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1 General Information

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1 General Information

The MySQL (TM) 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.gnu.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:

Important:

Reports of errors (often called bugs), as well as questions and comments, should be sent to the mailing list at [email protected]. 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 Server, you should send an e-mail to [email protected].

1.1 About This Manual

This is the MySQL reference manual; it documents MySQL Version 4.0.5. Being a reference manual, it does not provide general instruction on SQL or relational database concepts.

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 Texinfo, plain text, Info, HTML, PostScript, 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.

If you have a hard time finding information in the manual, you can try our searchable version 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 [email protected].

This manual was initially written by David Axmark and Michael (Monty) Widenius. It is currently maintained by Michael (Monty) Widenius, Arjen Lentz, and Paul DuBois. For other contributors, see section C Credits.

The copyright (2002) 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
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.''
`filename'
Constant-width font with surrounding quotes is used for filenames and pathnames. Example: ``The distribution is installed under the `/usr/local/' directory.''
`c'
Constant-width font with surrounding quotes is also used to indicate character sequences. Example: ``To specify a wildcard, use the `%' character.''
italic
Italic font is used for emphasis, like this.
boldface
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 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 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:

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}

1.2 What Is MySQL?

MySQL, the most popular Open Source SQL database, is developed, distributed and supported by MySQL AB. MySQL AB is a commercial company founded by the MySQL developers that builds its business providing services around the MySQL database. See section 1.3 What Is 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 plays 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 tables are linked by defined relations making it possible to combine data from several tables on request. The SQL part of ``MySQL'' stands for ``Structured Query Language''—the most common standardised language used to access databases.
MySQL software is Open Source.
Open Source means that it is possible for anyone to use and modify. Anybody can download the MySQL software from the Internet and use it without paying anything. Anybody so inclined can study the source code and change it to fit their needs. The MySQL software uses the GPL (GNU General Public License), http://www.gnu.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 to some other database managers on our benchmark page. See section 5.1.4 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
For advanced technical information, see section 6 MySQL Language Reference. 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 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 localised way.

1.2.1 History of MySQL

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.

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 MySQL 4.x In A Nutshell.

Internals and Portability
  • Written in C and C++. Tested with a broad range of different compilers.
  • Works on many different platforms. See section 2.2.2 Operating Systems Supported by MySQL.
  • Uses GNU Automake (1.4), Autoconf (Version 2.52 or newer), and Libtool for portability.
  • APIs for C, C++, Eiffel, Java, Perl, PHP, Python, Ruby, and Tcl. See section 8 MySQL APIs.
  • Fully multi-threaded using kernel threads. This means it can easily use multiple CPUs if available.
  • Very fast B-tree disk tables with index compression.
  • A very fast thread-based memory allocation system.
  • Very fast joins using an optimised one-sweep multi-join.
  • In-memory hash tables which are used as temporary tables.
  • SQL functions are implemented through a highly optimised class library and should be as fast as possible! Usually there isn't any memory allocation at all after query initialisation.
  • The MySQL code gets tested with Purify (a commercial memory leakage detector) as well as with Valgrind, a GPL tool (http://developer.kde.org/~sewardj/).
Column Types
  • Many column types: signed/unsigned integers 1, 2, 3, 4, and 8 bytes long, FLOAT, DOUBLE, CHAR, VARCHAR, TEXT, BLOB, DATE, TIME, DATETIME, TIMESTAMP, YEAR, SET, and ENUM types. See section 6.2 Column Types.
  • Fixed-length and variable-length records.
  • All columns have default values. You can use INSERT to insert a subset of a table's columns; those columns that are not explicitly given values are set to their default values.
Commands and Functions
  • Full operator and function support in the 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;
    
  • Full support for SQL GROUP BY and ORDER BY clauses. Support for group functions (COUNT(), COUNT(DISTINCT ...), AVG(), STD(), SUM(), MAX(), and MIN()).
  • Support for LEFT OUTER JOIN and RIGHT OUTER JOIN with ANSI SQL and ODBC syntax.
  • Aliases on tables and columns are allowed as in the SQL92 standard.
  • 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.
  • The MySQL-specific 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.
  • Function names do not clash with table or column names. For example, 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 6.1.7 Is MySQL Picky About Reserved Words?.
  • You can mix tables from different databases in the same query (as of Version 3.22).
Security
  • A privilege and password system that is very flexible and secure, and allows host-based verification. Passwords are secure because all password traffic is encrypted when you connect to a server.
Scalability and Limits
  • Handles large databases. We are using MySQL Server with some databases that contain 50 million records and we know of users that use MySQL Server with 60,000 tables and about 5,000,000,000 rows.
  • Up to 32 indexes per table are allowed. Each index may consist of 1 to 16 columns or parts of columns. The maximum index width is 500 bytes (this may be changed when compiling MySQL Server). An index may use a prefix of a CHAR or VARCHAR field.
Connectivity
  • Clients may connect to the MySQL server using TCP/IP Sockets, Unix Sockets (Unix), or Named Pipes (NT).
  • ODBC (Open-DataBase-Connectivity) support for Win32 (with source). All ODBC 2.5 functions and many others. For example, you can use MS Access to connect to your MySQL server. See section 8.3 MySQL ODBC Support.
Localisation
  • The server can provide error messages to clients in many languages. See section 4.6.2 Non-English Error Messages.
  • Full support for several different character sets, including ISO-8859-1 (Latin1), german, big5, ujis, and more. For example, the Scandinavian characters 'å', 'ä' and 'ö' are allowed in table and column names.
  • All data is saved in the chosen character set. All comparisons for normal string columns are case-insensitive.
  • Sorting is done according to the chosen character set (the Swedish way by default). It is possible to change this when the MySQL server is started. To see an example of very advanced sorting, look at the Czech sorting code. MySQL Server supports many different character sets that can be specified at compile and runtime.
Clients and Tools
  • Includes 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 Database Administration.
  • All MySQL programs can be invoked with the --help or -? options to obtain online assistance.

1.2.3 How Stable Is MySQL?

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.

Original code stems back from the early '80s, providing a stable code base, and the ISAM table format 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 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 the MySQL Server 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 Server. 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.

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 server clusters using replication are in production use, with good results. Work on enhanced replication features is continuing in MySQL 4.x.
InnoDB tables -- Stable (in 3.23 from 3.23.49)
The InnoDB transactional table handler has now 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 table handler interface in MySQL Server, so it will take some time before this is as well tested as the other table types.
FULLTEXT -- Beta
Full-text search works but is not yet widely used. Important enhancements are being implemented for MySQL 4.0.
MyODBC 2.50 (uses ODBC SDK 2.5) -- Gamma
Increasingly in wide 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 only regards the new code in the 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.
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 OS 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.

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.

1.2.4 How Big Can MySQL Tables Be?

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 (can be changed with flag)
Solaris 2.7 Intel 4G
Solaris 2.7 UltraSPARC 512G

On Linux 2.2 you can get bigger tables than 2G by using the LFS patch for the ext2 filesystem. On Linux 2.4 patches also exist for ReiserFS to get support for big files.

This means that the table size for MySQL databases 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.

1.2.5 Year 2000 Compliance

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

You may run into problems with applications that use MySQL Server 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 Server 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 Server is Y2K-compliant, it is your responsibility to provide unambiguous input. See section 6.2.2.1 Y2K Issues and Date Types for MySQL Server's rules for dealing with ambiguous date input data (data containing 2-digit year values).

1.3 What Is 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.

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 the MySQL software 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 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.

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.

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.

1.3.1.1 Support

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.

For more information and ordering support at various levels, see http://www.mysql.com/support/ or contact our sales staff at [email protected].

1.3.1.2 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 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 as a training partner, please visit the training section at http://www.mysql.com/training/ or contact us at: [email protected].

The MySQL Certification Program is being released in the second half of 2002. For details please see http://www.mysql.com/training/certification.html.

1.3.1.3 Consulting

MySQL AB and its Authorised 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, but 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 [email protected].

1.3.1.4 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 (like the requirement that your own application becomes GPL as well), you may purchase a commercial license for the same product from MySQL AB. See http://www.mysql.com/support/arrangements/price.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 table handler that offers ACID support, row-level locking, crash recovery, multi-versioning, foreign key support, and more. See section 7.5 InnoDB Tables.

1.3.1.5 Partnering

MySQL AB has a worldwide partner programme that covers training courses, consulting & 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 e-mail [email protected].

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.

1.3.1.6 Advertising

The MySQL web site (http://www.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 percent of our visitors authorise purchase decisions, and only nine percent 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://www.mysql.com/, please send an e-mail message to [email protected].

1.3.2 Contact Information

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

For press service and inquiries not covered in our News releases (http://www.mysql.com/news/), please send e-mail to [email protected].

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 website, see http://www.mysql.com/support/, or send an e-mail message to [email protected].

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 at [email protected]. See section 1.3.1.2 Training and Certification.

For information on the MySQL Certification Program, please see http://www.mysql.com/training/certification.html. See section 1.3.1.2 Training and Certification.

If you're interested in consulting, please visit the consulting section at http://www.mysql.com/consulting/. If you have restricted access to the Internet, please contact the MySQL AB consulting staff at [email protected]. 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. More information about licensing can be found at http://www.mysql.com/support/arrangements/price.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 an e-mail message to [email protected] (for licensing questions) or to [email protected] (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 e-mail to [email protected]. See section 1.3.1.5 Partnering.

If you are interested in placing a banner advertisement on the MySQL web site (http://www.mysql.com/), please send e-mail to [email protected]. See section 1.3.1.6 Advertising.

For more information on the MySQL trademark policy, refer to http://www.mysql.com/company/trademark.html or send e-mail to [email protected]. 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 an e-mail message to [email protected]. Please do not send your CV as an attachment, but rather as plain text at the end of your e-mail message.

For general discussion among 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 [email protected]. If you have found a sensitive security bug in the MySQL Server, please send an e-mail to [email protected]. 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 [email protected].

If you have any suggestions concerning additions or corrections to this manual, please send them to the manual team at [email protected].

For questions or comments about the workings or content of the MySQL web site (http://www.mysql.com/), please send e-mail to [email protected].

Questions about the MySQL Portals (http://www.mysql.com/portal/) may be sent to [email protected].

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 e-mail [email protected].

For all other inquires, please send e-mail to [email protected].

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 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 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 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 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, contact our sales staff at [email protected].

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 Server 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.

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 What Is 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 H GNU General Public License. The text of this license can also be found as the file `COPYING' in the distributions.
  2. The GNU getopt library is covered by the GNU Lesser General Public License. See section I GNU Lesser General Public License.
  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 more strict license (http://www.mysql.com/support/arrangements/mypl.html). See the documentation of the specific version for information.
  5. The manual is currently not distributed under a GPL-style license. Use of the manual is subject to the following terms:
    • Conversion to other formats is allowed, but the actual content may not be altered or edited in any way.
    • You may create a printed copy for your own personal use.
    • For all other uses, such as selling printed copies or using (parts of) the manual in another publication, prior written agreement from MySQL AB is required.
    Please e-mail [email protected] 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 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 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/support/arrangements.html for more information.

Older versions of MySQL (3.22 and earlier) are subject to a more strict license (http://www.mysql.com/support/arrangements/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.

1.4.3.1 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. Otherwise you break the license terms and forfeit your right to use the GPL program altogether and 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/support/arrangements/price.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 at [email protected].

1.4.3.2 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 more complete coverage of the common questions about the GPL see the generic FAQ from the Free Software Foundation at http://www.gnu.org/licenses/gpl-faq.html. Some common cases:

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.

1.4.4.1 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 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.

1.4.4.2 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:

Contact us at [email protected] to inquire about special arrangements to fit your needs.

1.4.4.3 When do you need a Written Permission to use MySQL Logos?

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.

1.4.4.4 MySQL AB Partnership Logos

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 section 1.3.1.5 Partnering.

1.4.4.5 Using the word MySQL in Printed Text or Presentations

MySQL 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, state that MySQL is a trademark of MySQL AB. Please refer to our trademark policy at http://www.mysql.com/company/trademark.html for details.

1.4.4.6 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 4.x In A Nutshell

Long promised by MySQL AB and long awaited by our users, MySQL Server 4.0 is now available in beta version for download from http://www.mysql.com/ and our mirrors.

Main 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.

1.5.1 Stepwise Rollout

The rollout of MySQL Server 4.x comes in several steps, with the first version labelled 4.0.0-alpha already containing most of the new features. Additional features have since been incorporated into MySQL 4.0.1, 4.0.2, and onward; MySQL 4.0.3 has been labelled beta. Further new features are being added in MySQL 4.1, targeted for alpha release in third quarter 2002.

1.5.2 Ready for Immediate Development Use

Users are not recommended to switch their production systems to a MySQL Server 4.x until it is released in beta version (such as 4.0.3 beta). 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 Server 4.x even in alpha form for development use, with the release schedule of MySQL Server 4.x being such that it will reach stable state before the deployment of user applications now under development.

1.5.3 Embedded MySQL

libmysqld makes MySQL Server suitable for a vastly expanded realm of applications. Using the embedded MySQL server library, one 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, etc.

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 8.4.9 libmysqld, the Embedded MySQL Server Library.

1.5.4 Other Features Available From MySQL 4.0

1.5.5 Future MySQL 4.x Features

For the upcoming MySQL Server 4.x releases, expect the following features now still under development:

1.5.6 MySQL 4.1, The Following Development Release

MySQL Server 4.0 lays the foundation for the new features of MySQL Server 4.1 and onward, 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 the MySQL Database Server 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 Server will then match the requirement checklist of very demanding buyers.

1.6 MySQL Information Sources

1.6.1 MySQL Portals

The MySQL Portals (http://www.mysql.com/portal/) represent the ultimate resource to find MySQL AB Partners, as well as books, or other MySQL-related solutions that you may be looking for. Items are categorised and rated in order to make it easy for you to locate information.

By registering as a user, you will have the ability to comment on and rate items presented in portals. You will also receive relevant newsletters according to your user profile that you may update at any time.

Some of the current MySQL Portal categories include:

Partners
Find MySQL AB partners worldwide.
Books
Comment on, vote for, and buy books related to MySQL.
Development
Various links to different sites that are using MySQL Server for different purposes, with a description of each site. This information can give you an idea of who uses the MySQL database software and how MySQL Server can fulfill requirements. Let us know about your site or success story, too! Visit http://www.mysql.com/feedback/testimonial.php.
Software
Find, buy, and download several applications and wrappers that make use of the MySQL server.
Distributions
From here you can find the various Linux distributions and other software packages that contain the MySQL software.
Service Providers
Companies providing MySQL-related services.

1.6.2 MySQL Mailing Lists

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 e-mail messages all other postings on the list, and you will be able to send in your own questions and answers.

1.6.2.1 The MySQL Mailing Lists

To subscribe to the main MySQL mailing list, send a message to the electronic mail address [email protected].

To unsubscribe from the main MySQL mailing list, send a message to the electronic mail address [email protected].

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, by 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 [email protected], send a message to [email protected].

Mail to [email protected] or [email protected] 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 [email protected]. However, please do not send mail about subscribing or unsubscribing to [email protected] because any mail sent to that address is distributed automatically to thousands of other users.

Your local site may have many subscribers to [email protected]. If so, it may have a local mailing list, so 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:

[email protected] announce
This is for announcement of new versions of MySQL and related programs. This is a low-volume list all MySQL users should subscribe to.
[email protected] mysql
The main list for general MySQL discussion. Please note that some topics are better discussed on the more-specialised lists. If you post to the wrong list, you may not get an answer!
[email protected] mysql-digest
The mysql list in digest form. That means you get all individual messages, sent as one large mail message once a day.
bugs-s[email protected] bugs
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 Server 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 only small code changes are needed, we will also post a patch that fixes the problem.
[email protected] bugs-digest
The bugs list in digest form.
[email protected] internals
A list for people who work on the MySQL code. On this list one can also discuss MySQL development and post patches.
[email protected] internals-digest
A digest version of the internals list.
[email protected] java
Discussion about the MySQL server and Java. Mostly about the JDBC drivers.
[email protected] java-digest
A digest version of the java list.
[email protected] win32
All things concerning the MySQL software on Microsoft operating systems such as Windows 9x/Me/NT/2000/XP.
[email protected] win32-digest
A digest version of the win32 list.
[email protected] myodbc
All things about connecting to the MySQL server with ODBC.
[email protected] myodbc-digest
A digest version of the myodbc list.
[email protected] mycc
All things about the MySQL MyCC graphical client.
[email protected] mycc-digest
A digest version of the mycc list.
[email protected] plusplus
All things concerning programming with the C++ API to MySQL.
[email protected] plusplus-digest
A digest version of the plusplus list.
[email protected] msql-mysql-modules
A list about the Perl support for MySQL with msql-mysql-modules.
[email protected] msql-mysql-modules-digest
A digest version of the msql-mysql-modules list.

You subscribe or unsubscribe to all lists in the same way as described previously. 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 [email protected] or [email protected].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 languages other than English. Note that these are not operated by MySQL AB, so we can't guarantee the quality on these.

[email protected] A French mailing list
[email protected] A Korean mailing list
E-mail subscribe mysql [email protected] to this list.
[email protected] A German mailing list
E-mail subscribe mysql-de [email protected] to this list. You can find information about this mailing list at http://www.4t2.com/mysql/.
[email protected] A Portugese mailing list
E-mail subscribe mysql-br [email protected] to this list.
[email protected] A Spanish mailing list
E-mail subscribe mysql [email protected] to this list.

1.6.2.2 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, go ahead and read the next section about how to send mail to [email protected].

1.6.2.3 How to Report Bugs or Problems

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 [email protected]. If you can make a test case that clearly demonstrates the bug, you should post it to the [email protected] 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 Server 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 only small code changes are needed 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 [email protected].

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 the MySQL server 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 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 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 [email protected] 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 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!

1.6.2.4 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 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!

1.7 How Standards-compatible Is MySQL?

This section describes how MySQL relates to the ANSI SQL standards. MySQL Server 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 Server, and how to work around some differences.

Our goal is to not, without a very good reason, restrict MySQL Server 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 who are trying to use MySQL Server in new territories.

One of our main goals with the product is to continue to work toward 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 increases the usability of MySQL Server for a big part of our users. (The new HANDLER interface in MySQL Server 4.0 is an example of this strategy. See section 6.4.2 HANDLER Syntax.)

We will continue to support transactional and non-transactional databases to satisfy both heavy web/logging usage and mission-critical 24/7 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 both of these directions possible without any conflicts in the source tree.

We are currently not targeting realtime 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 previously of not sacrificing speed or reliability in the server.

1.7.1 What Standards Does MySQL Follow?

Entry-level SQL92. ODBC levels 0-3.51.

We are aiming toward supporting the full ANSI SQL99 standard, but without concessions to speed and quality of the code.

1.7.2 Running MySQL in ANSI Mode

If you start mysqld with the --ansi option, the following behaviour of MySQL Server changes:

This is the same as using --sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES, IGNORE_SPACE,SERIALIZE,ONLY_FULL_GROUP_BY.

1.7.3 MySQL Extensions to ANSI SQL92

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 '!', the syntax will be executed only if the MySQL version is equal to or newer than the used version number:

CREATE /*!32302 TEMPORARY */ TABLE t (a int);

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

The following is a list of MySQL extensions:

1.7.4 MySQL Differences Compared to ANSI SQL92

We try to make MySQL Server follow the ANSI SQL standard and the ODBC SQL standard, but in some cases MySQL Server does things differently:

For a prioritised list indicating when new extensions will be added to MySQL Server, 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).

1.7.4.1 SubSELECTs

MySQL Server currently only supports nested queries of the form INSERT ... SELECT ... and REPLACE ... SELECT .... You can, however, use the function IN() in other contexts. Subselects are currently being implemented in the 4.1 development tree.

Meanwhile, you can often rewrite the query without a subselect:

SELECT * FROM table1 WHERE id IN (SELECT id FROM table2);

This can be rewritten 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 subselects). For this situation there are two options available until subqueries are supported by MySQL Server.

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 construct 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 Server 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.

1.7.4.2 SELECT INTO TABLE

MySQL Server doesn't yet support the Oracle SQL extension: SELECT ... INTO TABLE .... MySQL Server 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.

1.7.4.3 Transactions and Atomic Operations

MySQL Server 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 Server 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 Server supporting both paradigms, the user is able to decide if he needs the speed of atomic operations or if he need to use transactional features in his applications. This choice can be made on a per-table basis.

How does one use the features of MySQL Server to maintain rigorous integrity and how do these features compare with the transactional paradigm?

  1. In the transactional paradigm, if your applications are written in a way that is dependent on the calling of ROLLBACK instead of 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. 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, fatal 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 database, which is a common problem with transactional databases.
  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 databases, 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 the update logging turned on. With this you can recover from any situation that you could with any other transactional database. It is, of course, always good to have backups, independent of which database 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 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), 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 Server also guarantees that there will not be any dirty reads.

Following are some techniques for working with non-transactional tables:

1.7.4.4 Stored Procedures and Triggers

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 re-issuing 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 Server around version 5.0. We are also looking at triggers.

1.7.4.5 Foreign Keys

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 Server 3.23.44 and up, InnoDB tables support checking of foreign key constraints. See section 7.5 InnoDB Tables. For other table types, MySQL Server 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 Server, 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 Server 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:

1.7.4.6 Views

It is planned to implement views in MySQL Server around version 5.0.

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 Server is mostly used in applications and on web systems 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 Server to restrict access to columns, as MySQL Server has a very sophisticated privilege system. See section 4.2 General Security Issues and the MySQL Access Privilege System.

1.7.4.7 `--' as the Start of a Comment

Some other SQL databases use `--' to start comments. MySQL Server has `#' as the start comment character. You can also use the C comment style /* this is a comment */ with MySQL Server. See section 6.1.6 Comment Syntax.

MySQL Server Version 3.23.3 and above support 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 Server 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 relevant only if you are running a MySQL version earlier than 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

1.7.5 Known Errors and Design Deficiencies in MySQL

The following problems are known and have a very high priority to get fixed:

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.

1.8 MySQL and The Future (The TODO)

This section lists the features that we plan to implement in MySQL Server.

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 sacrificing the speed or compromising the code.

1.8.1 Things That Should be in 4.0

All done. We now only do bug fixes for MySQL 4.0. See section D.1 Changes in release 4.0.x (Beta). Development has shifted to 4.1

1.8.2 Things That Should be in 4.1

The following features are planned for inclusion into MySQL 4.1. 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 4.0. Some of the work on MySQL 4.1 is already in progress.

1.8.3 Things That Must be Done in the Near Future

1.8.4 Things That Have to be Done Sometime

Time is given according to amount of work, not real time.

1.8.5 Things We Don't Plan To Do

1.9 How MySQL Compares to Other Databases

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 server, DB/2 server, 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 [email protected].

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.

1.9.1 How MySQL Compares to mSQL

Performance
For a true comparison of speed, consult the growing MySQL benchmark suite. See section 5.1.4 The MySQL Benchmark Suite. Because there is no thread creation overhead, a small parser, few features, and simple security, mSQL should be quicker at:
  • Tests that perform repeated connects and disconnects, running a very simple query during each connection.
  • 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.)
Because these operations are so simple, it is hard to be better at them when you have a higher startup overhead. After the connection is established, MySQL Server should perform much better. On the other hand, MySQL Server is much faster than mSQL (and most other SQL implementations) on the following:
  • Complex SELECT operations.
  • Retrieving large results (MySQL Server has a better, faster, and safer protocol).
  • Tables with variable-length strings because MySQL Server has more efficient handling and can have indexes on VARCHAR columns.
  • Handling tables with many columns.
  • Handling tables with large record lengths.
  • SELECT with many expressions.
  • SELECT on large tables.
  • Handling many connections at the same time. MySQL Server is fully multi-threaded. Each connection has its own thread, which means that no thread has to wait for another (unless a thread is modifying a table another thread wants to access). In 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.
  • Joins. mSQL can become pathologically slow if you change the order of tables in a SELECT. In the benchmark suite, a time more than 15,000 times slower than MySQL Server 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.
  • Using TEXT or BLOB columns.
SQL Features
  • GROUP BY and HAVING. mSQL does not support GROUP BY at all. MySQL Server 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 Server can do calculations in an INSERT or UPDATE. For example:
    mysql> UPDATE SET x=x*10+y WHERE x<20;
    
  • Aliasing. MySQL Server has column aliasing.
  • Qualifying column names. In MySQL Server, if a column name is unique among the tables used in a query, you do not have to use the full qualifier.
  • SELECT with functions. MySQL Server has many functions (too many to list here; see section 6.3 Functions for Use in SELECT and WHERE Clauses).
Disk Space Efficiency
That is, how small can you make your tables? MySQL Server has very precise types, so you can create tables that take very little space. An example of a useful MySQL datatype is the MEDIUMINT that is 3 bytes long. If you have 100 million records, saving even 1 byte per record is very important. mSQL2 has a more limited set of column types, so it is more difficult to get small tables.
Stability
This is harder to judge objectively. For a discussion of MySQL Server stability, see section 1.2.3 How Stable Is MySQL?. We have no experience with mSQL stability, so we cannot say anything about that.
Price
Another important issue is the license. MySQL Server has a more flexible license than 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.
Perl Interfaces
MySQL Server has basically the same interfaces to Perl as mSQL with some added features.
JDBC (Java)
MySQL Server currently has a lot of different JDBC drivers:
  • The mm driver: a type 4 JDBC driver by Mark Matthews [email protected]. This is released under the LGPL.
  • The Resin driver: this is a commercial JDBC driver released under open source. http://www.caucho.com/projects/jdbc-mysql/index.xtp
  • The gwe driver: a Java interface by GWE technologies (not supported anymore).
  • The jms driver: an improved gwe driver by Xiaokun Kelvin ZHU [email protected] (not supported anymore).
  • The twz driver: a type 4 JDBC driver by Terrence W. Zellers [email protected]. This is commercial but is free for private and educational use (not supported anymore).
The recommended driver is the mm driver. The Resin driver may also be good (at least the benchmarks look good), but we haven't received that much information about this yet. We know that mSQL has a JDBC driver, but we have too little experience with it to compare.
Rate of Development
MySQL Server has a small core team of developers, but we are quite used to coding C and C++ very rapidly. Because threads, functions, 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.
Utility Programs
Both mSQL and MySQL Server have many interesting third-party tools. Because it is very easy to port upward (from mSQL to MySQL Server), almost all the interesting applications that are available for mSQL are also available for MySQL Server. MySQL Server comes with a simple msql2mysql program that fixes differences in spelling between mSQL and MySQL Server 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 Server usually requires only minor effort.

1.9.1.1 How to Convert mSQL Tools for MySQL

According 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:

  1. Run the shell script msql2mysql on the source. This requires the replace program, which is distributed with MySQL Server.
  2. Compile.
  3. Fix all compiler errors.

Differences between the mSQL C API and the MySQL C API are:

1.9.1.2 How mSQL and MySQL Client/Server Communications Protocols Differ

There 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 here:

1.9.1.3 How mSQL 2.0 SQL Syntax Differs from MySQL

Column types

MySQL Server
Has the following additional types (among others; see section 6.5.3 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.
MySQL Server also supports the following additional type attributes:
  • UNSIGNED option for integer and floating-point 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 in the following table:
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 Server
Indexes may be specified at table creation time with the CREATE TABLE statement.
mSQL
Indexes must be created after the table has been created, with separate CREATE INDEX statements.

To Insert a Unique Identifier into a Table

MySQL Server
Use AUTO_INCREMENT as a column type specifier. See section 8.4.3.126 mysql_insert_id().
mSQL
Create a SEQUENCE on a table and select the _seq column.

To Obtain a Unique Identifier for a Row

MySQL Server
Add a 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
Use the _rowid column. Observe that _rowid may change over time depending on many factors.

To Get the Time a Column Was Last Modified

MySQL Server
Add a 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
Use the _timestamp column.

NULL Value Comparisons

MySQL Server
MySQL Server follows ANSI SQL, and a comparison with NULL is always NULL.
mSQL
In 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 Server.

String Comparisons

MySQL Server
Normally, string comparisons are performed in case-independent fashion with the sort order determined by the current character set (ISO-8859-1 Latin1 by default). If you don't like this, declare your columns with the BINARY attribute, which causes comparisons to be done according to the ASCII order used on the MySQL server host.
mSQL
All string comparisons are performed in case-sensitive fashion with sorting in ASCII order.

Case-insensitive Searching

MySQL Server
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 wildcard character.
mSQL
Use CLIKE.

Handling of Trailing Spaces

MySQL Server
Strips all spaces at the end of CHAR and VARCHAR columns. Use a TEXT column if this behaviour is not desired.
mSQL
Retains trailing space.

WHERE Clauses

MySQL Server
MySQL correctly prioritises everything (AND is evaluated before OR). To get mSQL behaviour in MySQL Server, use parentheses (as shown in an example later in this section).
mSQL
Evaluates everything from left to right. This means that some logical calculations with more than three arguments cannot be expressed in any way. It also means you must change some queries when you upgrade to MySQL Server. You do this easily by adding parentheses. Suppose you have the following mSQL query:
mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4;
To make MySQL Server 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 Server
Has tables to store grant (permission) options per user, host, and database. See section 4.2.6 How the Privilege System Works.
mSQL
Has a file `mSQL.acl' in which you can grant read/write privileges for users.

1.9.2 How MySQL Compares to PostgreSQL

When 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 databases 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 although we know MySQL Server thoroughly, 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 Server are both widely used products, but with different design goals, even if we are both striving toward ANSI SQL compliancy. This means that for some applications MySQL Server 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 Server is probably your best choice. If you need some of the extra features that only PostgreSQL can offer, you should use PostgreSQL.

1.9.2.1 MySQL and PostgreSQL development strategies

When adding things to MySQL Server 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 thoroughly 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 Server and PostgreSQL is that nearly all of the code in the MySQL server is 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, the majority of which 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 aforementioned 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.

1.9.2.2 Featurewise Comparison of MySQL and PostgreSQL

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 their respective databases. This web page is, however, extremely useful when you want to ensure that your applications work with many different databases or when you want to convert your application from one database to another.

MySQL Server offers the following advantages over PostgreSQL:

Drawbacks with MySQL Server compared to PostgreSQL:

PostgreSQL currently offers the following advantages over MySQL Server:

Note that because we know the MySQL road map, we have included in the following table the version when MySQL Server should support this feature. Unfortunately we couldn't do this for previous comparisons, because we don't know the PostgreSQL roadmap.

Feature MySQL version
Subselects 4.1
Foreign keys 4.1 (3.23 with InnoDB)
Views 5.0
Stored procedures 5.0
Triggers 5.0
Unions 4.0
Full join 4.1
Constraints 4.1 or 5.0
Cursors 4.1 or 5.0
R-trees 4.1 (for MyISAM tables)
Inherited tables Not planned
Extensible type system Not planned

Other reasons someone may consider using PostgreSQL:

Drawbacks with PostgreSQL compared to MySQL Server:

For a complete list of drawbacks, you should also examine the first table in this section.

1.9.2.3 Benchmarking MySQL and PostgreSQL

The only Open Source benchmark that we know of that can be used to benchmark MySQL Server and PostgreSQL (and other databases) is our own. It can be found at http://www.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 the next PostgreSQL release. The details about the machine we run the benchmark on 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 as a single figure, things are even easier.

This would be like us measuring the speed of MySQL Server compared to PostgreSQL by looking at the summary time of the MySQL benchmarks on our web page. Based on this MySQL Server 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 Server 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 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 show 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 claim that PostgreSQL performs better than MySQL Server. 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 to 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 probably the worst benchmark we have ever seen anyone conduct. This was not only tuned to only test what PostgreSQL is absolutely best at, but it was also totally unfair to 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 here we will just briefly repeat some things that were wrong with it.

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 Server 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 Server 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. In any of these 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 change and the preceding benchmarks are not that relevant anymore. MySQL Server now has 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 Server. PostgreSQL has, of course, also got new features since the test was made. As these tests are not publicly available there is no way for us to know how the database would perform in the same tests today.

Conclusion:

The only benchmarks that exist today that anyone can download and run against MySQL Server and PostgreSQL are the MySQL benchmarks. We here at MySQL AB 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 one 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 show 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 Server under certain conditions. We would just like to see a fair test where PostgreSQL performs very well, so that we could get some friendly competition going!

For more information about our benchmark 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.


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