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1 General Information

The MySQL (R) software delivers a very fast, multi-threaded, multi-user, and robust SQL (Structured Query Language) database server. MySQL Server 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.

The MySQL software is Dual Licensed. Users can choose to use the MySQL software as an Open Source/Free Software product under the terms of the GNU General Public License (http://www.fsf.org/licenses/) or can purchase a standard commercial license from MySQL AB. See section 1.4 MySQL Support and Licensing.

The MySQL web site (http://www.mysql.com/) provides the latest information about the MySQL software.

The following list describes some sections of particular interest in this manual:


Reports of errors (often called bugs), as well as questions and comments, should be sent to the general MySQL mailing list. See section The MySQL Mailing Lists. See section How to Report Bugs or Problems.

The mysqlbug script should be used to generate bug reports on Unix. (Windows distributions contain a file `mysqlbug.txt' in the base directory that can be used as a template for a bug report.)

For source distributions, the mysqlbug script can be found in the `scripts' directory. For binary distributions, mysqlbug can be found in the `bin' directory (`/usr/bin' for the MySQL-server RPM package).

If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending an email message to security@mysql.com.

1.1 About This Manual

This is the MySQL reference manual; it documents MySQL up to Version 5.0.0-alpha. Functional changes are always indicated with reference to the version, so this manual is also suitable if you are using an older version of the MySQL software (such as 3.23 or 4.0-production). There are also references for version 5.0 (development).

Being a reference manual, it does not provide general instruction on SQL or relational database concepts. It also will not teach you how to use your operating system or command line interpreter.

As the MySQL Database Software is under constant development, the manual is also updated frequently. The most recent version of this manual is available at http://www.mysql.com/documentation/ in many different formats, including HTML, PDF, and Windows HLP 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.

The index can assist you in finding information in the manual. For online use, you can try the searchable version of the manual available at http://www.mysql.com/doc/.

If you have any suggestions concerning additions or corrections to this manual, please send them to the documentation team at docs@mysql.com.

This manual was initially written by David Axmark and Michael (Monty) Widenius. It is now maintained by the MySQL Documentation Team, consisting of Arjen Lentz, Paul DuBois and Stefan Hinz. For the many other contributors, see section B Credits.

The copyright (2004) to this manual is owned by the Swedish company MySQL AB. See section 1.4.2 Copyrights and Licenses Used by MySQL.

1.1.1 Conventions Used in This Manual

This manual uses certain typographical conventions:

Constant-width font is used for command names and options; SQL statements; database, table, and column names; C and Perl code; and environment variables. Example: ``To see how mysqladmin works, invoke it with the --help option.''
Constant-width font with surrounding quotes is used for filenames and pathnames. Example: ``The distribution is installed under the `/usr/local/' directory.''
Constant-width font with surrounding quotes is also used to indicate character sequences. Example: ``To specify a wildcard, use the `%' character.''
Italic font is used for emphasis, like this.
Boldface font is used in table headings and to convey especially strong emphasis.

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 statement that you execute from the mysql client program:

shell> type a shell command here
mysql> type a mysql statement here

The ``shell'' is your command interpreter. On Unix, this is typically a program such as sh or csh. On Windows, the equivalent is command.com or cmd.exe, typically run in a Windows console.

Note that to enter a command or statement from an example, you do not type the prompt shown in the example.

Commands to set shell variables are shown using Bourne shell syntax. If you are using csh or tcsh, you will need to issue commands somewhat 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 or tcsh, you would execute the sequence like this:

shell> setenv VARNAME value
shell> some_command

Database, table, and column names must often 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 keywords are not case sensitive and may be written in uppercase or lowercase. This manual uses uppercase.

In syntax descriptions, square brackets (`[' and `]') are used to indicate optional words or clauses. For example, in the following statement, IF EXISTS is optional:


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 `]'):


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}

An ellipsis (...) indicates the omission of a section of a statement, typically to provide a shorter version of more complex syntax. For example, INSERT ... SELECT is shorthand for the form of INSERT statement that is followed by a SELECT statement.

An ellipsis can also indicate that the preceding syntax element of a statement may be repeated. In the following example, multiple reset_option values may be given, with each of those after the first preceded by commas:

RESET reset_option [,reset_option] ...

1.2 Overview of the MySQL Database Management System

MySQL, the most popular Open Source SQL database management system, is developed, distributed, and supported by MySQL AB. MySQL AB is a commercial company, founded by the MySQL developers, that builds its business by providing services around the MySQL database management system. See section 1.3 Overview of MySQL AB.

The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL software and MySQL AB.

MySQL is a database management system.
A database is a structured collection of data. It may be anything from a simple shopping list to a picture gallery or the vast amounts of information in a corporate network. To add, access, and process data stored in a computer database, you need a database management system such as MySQL Server. Since computers are very good at handling large amounts of data, database management systems play a central role in computing, as stand-alone utilities or as parts of other applications.
MySQL is a relational database management system.
A relational database stores data in separate tables rather than putting all the data in one big storeroom. This adds speed and flexibility. The SQL part of ``MySQL'' stands for ``Structured Query Language''. SQL is the most common standardized language used to access databases and is defined by the ANSI/ISO SQL Standard.(The SQL standard has been evolving since 1986 and several versions exist. In this manual, ``SQL-92'' refers to the standard released in 1992, ``SQL-99'' refers to the standard released in 1999, and ``SQL:2003'' refers to the next version of the standard. We use the term ``the SQL standard'' to mean the current version of the SQL Standard at any time.)
MySQL software is Open Source.
Open Source means that it is possible for anyone to use and modify the software. Anybody can download the MySQL software from the Internet and use it without paying anything. If you wish, you may study the source code and change it to suit your needs. The MySQL software uses the GPL (GNU General Public License), http://www.fsf.org/licenses/, to define what you may and may not do with the software in different situations. If you feel uncomfortable with the GPL or need to embed MySQL code into a commercial application, you can buy a commercially licensed version from us. See section 1.4.3 MySQL Licenses.
Why use the MySQL Database Server?
The MySQL Database Server is very fast, reliable, and easy to use. If that is what you are looking for, you should give it a try. MySQL Server also has a practical set of features developed in close cooperation with our users. You can find a performance comparison of MySQL Server with other database managers on our benchmark page. See section 7.1.4 The MySQL Benchmark Suite. MySQL Server was originally developed to handle large databases much faster than existing solutions and has been successfully used in highly demanding production environments for several years. Though under constant development, MySQL Server today offers a rich and useful set of functions. Its connectivity, speed, and security make MySQL Server highly suited for accessing databases on the Internet.
The technical features of MySQL Server
The MySQL Database Software is a client/server system that consists of a multi-threaded SQL server that supports different backends, several different client programs and libraries, administrative tools, and a wide range of application programming interfaces (APIs). We also provide MySQL Server as a multi-threaded library which you can link into your application to get a smaller, faster, easier-to-manage product.
There is a large amount of contributed MySQL software available.
It is very likely that you will find that your favorite application or language already supports the MySQL Database Server.

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 localized way.

1.2.1 History of MySQL

We 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 or 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 designed to allow third-party code that was written for use with mSQL to be ported easily for use with MySQL.

The derivation of the name MySQL is not clear. Our base directory and a large number of our libraries and tools have had the prefix ``my'' for well over 10 years. However, co-founder Monty Widenius's daughter is also named My. Which of the two gave its name to MySQL is still a mystery, even for us.

The name of the MySQL Dolphin (our logo) is Sakila. Sakila was chosen by the founders of MySQL AB from a huge list of names suggested by users in our ``Name the Dolphin'' contest. The winning name was submitted by Ambrose Twebaze, an open source software developer from Swaziland, Africa. According to Ambrose, the name Sakila has its roots in SiSwati, the local language of Swaziland. Sakila is also the name of a town in Arusha, Tanzania, near Ambrose's country of origin, Uganda.

1.2.2 The Main Features of MySQL

The following list describes some of the important characteristics of the MySQL Database Software. See section 1.5.1 MySQL 4.0 in a Nutshell.

Internals and Portability
Column Types
Commands and Functions
Scalability and Limits
Clients and Tools

1.2.3 MySQL Stability

This section addresses the questions ``How stable is MySQL Server?'' and ``Can I depend on MySQL Server 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.

The original code stems back to the early 1980s. It provides a stable code base, and the ISAM table format used by the original storage engine remains backward-compatible. At TcX, the predecessor of MySQL AB, MySQL code has worked in projects since mid-1996, without any problems. When the MySQL Database Software initially was released to a wider public, our new users quickly found some pieces of ``untested code''. Each new release since then has had fewer portability problems (even though each new release has also had many new features).

Each release of the MySQL Server has been usable. Problems have occurred only when users try code from the ``gray zones.'' Naturally, new users don't know what the gray zones are; this section therefore attempts to document those areas that are currently known. The descriptions mostly deal with Version 3.23 and 4.0 of MySQL Server. All known and reported bugs are fixed in the latest version, with the exception of those listed in the bugs section, which are design-related. See section 1.8.7 Known Errors and Design Deficiencies in MySQL.

The MySQL Server design is multi-layered with independent modules. Some of the newer modules are listed here with an indication of how well-tested each of them is:

Replication -- Gamma
Large groups of servers using replication are in production use, with good results. Work on enhanced replication features is continuing in MySQL 5.x.
InnoDB tables -- Stable (in 3.23 from 3.23.49)
The InnoDB transactional storage engine has been declared stable in the MySQL 3.23 tree, starting from version 3.23.49. InnoDB is being used in large, heavy-load production systems.
BDB tables -- Gamma
The Berkeley DB code is very stable, but we are still improving the BDB transactional storage engine interface in MySQL Server, so it will take some time before this is as well tested as the other table types.
Full-text searches -- Beta
Full-text searching works but is not yet widely used. Important enhancements have been implemented in MySQL 4.0.
Connector/ODBC 3.51 (uses ODBC SDK 3.51) -- Stable
In wide production use. Some issues brought up appear to be application-related and independent of the ODBC driver or underlying database server.
Automatic recovery of MyISAM tables -- Gamma
This status applies only to the new code in the MyISAM storage engine that checks if the table was closed properly on open and executes an automatic check/repair of the table if it wasn't.
Bulk-insert -- Alpha
New feature in MyISAM tables in MySQL 4.0 for faster insert of many rows.
Locking -- Gamma
This is very system-dependent. On some systems there are big problems using standard operating system locking (fcntl()). In these cases, you should run mysqld with the --skip-external-locking flag. Problems are known to occur on some Linux systems, and on SunOS when using NFS-mounted filesystems.

Paying customers receive high-quality support directly from MySQL AB. MySQL AB also provides the MySQL mailing list as a community resource where anyone may ask questions.

Bugs are usually fixed right away with a patch. For serious bugs, there is almost always a new release.

1.2.4 How Big MySQL Tables Can Be

MySQL Version 3.22 had a 4 GB (4 gigabyte) limit on table size. With the MyISAM storage engine in MySQL Version 3.23, the maximum table size was increased to 8 million terabytes (2 ^ 63 bytes). With this larger allowed table size, the maximum effective table size for MySQL databases now normally is determined by operating system constraints on file sizes, not by MySQL internal limits.

The InnoDB storage engine maintains InnoDB tables within a tablespace that can be created from several files. This allows a table to exceed the maximum individual file size. The tablespace can include raw disk partitions, which allows extremely large tables. The maximum tablespace size is 64 TB.

The following table lists some examples of operating system file-size limits:

Operating System File-Size Limit
Linux-Intel 32-bit 2 GB, much more when using LFS
Linux-Alpha 8 TB (?)
Solaris 2.5.1 2 GB (4GB possible with patch)
Solaris 2.6 4 GB (can be changed with flag)
Solaris 2.7 Intel 4 GB
Solaris 2.7 UltraSPARC 512 GB

On Linux 2.2, you can get MyISAM tables larger than 2 GB in size by using the LFS patch for the ext2 filesystem. On Linux 2.4, patches also exist for ReiserFS to get support for big files. Most current Linux distributions are based on kernel 2.4 and already include all the required Large File Support (LFS) patches. However, the maximum available file size still depends on several factors, one of them being the file system used to store MySQL tables.

For a very detailed overview about LFS in Linux, have a look at Andreas Jaeger's ``Large File Support in Linux'' page at http://www.suse.de/~aj/linux_lfs.html.

By default, MySQL creates MyISAM tables with an internal structure that allows a maximum size of about 4 GB. 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 13.5.3 SHOW Syntax.

If you need a MyISQM table that will be larger than 4 GB in size (and your operating system supports large files), the CREATE TABLE statement allows AVG_ROW_LENGTH and MAX_ROWS options. See section 13.2.5 CREATE TABLE Syntax. You can also change these options with ALTER TABLE after the table has been created, to increase the table's maximum allowable size. See section 13.2.2 ALTER TABLE Syntax.

Other ways to work around file-size limits for MyISAM tables are as follows:

1.2.5 Year 2000 Compliance

The MySQL Server itself has no problems with Year 2000 (Y2K) compliance:

The following simple demonstration illustrates that MySQL Server doesn't have any problems with dates until after the year 2030:

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)

    -> ('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)

The final TIMESTAMP column value is zero because the final year (2050) exceeds the TIMESTAMP maximum. The TIMESTAMP datatype, which is used to store the current time, supports values that range from 19700101000000 to 20300101000000 on 32-bit machines (signed value). On 64-bit machines, TIMESTAMP handles values up to 2106 (unsigned value).

The example also shows that the DATE and DATETIME datatypes have no problems with the dates used. They handle dates through the year 9999.

Although MySQL Server itself is Y2K-safe, you may run into problems if you use it with applications that are 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.

Thus, even though MySQL Server has no Y2K problems, it is the application's responsibility to provide unambiguous input. See section 11.2.1 Y2K Issues and Date Types for MySQL Server's rules for dealing with ambiguous date input data that contains 2-digit year values.

1.3 Overview of MySQL AB

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.

The developers of the MySQL server are all employed by the company. We are a virtual organization with people in a dozen countries around the world. We communicate extensively over the Internet every day with one another and with our users, supporters, and partners.

We are dedicated to developing the MySQL database software and promoting it 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 Overview of the MySQL Database Management System.

The MySQL core values show our dedication to MySQL and Open Source.

We want the MySQL Database Software to be:

MySQL AB and the people at MySQL AB:

The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.

By the way, the ``AB'' part of the company name is the acronym for the Swedish ``aktiebolag'', or ``stock company.'' It translates to ``MySQL, Inc.'' In fact, MySQL Inc. and MySQL GmbH are examples of MySQL AB subsidiaries. They are located in the US and Germany, respectively.

1.3.1 The Business Model and Services of 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:

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. Support

MySQL AB is run and owned by the founders and main developers of the MySQL database. The developers are committed to providing support to customers and other users in order to stay in touch with their needs and problems. All our support is provided 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.

For more information and ordering support at various levels, see http://www.mysql.com/support/ or contact our sales staff at sales@mysql.com. Training and Certification

MySQL AB delivers MySQL and related training worldwide. We offer both open courses and in-house courses tailored to the specific needs of your company. MySQL Training is also available through our partners, the Authorized MySQL Training Centers.

Our training material uses the same example databases used in our documentation and our sample applications, and 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 MySQL application goals. You will also:

If you are interested in our training as a potential participant or as a training partner, please visit the training section at http://www.mysql.com/training/ or contact us at: training@mysql.com.

For details about the MySQL Certification Program, please see http://www.mysql.com/certification/. Consulting

MySQL AB and its Authorized Partners offer consulting services to users of MySQL Server and to those who embed MySQL Server 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 Server 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 not only covers MySQL Server---it also 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://www.mysql.com/consulting/ or contact our consulting staff at consulting@mysql.com. Commercial Licenses

The MySQL database is released under the GNU General Public License (GPL). This means that the MySQL software can be used free of charge under the GPL. If you do not want to be bound by the GPL terms (such as the requirement that your application must also be GPL), you may purchase a commercial license for the same product from MySQL AB; see http://www.mysql.com/products/pricing.html. Since MySQL AB owns the copyright to the MySQL source code, we are able to employ Dual Licensing, which means that the same product is available 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 Licenses.

We also sell commercial licenses of third-party Open Source GPL software that adds value to MySQL Server. A good example is the InnoDB transactional storage engine that offers ACID support, row-level locking, crash recovery, multi-versioning, foreign key support, and more. See section 14.4 InnoDB Tables. Partnering

MySQL AB has a worldwide partner program that covers training courses, consulting and support, publications, plus reselling and distributing MySQL and related products. MySQL AB Partners get visibility on the http://www.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 email 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://www.mysql.com/) is popular among developers and users. In December 2003, we served 16 million page views. Our visitors represent a group that makes purchase decisions and recommendations for both software and hardware. Twelve percent of our visitors authorize purchase decisions, and only nine percent are not involved in purchase decisions at all. More than 65% have made one or more online business purchases within the last half-year, and 70% plan to make one in the next few months.

1.3.2 Contact Information

The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.

For press services and inquiries not covered in our News releases (http://www.mysql.com/news/), please send email 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 the MySQL software. For more information, see section 1.4.1 Support Offered by MySQL AB. On our web site, see http://www.mysql.com/support/, or send an email message to sales@mysql.com.

For information about MySQL training, please visit the training section at http://www.mysql.com/training/. If you have restricted access to the Internet, please contact the MySQL AB training staff via email at training@mysql.com. See section Training and Certification.

For information on the MySQL Certification Program, please see http://www.mysql.com/certification/. See section Training and Certification.

If you're interested in consulting, please visit the consulting section of our web site at http://www.mysql.com/consulting/. If you have restricted access to the Internet, please contact the MySQL AB consulting staff via email at consulting@mysql.com. See section 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. More information about licensing can be found at http://www.mysql.com/products/pricing.html. 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://www.mysql.com/) or send email to licensing@mysql.com (for licensing questions) or to sales@mysql.com (for sales inquiries). See section 1.4.3 MySQL Licenses.

If you represent a business that is interested in partnering with MySQL AB, please send email to partner@mysql.com. See section Partnering.

For more information on the MySQL trademark policy, refer to http://www.mysql.com/company/trademark.html or send email to 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://www.mysql.com/company/jobs/), please send email to jobs@mysql.com. Please do not send your CV as an attachment, but rather as plain text at the end of your email message.

For general discussion among our many users, please direct your attention to the appropriate mailing list. See section 1.7.1 MySQL Mailing Lists.

Reports of errors (often called bugs), as well as questions and comments, should be sent to the general MySQL mailing list. See section The MySQL Mailing Lists. If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending an email message to security@mysql.com. See section How to Report Bugs or Problems.

If you have benchmark results that we can publish, please contact us via email at benchmarks@mysql.com.

If you have suggestions concerning additions or corrections to this manual, please send them to the manual team via email at docs@mysql.com.

For questions or comments about the workings or content of the MySQL web site (http://www.mysql.com/), please send email to webmaster@mysql.com.

MySQL AB has a privacy policy, which can be read at http://www.mysql.com/company/privacy.html. For any queries regarding this policy, please send email to privacy@mysql.com.

For all other inquires, please send an email to info@mysql.com.

1.4 MySQL Support and Licensing

This section describes MySQL support and licensing arrangements.

1.4.1 Support Offered by MySQL AB

Technical support from MySQL AB means individualized 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 software 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 the impact of operating system or networking issues on MySQL, set up best practices for backup and recovery, utilize APIs, and so on. Our support covers only the MySQL server and our own utilities, not third-party products that access the MySQL server, though we try to help with these where we can.

Detailed information about our various support options is given at http://www.mysql.com/support/, where support contracts can also be ordered online. If you have restricted access to the Internet, please contact our sales staff via email at sales@mysql.com.

Technical support is like life insurance. You can live happily without it for years. However, when your hour arrives, it becomes critically important, but it's too late to buy it. If you use MySQL Server for important applications and encounter sudden difficulties, it may be too time consuming to figure out all the answers yourself. You may need immediate access to the most experienced MySQL troubleshooters available, those employed by MySQL AB.

1.4.2 Copyrights and Licenses Used by MySQL

MySQL AB owns the copyright to the MySQL source code, the MySQL logos and trademarks and this manual. See section 1.3 Overview of MySQL AB. Several different licenses are relevant to the MySQL distribution:

  1. All the MySQL-specific source in the server, the mysqlclient library and the client, as well as the GNU readline library is covered by the GNU General Public License. See section G GNU General Public License. The text of this license can be found as the file `COPYING' in the distribution.
  2. The GNU getopt library is covered by the GNU Lesser General Public License. See http://www.fsf.org/licenses/.
  3. Some parts of the source (the regexp library) are covered by a Berkeley-style copyright.
  4. Older versions of MySQL (3.22 and earlier) are subject to a stricter license (http://www.mysql.com/products/mypl.html). See the documentation of the specific version for information.
  5. The MySQL reference manual is currently not distributed under a GPL-style license. Use of the manual is subject to the following terms: Please send an email message to docs@mysql.com for more information or if you are interested in doing a translation.

For information about how the MySQL licenses work in practice, please refer to section 1.4.3 MySQL Licenses. Also see section 1.4.4 MySQL AB Logos and Trademarks.

1.4.3 MySQL Licenses

The MySQL software is released under the GNU General Public License (GPL), which is probably the best known Open Source license. The formal terms of the GPL license can be found at http://www.fsf.org/licenses/. See also http://www.fsf.org/licenses/gpl-faq.html and http://www.gnu.org/philosophy/enforcing-gpl.html.

Since the MySQL software 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/. See http://www.mysql.com/products/licensing.html for more information.

Older versions of MySQL (3.22 and earlier) are subject to a stricter license (http://www.mysql.com/products/mypl.html). See the documentation of the specific version for information.

Please note that the use of the MySQL software 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. Using the MySQL Software Under a Commercial License

The GPL license is contagious in the sense that when a program is linked to a GPL program all the source code for all the parts of the resulting product must also be released under the GPL. If you do not follow this GPL requirement, you break the license terms and forfeit your right to use the GPL program altogether. You also risk damages.

You need a commercial license:

If you require a license, you will need one for each installation of the MySQL software. 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.

For commercial licenses, please visit our website at http://www.mysql.com/products/licensing.html. For support contracts, see http://www.mysql.com/support/. If you have special needs or you have restricted access to the Internet, please contact our sales staff via email at sales@mysql.com. Using the MySQL Software for Free Under GPL

You can use the MySQL software for free under the GPL if you adhere to the conditions of the GPL. For additional details, including answers to common questions about the GPL, see the generic FAQ from the Free Software Foundation at http://www.fsf.org/licenses/gpl-faq.html. Common uses of the GPL include:

If your use of MySQL database software does not require a commercial license, we encourage you to purchase support from MySQL AB anyway. This way you contribute toward MySQL development and also gain immediate advantages for yourself. See section 1.4.1 Support Offered by MySQL AB.

If you use the MySQL database software in a commercial context such that you profit by its use, we ask that you further the development of the MySQL software by purchasing some level of support. We feel that if the MySQL database helps your business, it is reasonable to ask that you help MySQL AB. (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.)

1.4.4 MySQL AB Logos and Trademarks

Many users of the MySQL database want to display the MySQL AB dolphin logo on their web sites, 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://www.mysql.com/company/trademark.html. The Original MySQL Logo

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 management system, which is like 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. MySQL Logos that may be Used Without Written Permission

We have designed a set of special Conditional Use logos that may be downloaded from our web site at http://www.mysql.com/press/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 as follows:

Contact us via email at trademark@mysql.com to inquire about special arrangements to fit your needs. When You Need Written Permission to Use MySQL Logos

You need written permission from MySQL AB before using MySQL logos in the following cases:

Due to legal and commercial reasons we monitor the use of MySQL trademarks on products, books, and other items. We 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 AB Partnership Logos

MySQL partnership logos may be used only by companies and persons having a written partnership agreement with MySQL AB. Partnerships include certification as a MySQL trainer or consultant. For more information, please see section Partnering. Using the Word MySQL in Printed Text or Presentations

MySQL AB welcomes references to the MySQL database, but it should be noted that the word MySQL is a trademark of MySQL AB. Because of this, you must append the trademark symbol (TM) to the first or most prominent use of the word MySQL in a text and, where appropriate, state that MySQL is a trademark of MySQL AB. For more information, please refer to our trademark policy at http://www.mysql.com/company/trademark.html. Using the Word MySQL in Company and Product Names

Use of the word MySQL in product or company names or in Internet domain names is not allowed without written permission from MySQL AB.

1.5 MySQL Development Roadmap

This section provides a snapshot of the MySQL development roadmap, including major features implemented or planned for MySQL 4.0, 4.1, 5.0, and 5.1. The following sections provide information for each release series.

The production release series is MySQL 4.0, which was declared stable for production use as of Version 4.0.12, released in March 2003. This means that future 4.0 development will be limited only to making bug fixes. For the older MySQL 3.23 series, only critical bug fixes will be made.

Active MySQL development currently is taking place in the MySQL 4.1 and 5.0 release series. This means that new features are being added to MySQL 4.1 and MySQL 5.0. Both 4.1 and 5.0 are available now in alpha status.

Before upgrading from one release series to the next, please see the notes at section 2.5 Upgrading/Downgrading MySQL.

Plans for some of the most requested features are summarized in the following table.

Feature MySQL version
Unions 4.0
Subqueries 4.1
R-trees 4.1 (for MyISAM tables)
Stored procedures 5.0
Views 5.0 or 5.1
Cursors 5.0
Foreign keys 5.1 (already implemented in 3.23 for InnoDB)
Triggers 5.1
Full outer join 5.1
Constraints 5.1

1.5.1 MySQL 4.0 in a Nutshell

Long awaited by our users, MySQL Server 4.0 is now available in production status.

MySQL 4.0 is available for download from http://www.mysql.com/ and from our mirrors. MySQL 4.0 has been tested by a large number of users and is in production use at many large sites.

The major new features of MySQL Server 4.0 are geared toward our existing business and community users, enhancing the MySQL database software as the solution for mission-critical, heavy-load database systems. Other new features target the users of embedded databases. Features Available in MySQL 4.0

Speed enhancements
Embedded MySQL Server introduced
InnoDB storage engine as standard
New functionality
Standards compliance, portability, and migration
Usability enhancements
In the process of implementing features for new users, we have not forgotten requests from our loyal community of existing users.

The news section of this manual includes a more in-depth list of features. See section C.3 Changes in release 4.0.x (Production). The Embedded MySQL Server

The libmysqld embedded server library makes MySQL Server suitable for a vastly expanded realm of applications. By using this library, developers can embed MySQL Server into various applications and electronics devices, where the end user has no knowledge of there actually being an underlying database. Embedded MySQL Server is ideal for use behind the scenes in Internet appliances, public kiosks, turnkey hardware/software combination units, high performance Internet servers, self-contained databases distributed on CD-ROM, and so on.

Many users of libmysqld will benefit from the MySQL Dual Licensing. For those not wishing to be bound by the GPL, the software is also made available under a commercial license. The embedded MySQL library uses the same interface as the normal client library, so it is convenient and easy to use. See section 19.1.15 libmysqld, the Embedded MySQL Server Library.

1.5.2 MySQL 4.1 in a Nutshell

MySQL Server 4.0 laid the foundation for new features implemented in MySQL 4.1, such as subqueries and Unicode support, and for the work on stored procedures being done in version 5.0. These features come at the top of the wish list of many of our customers.

With these additions, critics of the MySQL Database Server have to be more imaginative than ever in pointing out deficiencies in the MySQL database management system. Already well-known for its stability, speed, and ease of use, MySQL Server will be able to fulfill the requirement checklists of very demanding buyers. Features Available in MySQL 4.1

The features listed in this section are implemented in MySQL 4.1. A few other features are still planned for MySQL 4.1. See section 1.6.1 New Features Planned for 4.1.

Most new features being coded are or will be available in MySQL 5.0. See section 1.6.2 New Features Planned for 5.0.

Support for subqueries and derived tables
Speed enhancements
New functionality
Standards compliance, portability, and migration
Usability enhancements

The news section of this manual includes a more in-depth list of features. See section C.2 Changes in release 4.1.x (Alpha). Stepwise Rollout

New features are being added to MySQL 4.1. The alpha version is already available for download. See section Ready for Immediate Development Use.

The set of features that are being added to version 4.1 is mostly fixed. Additional development is already ongoing for version 5.0. MySQL 4.1 will go through the steps of Alpha (during which time new features might still be added/changed), Beta (when we have feature freeze and only bug corrections will be done), and Gamma (indicating that a production release is just weeks ahead). At the end of this process, MySQL 4.1 will become the new production release. Ready for Immediate Development Use

MySQL 4.1 is currently in the alpha stage, and binaries are available for download at http://www.mysql.com/downloads/mysql-4.1.html. All binary releases pass our extensive test suite without any errors on the platforms on which we test. See section C.2 Changes in release 4.1.x (Alpha).

For those wishing to use the most recent development source for MySQL 4.1, we make our 4.1 BitKeeper repository publicly available. See section 2.3.3 Installing from the Development Source Tree.

1.5.3 MySQL 5.0, The Next Development Release

New development for MySQL is focused on the 5.0 release, featuring Stored Procedures and other new features. See section 1.6.2 New Features Planned for 5.0.

For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See section 2.3.3 Installing from the Development Source Tree. As of December 2003, binary builds of version 5.0 are also available.

1.6 MySQL and the Future (The TODO)

This section summarizes the features that we plan to implement in MySQL Server. The items are ordered by release series. Within a list, items are shown in approximately the order they will be done.

Note: If you are an enterprise level user with an urgent need for a particular feature, please contact sales@mysql.com to discuss sponsoring options. Targeted financing by sponsor companies allows us to allocate additional resources for specific purposes. One example of a feature sponsored in the past is replication.

1.6.1 New Features Planned for 4.1

The features below are not yet implemented in MySQL 4.1, but are planned for implementation before MySQL 4.1 moves into its beta phase. For a list what is already done in MySQL 4.1, see section Features Available in MySQL 4.1.

1.6.2 New Features Planned for 5.0

The following features are planned for inclusion into MySQL 5.0. Some of the features such as stored procedures are complete and are included in MySQL 5.0 alpha, which is available now. Others such as cursors are only partially available. Expect these and other features to mature and be fully supported in upcoming releases.

Note that because we have many developers that are working on different projects, there will also be many additional features. There is also a small chance that some of these features will be added to MySQL 4.1. For a list what is already done in MySQL 4.1, see section Features Available in MySQL 4.1.

For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See section 2.3.3 Installing from the Development Source Tree. As of December 2003, binary builds of version 5.0 are also available.

Stored Procedures
New functionality
Standards compliance, portability and migration
Speed enhancements
Usability enhancements

The news section of this manual includes a more in-depth list of features. See section C.1 Changes in release 5.0.x (Development).

1.6.3 New Features Planned for 5.1

New functionality
Speed enhancements
Usability enhancements

1.6.4 New Features Planned for the Near Future

New functionality
Standards compliance, portability and migration
Speed enhancements
Usability enhancements
New operating systems

1.6.5 New Features Planned for the Mid-Term Future

1.6.6 New Features We Don't Plan to Implement

We aim toward full compliance with SQL-92/SQL-99, so there are no features we plan not to implement.

1.7 MySQL Information Sources

1.7.1 MySQL Mailing Lists

This section introduces you to the MySQL mailing lists and provides some guidelines as to how the lists should be used. When you subscribe to a mailing list, you will receive all postings to the list as email messages. You can also to send your own questions and answers to the list. The MySQL Mailing Lists

To subscribe to or unsubscribe from any of the mailing lists described in this section, visit http://lists.mysql.com/. Please do not send messages about subscribing or unsubscribing to any of the mailing lists, because such messages are distributed automatically to thousands of other users.

Your local site may have many subscribers to a MySQL mailing list. If so, the site 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 MySQL mailing lists are as follows:

This list is for announcements of new versions of MySQL and related programs. This is a low-volume list to which all MySQL users should subscribe.
This is the main list for general MySQL discussion. Please note that some topics are better discussed on the more-specialized lists. If you post to the wrong list, you may not get an answer.
This is the mysql list in digest form. Subscribing to this list means you will get all list messages, sent as one large mail message once a day.
This list will be of interest to you if you want to stay informed about issues reported since the last release of MySQL or if you want to be actively involved in the process of bug hunting and fixing. See section How to Report Bugs or Problems.
This is the bugs list in digest form.
This list is for people who work on the MySQL code. This is also the forum for discussions on MySQL development and post patches.
This is the internals list in digest form.
This list is for people who work on the MySQL documentation: people from MySQL AB, translators, and other community members.
This is the mysqldoc list in digest form.
This list is for anyone interested in performance issues. Discussions concentrate on database performance (not limited to MySQL) but also include broader categories such as performance of the kernel, file system, disk system, and so on.
This is the benchmarks list in digest form.
This list is for discussions on packaging and distributing MySQL. This is the forum used by distribution maintainers to exchange ideas on packaging MySQL and on ensuring that MySQL looks and feels as similar as possible on all supported platforms and operating systems.
This is the packagers list in digest form.
This list is for discussions about the MySQL server and Java.It is mostly used to discuss JDBC drivers, including MySQL Connector/J.
This is the java list in digest form.
This list is for all topics concerning the MySQL software on Microsoft operating systems, such as Windows 9x/Me/NT/2000/XP.
This is the win32 list in digest form.
This list is for all topics concerning connecting to the MySQL server with ODBC.
This is the myodbc list in digest form.
This list is for all topics concerning the MySQL Control Center graphical client.
This is the mysqlcc list in digest form.
This list is for all topics concerning programming with the C++ API to MySQL.
This is the plusplus list in digest form.
This list is for all topics concerning the Perl support for MySQL with msql-mysql-modules, which is now named DBD::mysql.
This is the msql-mysql-modules list in digest form.

If you're unable to get an answer to your questions from a MySQL mailing list, one option is to purchase support from MySQL AB. This 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 lists in languages other than English. These lists are not operated by MySQL AB.

A French mailing list.
A Korean mailing list. Email subscribe mysql your@email.address to this list.
A German mailing list. Email subscribe mysql-de your@email.address to this list. You can find information about this mailing list at http://www.4t2.com/mysql/.
A Portuguese mailing list. Email subscribe mysql-br your@email.address to this list.
A Spanish mailing list. Email subscribe mysql your@email.address to this list. Asking Questions or Reporting Bugs

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, please follow the guidelines on sending mail to a MySQL mailing list, outlined in the next section, before contacting us. How to Report Bugs or Problems

The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log into the system, you will also be able to enter new reports.

Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug 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). mysqlbug can be found in the `scripts' directory (source distribution) and in the `bin' directory under your MySQL installation directory (binary distribution). If you are unable to use mysqlbug (for instance, if you are running on Windows), it is still vital that you include all the necessary information noted in this section (most importantly a description of the operating system and the MySQL version).

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.

Preferably, you should test the problem using the latest production or development version of MySQL Server before posting. Anyone should be able to repeat the bug by just using 'mysql test < script' on the included test case or by running the shell or Perl script that is included in the bug report.

All bugs posted in the bugs database at http://bugs.mysql.com/ will be corrected or documented in the next MySQL release. If only minor code changes are needed to correct a problem, we will also post a patch that fixes the problem.

If you have found a sensitive security bug in MySQL, please send an email to security@mysql.com.

If you have a repeatable bug report, please report it to the bugs database at http://bugs.mysql.com/. Note that even in this case it's good to run the mysqlbug script first to find information about your system. Any bug that we are able to repeat has a high chance of being fixed in the next MySQL release.

To report other problems, you can use one of the MySQL mailing lists.

Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often 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 faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.

The most common errors made in bug reports are (a) not including the version number of the MySQL distribution used and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and 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 already been fixed in newer MySQL versions. Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.

If you compiled MySQL from source, 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 your problem depends on your compiler, we need to know what compiler you use. Note that every compiling problem should be regarded as a bug and reported accordingly.

It is most helpful when a good description of the problem is included in the bug report. That is, give a good example of everything you did that led to the problem and describe, in exact detail, the problem itself. The best reports are those that include a full example showing how to reproduce the bug or problem. See section D.1.6 Making a Test Case If 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 Connector/ODBC (MyODBC), please try to generate a MyODBC trace file and send it with your report. See section 19.2.7 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 later in this section).

Please include the following information in your report:

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 19.2.4 How to Report Problems with MyODBC.

For solutions to some common problems, 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 summarize 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. Guidelines for Answering Questions on the Mailing List

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 summarize 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.

1.7.2 MySQL Community Support on IRC (Internet Relay Chat)

In addition to the various MySQL mailing lists, you can find experienced community people on IRC (Internet Relay Chat). These are the best networks/channels currently known to us:

If you are looking for IRC client software to connect to an IRC network, take a look at X-Chat (http://www.xchat.org/). X-Chat (GPL licensed) is available for Unix as well as for Windows platforms.

1.8 MySQL Standards Compliance

This section describes how MySQL relates to the ANSI/ISO SQL standards. MySQL Server has many extensions to the SQL standard, and here you will find out what they are and how to use them. You will also find information about functionality missing from MySQL Server, and how to work around some differences.

Our goal is to not restrict MySQL Server usability for any usage without a very good reason for doing so. Even if we don't have the resources to perform development for every possible use, we are always willing to help and offer suggestions to people who are trying to use MySQL Server in new territories.

One of our main goals with the product is to continue to work toward compliance with the SQL-99 standard, but without sacrificing speed or reliability. We are not afraid to add extensions to SQL or support for non-SQL features if this greatly increases the usability of MySQL Server for a large segment of our user base. (The new HANDLER interface in MySQL Server 4.0 is an example of this strategy. See section 13.1.3 HANDLER Syntax.)

We will continue to support transactional and non-transactional databases to satisfy both mission-critical 24/7 usage and heavy web/logging usage.

MySQL Server was designed from the start to work with medium size databases (10-100 million rows, or about 100 MB per table) on small computer systems. We will continue to extend MySQL Server to work even better with terabyte-size databases, as well as 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 the MySQL server makes development in both of these directions possible without any conflicts in the source tree.

We are currently not targeting realtime support, though you can already do a lot of things with our replication capabilities.

Database cluster support is planned to begin sometime in 2004 through implementation of a new storage engine.

We are looking at providing XML support in the database server.

1.8.1 What Standards MySQL Follows

Entry-level SQL-92. ODBC levels 0-3.51.

We are aiming toward supporting the full SQL-99 standard, but without making concessions to speed and quality of the code.

1.8.2 Selecting SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differentially for different clients. This allows applications to tailor server operation to their own requirements.

Modes define what SQL syntax MySQL should support and what kind of validation checks it should perform on the data. This makes it easier to use MySQL in a lot of different environments and to use MySQL together with other database servers.

You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option. Beginning with MySQL 4.1, you can also change the mode after startup time by setting the sql_mode variable with a SET [SESSION|GLOBAL] sql_mode='modes' statement.

For more information on setting the server mode, see section 5.2.2 The Server SQL Mode.

1.8.3 Running MySQL in ANSI Mode

You can tell mysqld to use the ANSI mode with the --ansi startup option. See section 5.2.1 mysqld Command-line Options.

Running the server in ANSI mode is the same as starting it with these options:


In MySQL 4.1, you can achieve the same effect with these two statements:

SET GLOBAL sql_mode =

See section 1.8.2 Selecting SQL Modes.

In MySQL 4.1.1, the sql_mode options shown can be also be set with:

SET GLOBAL sql_mode="ansi";

In this case, the value of the sql_mode variable will be set to all options that are relevant for ANSI mode. You can check the result by doing:

mysql> SET GLOBAL sql_mode="ansi";
mysql> SELECT @@GLOBAL.sql_mode;

1.8.4 MySQL Extensions to the SQL-92 Standard

MySQL Server 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 Server 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 '!' character, the syntax within the comment will be executed only if the MySQL version is equal to or newer than the specified version number:


This means that if you have Version 3.23.02 or newer, MySQL Server will use the TEMPORARY keyword.

The following descriptions list MySQL extensions, organized by category.

Organization of data on disk
MySQL Server maps each database to a directory under the MySQL data directory, and tables within a database to filenames in the database directory. This has a few implications:
General language syntax
SQL statement syntax
Column types
Functions and operators

For a prioritized list indicating when new extensions will be added to MySQL Server, you should consult the online MySQL TODO list at http://www.mysql.com/doc/en/TODO.html. That is the latest version of the TODO list in this manual. See section 1.6 MySQL and the Future (The TODO).

1.8.5 MySQL Differences Compared to SQL-92

We try to make MySQL Server follow the ANSI SQL standard (SQL-92/SQL-99) and the ODBC SQL standard, but MySQL Server performs operations differently in some cases: Subqueries

MySQL Version 4.1 supports subqueries and derived tables. A subquery is a SELECT statement nested within another statement. A derived table (an unnamed view) is a subquery in the FROM clause of another statement. See section 13.1.8 Subquery Syntax.

For MySQL versions older than 4.1, most subqueries can be rewritten using joins or other methods. See section Rewriting Subqueries for Earlier MySQL Versions for examples that show how to do this. SELECT INTO TABLE

MySQL Server doesn't support the Sybase SQL extension: SELECT ... INTO TABLE .... Instead, MySQL Server supports the SQL-99 syntax INSERT INTO ... SELECT ..., which is basically the same thing. See section 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.

From version 5.0, MySQL supports SELECT ... INTO with user variables. The same syntax may also be used inside stored procedures using cursors and local variables. See section SELECT ... INTO Statement. Transactions and Atomic Operations

MySQL Server (version 3.23-max and all versions 4.0 and above) supports transactions with the InnoDB and BDB transactional storage engines. InnoDB provides full ACID compliance. See section 14 MySQL Table Types.

The other non-transactional storage engines in MySQL Server (such as MyISAM) follow a different paradigm for data integrity called ``Atomic Operations.'' In transactional terms, MyISAM tables effectively always operate in AUTOCOMMIT=1 mode. Atomic operations often offer comparable integrity with higher performance.

With MySQL Server supporting both paradigms, you can decide whether your applications are best served by the speed of atomic operations or the use of transactional features. This choice can be made on a per-table basis.

As noted, the trade off for transactional vs. non-transactional table types lies mostly in performance. Transactional tables have significantly higher memory and diskspace requirements, and more CPU overhead. On the other hand, transactional table types such as InnoDB also offer many significant features. MySQL Server's modular design allows the concurrent use of different storage engines to suit different requirements and deliver optimum performance in all situations.

But how does one use the features of MySQL Server to maintain rigorous integrity even with the non-transactional MyISAM tables, and how do these features compare with the transactional table types?

  1. If your applications are written in a way that is dependent on being able to call ROLLBACK rather than COMMIT in critical situations, 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. If you use non-transactional tables, MySQL Server 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.
  2. More often than not, critical transactional updates can be rewritten to be atomic. Generally speaking, all integrity problems that transactions solve can be done with LOCK TABLES or atomic updates, ensuring that you never will get an automatic abort from the server, which is a common problem with transactional database systems.
  3. Even a transactional system can lose data if the server goes down. The difference between different systems lies in just how small the time-lap is where they could lose data. No system is 100% secure, only ``secure enough.'' Even Oracle, reputed to be the safest of transactional database systems, is reported to sometimes lose data in such situations. To be safe with MySQL Server, whether using transactional tables or not, you only need to have backups and have binary logging turned on. With this you can recover from any situation that you could with any other transactional database system. It is always good to have backups, independent of which database system you use.

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 Server offers transaction-level 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 obtain a READ LOCAL lock (as opposed to a write lock) for a table that allows concurrent inserts at the end of the table, reads are allowed, as are inserts by other clients. The new inserted records will not be seen by the client that has the read lock until it releases the lock. 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 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 Server also guarantees that there will not be any dirty reads.

Following are some techniques for working with non-transactional tables: Stored Procedures and Triggers

Stored procedures are implemented in MySQL version 5.0. See section 18 Stored Procedures and Functions.

Triggers are scheduled for implementation in MySQL version 5.1. A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you could set up a stored procedure that is triggered each time a record is deleted from a transactional table and that stored procedure automatically deletes the corresponding customer from a customer table when all their transactions are deleted. Foreign Keys

In MySQL Server 3.23.44 and up, the InnoDB storage engine supports checking of foreign key constraints, including CASCADE, ON DELETE, and ON UPDATE. See section FOREIGN KEY Constraints.

For storage engines other than InnoDB, MySQL Server parses the FOREIGN KEY syntax in CREATE TABLE statements, but does not use or store it. In the future, the implementation will be extended to store this information in the table specification file so that it may be retrieved by mysqldump and ODBC. At a later stage, foreign key constraints will be implemented for MyISAM tables as well.

Foreign key enforcement offers several benefits to database developers:

Do keep in mind that these benefits come at the cost of additional overhead for the database server to perform the necessary checks. Additional checking by the server affects performance, which for some applications may be sufficiently undesirable as to be avoided if possible. (Some major commercial applications have coded the foreign-key logic at the application level for this reason.)

MySQL gives database developers the choice of which approach to use. If you don't need foreign keys and want to avoid the overhead associated with enforcing referential integrity, you can choose another table type instead, such as MyISAM. (For example, the MyISAM storage engine offers very fast performance for applications that perform only INSERT and SELECT operations, because the inserts can be performed concurrently with retrievals. See section 7.3.2 Table Locking Issues.)

If you choose not to take advantage of referential integrity checks, keep the following considerations in mind:

Be aware that the use of foreign keys can in some instances lead to problems:

Note that foreign keys in SQL are used to check and enforce referential integrity, not to join tables. If you want to get results from multiple tables from a SELECT statement, you do this by performing a join between them:

SELECT * FROM table1,table2 WHERE table1.id = table2.id;

See section JOIN Syntax. See section 3.6.6 Using Foreign Keys.

The FOREIGN KEY syntax without ON DELETE ... is often used by ODBC applications to produce automatic WHERE clauses. Views

Views are currently being implemented, and will appear in the 5.0 or 5.1 version of MySQL Server. Unnamed views (derived tables, a subquery in the FROM clause of a SELECT) are already implemented in version 4.1.

Historically, MySQL Server has been most used in applications and on web systems where the application writer has full control over database usage. Usage has shifted over time, and so we find that an increasing number of users now regard views as an important feature.

Views are useful for allowing users to access a set of relations (tables) as if it were a single table, and limiting their access to just that. Views can also be used to restrict access to rows (a subset of a particular table). One does not require views to restrict access to columns, as MySQL Server has a sophisticated privilege system. See section 5.3 General Security Issues and the MySQL Access Privilege System.

Many DBMS don't allow updates to a view. Instead, you have to perform the updates on the individual tables. In designing an implementation of views, our goal, as much as is possible within the confines of SQL, is full compliance with ``Codd's Rule #6'' for relational database systems: All views that are theoretically updatable, should in practice also be updatable. `--' as the Start of a Comment

Some other SQL databases use `--' to start comments. MySQL Server uses `#' as the start comment character. You can also use the C comment style /* this is a comment */ with MySQL Server. See section 10.5 Comment Syntax.

MySQL Server Version 3.23.3 and above support the `--' comment style, provided the comment is followed by a space (or by a control character such as a newline). The requirement for a space is to prevent 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 a negative value such as -1:

UPDATE tbl_name SET credit=credit--1

credit--1 is a legal expression in SQL, but if -- is interpreted as the start of a comment, part of the expression is discarded. The result is a statement that has a completely different meaning than intended:

UPDATE tbl_name SET credit=credit

The statement produces no change in value at all! This illustrates that allowing comments to start with `--' can have serious consequences.

Using our implementation of this method of commenting in MySQL Server Version 3.23.3 and up, credit--1 is actually safe.

Another safe feature is that the mysql command-line client removes all lines that start with `--'.

The following information is relevant only if you are running a MySQL version earlier than 3.23.3:

If you have an SQL program in a text file that contains `--' comments, you should use the replace utility as follows to convert the comments to use `#' characters:

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

1.8.6 How MySQL Deals with Constraints

MySQL allows you to work with both transactional tables that allow rollback and non-transactional tables that do not, so constraint handling is a bit different in MySQL than in other databases.

We have to handle the case when you have updated a lot of rows in a non-transactional table that cannot roll back when an error occurs.

The basic philosophy is to try to give an error for anything that we can detect at compile time but try to recover from any errors we get at runtime. We do this in most cases, but not yet for all. See section 1.6.4 New Features Planned for the Near Future.

The options MySQL has when an error occurs are to stop the statement in the middle or to recover as well as possible from the problem and continue.

The following sections describe what happens for the different types of constraints. Constraint PRIMARY KEY / UNIQUE

Normally you will get an error when you try to INSERT or UPDATE a row that causes a primary key, unique key or foreign key violation. If you are using a transactional storage engine such as InnoDB, MySQL will automatically roll back the transaction. If you are using a non-transactional storage engine, MySQL will stop at the incorrect row and leave any remaining rows unprocessed.

To make life easier, MySQL supports an IGNORE keyword for most commands that can cause a key violation (such as INSERT IGNORE and UPDATE IGNORE). In this case, MySQL will ignore any key violation and continue with processing the next row. You can get information about what MySQL did with the mysql_info() API function. See section mysql_info(). In MySQL 4.1 and up, you also can use the SHOW WARNINGS statement. See section SHOW WARNINGS | ERRORS.

Note that for the moment only InnoDB tables support foreign keys. See section FOREIGN KEY Constraints. Foreign key support in MyISAM tables is scheduled for implementation in MySQL 5.1. Constraint NOT NULL and DEFAULT values

To be able to support easy handling of non-transactional tables all columns in MySQL have default values.

If you insert an ``incorrect'' value in a column, such as a NULL in a NOT NULL column or a too-large numerical value in a numerical column, MySQL sets the column to the ``best possible value'' instead of producing an error. For numerical values, this is either 0, the smallest possible value or the largest possible value. For strings, this is either the empty string or the longest possible string that can be in the column.

This means that if you try to store NULL into a column that doesn't take NULL values, MySQL Server instead stores 0 or '' (the empty string). This last behavior can, for single row inserts, be changed with the -DDONT_USE_DEFAULT_FIELDS compile option.) See section 2.3.2 Typical configure Options. This causes INSERT statements to generate an error unless you explicitly specify values for all columns that require a non-NULL value.

The reason for the preceding rules is that we can't check these conditions until the query has begun executing. We can't just roll back if we encounter a problem after updating a few rows, because the table type may not support rollback. The option of terminating the statement is not that good; in this 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.

This means that you should generally not use MySQL to check column content. Instead, the application should ensure that is passes only legal values to MySQL.

In MySQL 5.0, we plan to improve this by providing warnings when automatic column conversions occur, plus an option to let you roll back statements that attempt to perform a disallowed column value assignment, as long as the statement uses only transactional tables. Constraint ENUM and SET

In MySQL 4.x, ENUM is not a real constraint, but is a more efficient way to define columns that can only contain a given set of values. This is because of the same reasons NOT NULL is not honored. See section Constraint NOT NULL and DEFAULT values.

If you insert an incorrect value into an ENUM column, it will be set to the reserved enumeration value 0, which will be displayed as an empty string in string context. See section 11.3.3 The ENUM Type.

If you insert an incorrect value into a SET column, the incorrect value is ignored. For example, if the column can contain the values 'a', 'b', and 'c', an attempt to assign 'a,x,b,y' results in a value of 'a,b'. See section 11.3.4 The SET Type.

1.8.7 Known Errors and Design Deficiencies in MySQL Errors in 3.23 Fixed in a Later MySQL Version

The following known errors or bugs are not fixed in MySQL 3.23 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.'' Errors in 4.0 Fixed in a Later MySQL Version

The following known errors or bugs are not fixed in MySQL 4.0 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.'' Open Bugs / Design Deficiencies in MySQL

The following problems are known and fixing them is a high priority:

The following problems are known and will be fixed in due time:

The following are known bugs in earlier versions of MySQL:

For platform-specific bugs, see the sections about compiling and porting. See section 2.3 MySQL Installation Using a Source Distribution. See section D Porting to Other Systems.

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