, indexing
BLOB,
inserting binary data
BLOB,
size
mysqld server
gcc
cc1plus
problems
character-sets-dir,
mysql option
mysql
gcc
compress,
mysql option
config.cache
file
configure
script
configure,
running after prior invocation
connect_timeout
variable
Contrib
directory
database,
mysql option
db
table, sorting
DBI
interface
DBI
Perl module
DBI/DBD
debug-info,
mysql option
debug,
mysql option
BLOB and TEXT columns
default-character-set,
mysql option
mysql.sock
SHOW
enable-named-commands,
mysql option
myisamchk output
execute,
mysql option
fatal
signal 11
config.cache
tmp
my.cnf
force,
mysql option
SELECT and WHERE clauses
gcc
GROUP
BY, aliases in
GROUP
BY, extensions to ANSI SQL, GROUP
BY, extensions to ANSI SQL
HEAP
table type
help,
mysql option
host
table
host
table, sorting
host,
mysql option
html,
mysql option ignore-space,
mysql option
BLOB columns
IS NULL
LIKE
NULL values
TEXT columns
InnoDB
table type
InnoDB
tables
ISAM
table type
mysqlclient
make_binary_distribution,
make_binary_distribution
max_allowed_packet
max_join_size
MERGE
table type
msql2mysql,
msql2mysql
my.cnf
file
MyISAM
table type
myisamchk,
myisamchk,
myisamchk
myisamchk,
example output
myisamchk,
options
myisampack,
myisampack
mysladmn
mysql
mysql
command line options
mysql.sock,
protection
mysql_fix_privilege_tables
mysql_install_db,
mysql_install_db
mysql_install_db
script
mysqlaccess,
mysqlaccess
mysqladmin,
mysqladmin,
mysqladmin,
mysqladmin,
mysqladmin,
mysqladmin,
mysqladmin
mysqlbug,
mysqlbug
mysqlbug
script
mysqlbug
script, location
mysqlclient
library
mysqld,
mysqld
mysqld
options
mysqld
server, buffer sizes
mysqld,
starting
mysqld-max
mysqld_multi
mysqldump,
mysqldump,
mysqldump,
mysqldump
mysqlimport,
mysqlimport,
mysqlimport,
mysqlimport,
mysqlimport
mysqlshow,
mysqlshow
net_buffer_length
mysql.user table
no-auto-rehash,
mysql option
no-named-commands,
mysql option
no-pager,
mysql option
no-tee,
mysql option
NULL
values, and indexes
NULL
values, vs. empty values
NULL,
testing for null, NULL,
testing for null, NULL,
testing for null, NULL,
testing for null
NULL
values, and AUTO_INCREMENT columns
NULL
values, and TIMESTAMP columns
one-database,
mysql option
mysql
myisamchk
ORDER
BY, aliases in
pack_isam
pager,
mysql option
password,
mysql option
port,
mysql option
DATE columns
quick,
mysql option
raw,
mysql option
replace,
replace
configure after prior invocation
safe-mode
command
safe-updates,
mysql option
safe_mysqld
mysql_install_db
mysqlbug
SELECT,
Query Cache
select_limit
set-variable,
mysql option
silent,
mysql option
skip-column-names,
mysql option
skip-line-numbers,
mysql option
socket,
mysql option
sql_yacc.cc
problems
mysqld
mysql
table,
mysql option
BDB
Berkeley DB
HEAP
host
tee,
mysql option
TEXT
columns, default values
TEXT
columns, indexing
TEXT,
size
connect_timeout variable
TIMESTAMP,
and NULL values
unbuffered,
mysql option
user
table, sorting
user,
mysql option
VARCHAR,
size
mysqld
verbose,
mysql option
version,
mysql option
vertical,
mysql option
wait,
mysql option
mysql.columns_priv table
mysql.db table
mysql.host table
mysql.tables_priv table
LIKE
mysql.user table
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