The MySQL (R) software delivers a very fast, multi-threaded,
multi-user, and robust SQL (Structured Query Language)
database server.
MySQL Server is intended for mission-critical, heavy-load
production systems as well as for embedding into mass-deployed software.
MySQL is a trademark of MySQL AB.
The MySQL software is Dual Licensed. Users can choose to
use the MySQL software as an Open Source/Free Software
product under the terms of the GNU General Public License
(http://www.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:
MySQL Database Server,
see section 1.3 What Is MySQL AB?.
MySQL Database Server,
see section 1.2.2 The Main Features of MySQL.
MySQL Database Software to new architectures
or operating systems, see section E Porting to Other Systems.
MySQL Database Server,
see section 3 Tutorial Introduction.
SQL and benchmarking information, see the
benchmarking directory (`sql-bench' in the distribution).
Important:
Reports of errors (often called bugs), as well as questions and comments, should be sent to the mailing list at mysql@lists.mysql.com. See section 1.7.1.3 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 (`/usr/bin' for the
MySQL-server RPM package).
If you have found a sensitive security bug in MySQL Server,
you should send an e-mail to security@mysql.com.
This is the MySQL reference manual; it documents MySQL
up to Version 4.1.1-alpha. Functional changes are always
indicated with reference to the version, so this manual is also suitable
if you are using an older version of the MySQL software
(such as 3.23 or 4.0-production).
There are also references for version 5.0 (development).
Being a reference manual, it does not provide general instruction on
SQL or relational database concepts.
As the MySQL Database Software is under constant development,
the manual is also updated frequently.
The most recent version of this manual is available at
http://www.mysql.com/documentation/ in many different formats,
including HTML, PDF, and Windows HLP versions.
The primary document is the Texinfo file.
The HTML version is produced automatically using a modified version of
texi2html.
The plain text and Info versions are produced with makeinfo.
The PostScript version is produced using texi2dvi and dvips.
The PDF version is produced with pdftex.
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 docs@mysql.com.
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 (2003) to this manual is owned by the Swedish company
MySQL AB. See section 1.4.2 Copyrights and Licenses Used by MySQL.
This manual uses certain typographical conventions:
constant
mysqladmin works, invoke it with the
--help option.''
When commands are shown that are meant to be executed by a particular
program, the program is indicated by a prompt shown before the command. For
example, shell> indicates a command that you execute from your login
shell, and mysql> indicates a command that you execute from the
mysql client program:
shell> type a shell command here mysql> type a mysql command here
Shell commands are shown using Bourne shell syntax. If you are using a
csh-style shell, you may need to issue commands slightly differently.
For example, the sequence to set an environment variable and run a command
looks like this in Bourne shell syntax:
shell> VARNAME=value some_command
For csh, you would execute the sequence like this:
shell> setenv VARNAME value shell> some_command
Database, table, and column names must often be substituted into commands. To
indicate that such substitution is necessary, this manual uses
db_name, tbl_name, and col_name. For example, you might
see a statement like this:
mysql> SELECT col_name FROM db_name.tbl_name;
This means that if you were to enter a similar statement, you would supply your own database, table, and column names, perhaps like this:
mysql> SELECT author_name FROM biblio_db.author_list;
SQL keywords are not case-sensitive and may be written in uppercase or lowercase. This manual uses uppercase.
In syntax descriptions, square brackets (`[' and `]') are used
to indicate optional words or clauses. For example, in the following
statement, IF EXISTS is optional:
DROP TABLE [IF EXISTS] tbl_name
When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (`|'). When one member from a set of choices may be chosen, the alternatives are listed within square brackets (`[' and `]'):
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
When one member from a set of choices must be chosen, the alternatives are listed within braces (`{' and `}'):
{DESCRIBE | DESC} tbl_name {col_name | wild}
MySQL, the most popular Open Source SQL database, is
developed, 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.
MySQL Server. Since computers are very good at handling large
amounts of data, database management systems play a central role in computing,
as stand-alone utilities or as parts of other applications.
SQL part of ``MySQL'' stands for ``Structured
Query Language''. SQL is the most common standardised language used to
access databases and is defined by the ANSI/ISO SQL Standard.(The SQL
standard has been evolving since 1986 and several versions exist. In this
manual, ''SQL-92'' refers to the standard released in 1992,
''SQL-99'' refers to the standard released in 1999, and
''SQL:2003'' refers to the version of the standard that is expected
to be released in mid-2003.We use the term ''the SQL standard'' to
mean the current version of the SQL Standard at any time.)
Open Source.
Open Source means that it is possible for anyone to use and modify the software.
Anybody can download the MySQL software from the Internet and use it
without paying anything. If you wish, you may study the source code
and change it to suit your needs. The MySQL software uses the
GPL (GNU General Public License),
http://www.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.
MySQL Database Server is very fast, reliable, and easy to use.
If that is what you are looking for, you should give it a try.
MySQL Server also has a practical set of features developed in
close cooperation with our users. You can find a performance comparison
of MySQL Server with other database managers on our benchmark page.
See section 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.
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.
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.
We started out with the intention of using mSQL to connect to our
tables using our own fast low-level (ISAM) routines. However, after some
testing we came to the conclusion that mSQL was not fast enough 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 clear. Our base
directory and a large number of our libraries and tools have had the prefix
``my'' for well over 10 years. However, co-founder Monty Widenius's daughter
(some years younger) is also named My. Which of the two gave its name to
MySQL is still a mystery, even for us.
The name of the MySQL Dolphin (our logo) is Sakila. Sakila was chosen
by the founders of MySQL AB from a huge list of names suggested by users
in our "Name the Dolphin" contest. The winning name was submitted by
Ambrose Twebaze, an open source software developer from Swaziland, Africa.
According to Ambrose, the name Sakila has its roots in SiSwati, the local
language of Swaziland. Sakila is also the name of a town in Arusha,
Tanzania, near Ambrose's country of origin, Uganda.
The following list describes some of the important characteristics
of the MySQL Database Software. See section 1.5 MySQL 4.0 In A Nutshell.
MySQL code gets tested with Purify
(a commercial memory leakage detector) as well as with Valgrind,
a GPL tool (http://developer.kde.org/~sewardj/).
FLOAT, DOUBLE, CHAR, VARCHAR,
TEXT, BLOB, DATE, TIME, DATETIME,
TIMESTAMP, YEAR, SET, and ENUM types.
See section 6.2 Column Types.
SELECT and WHERE
clauses of queries. For example:
mysql> SELECT CONCAT(first_name, " ", last_name)
-> FROM tbl_name
-> WHERE income/dependents > 10000 AND age > 30;
GROUP BY and
ORDER BY clauses. Support
for group functions (COUNT(),
COUNT(DISTINCT ...),
AVG(), STD(),
SUM(), MAX(), MIN(), and GROUP_CONCAT()).
LEFT OUTER JOIN and RIGHT OUTER JOIN with both standard
SQL and ODBC syntax.
DELETE, INSERT, REPLACE, and UPDATE return
the number of rows that were changed (affected). It is possible to return
the number of rows matched instead by setting a flag when connecting to the
server.
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.
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?.
MySQL Server with databases that
contain 50 million records. We also know of users that
use MySQL Server with 60,000 tables and about 5,000,000,000 rows.
MySQL Server).
An index may use a prefix of a CHAR or VARCHAR field.
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 are supported, as are many others. For example, you can use
MS Access to connect to your MySQL server. See section 9.2 MySQL ODBC Support.
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.
myisamchk, a very fast utility for table checking,
optimisation, and repair. All of the functionality of myisamchk
is also available through the SQL interface.
See section 4 Database Administration.
MySQL programs can be invoked with the --help or -?
options to obtain online assistance.
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,
our new users quickly found some pieces of ``untested code''. Each new release
since then has had fewer portability problems (even though each new release
has also had many new features).
Each release of the MySQL Server has been usable. Problems have occurred
only when users try code from the ``gray zones.'' Naturally, new users
don't know what the gray zones are; this section therefore attempts to
document those areas that are currently known.
The descriptions mostly deal with Version 3.23 and 4.0 of MySQL Server.
All known and reported bugs are fixed in the latest version, with the
exception of those listed in the bugs section, which are things that
are design-related. See section 1.8.6 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:
MySQL 4.x.
InnoDB tables -- Stable (in 3.23 from 3.23.49)
InnoDB transactional storage engine has been declared
stable in the MySQL 3.23 tree, starting from version 3.23.49.
InnoDB is being used in large, heavy-load production systems.
BDB tables -- Gamma
Berkeley DB code is very stable, but we are still improving
the BDB transactional storage engine interface in
MySQL Server, so it will take some time before this is as well
tested as the other table types.
FULLTEXT -- Beta
MySQL 4.0.
MyODBC 3.51 (uses ODBC SDK 3.51) -- Stable
MyISAM tables -- Gamma
MyISAM storage
engine that checks if the table was closed properly on open and
executes an automatic check/repair of the table if it wasn't.
MyISAM tables in MySQL 4.0 for faster
insert of many rows.
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,
and the MySQL mailing list usually provides answers to common
questions. Bugs are usually fixed right away with a patch; for serious
bugs, there is almost always a new release.
MySQL Version 3.22 had a 4 GB (4 gigabyte) limit on table size. With the
MyISAM table type in MySQL Version 3.23, the maximum table
size was 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 | 2 GB, 4GB or more, depends on Linux version |
| Linux-Alpha | 8 TB (?) |
| Solaris 2.5.1 | 2 GB (possible 4GB with patch) |
| Solaris 2.6 | 4 GB (can be changed with flag) |
| Solaris 2.7 Intel | 4 GB |
| Solaris 2.7 UltraSPARC | 512 GB |
On Linux 2.2 you can get tables larger than 2 GB in size by using the LFS patch for the ext2 filesystem. On Linux 2.4 patches also exist for ReiserFS to get support for big files.
In effect, then, the table size for MySQL databases is normally
limited by the operating system.
By default, MySQL tables have a maximum size of about 4 GB. You can
check the maximum table size for a table with the SHOW TABLE STATUS
command or with the myisamchk -dv table_name.
See section 4.5.7 SHOW Syntax.
If you need a table that will be larger than 4 GB in size (and your operating system supports
this), set the AVG_ROW_LENGTH and MAX_ROWS
parameters accordingly when you create your table. See section 6.5.3 CREATE TABLE Syntax. You can
also set these parameters later, with ALTER TABLE. See section 6.5.4 ALTER TABLE Syntax.
If your big table is a read-only table, you could use
myisampack to merge and compress many tables into 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 get around the operating system file limit for MyISAM data
files 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.
The MySQL Server itself has no problems with Year 2000 (Y2K)
compliance:
MySQL Server uses Unix time functions and has no problems with dates
until 2069. All 2-digit years are considered to be in the range
1970 to 2069, which means that if you store 01 in a
YEAR column, MySQL Server treats it as 2001.
MySQL date functions are stored in one file, `sql/time.cc',
and are coded very carefully to be year 2000-safe.
MySQL Version 3.22 and later, the YEAR column type
can store years 0 and 1901 to 2155 in one byte and
display them using two or four digits.
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 example shows that the DATE and DATETIME data types will not
give any problems with future dates (they handle dates until the year
9999).
The TIMESTAMP data type, which is used to store the current time, supports
values that range from 19700101000000 to 20300101000000 on 32-bit
machines (signed value). On 64-bit machines, TIMESTAMP handles values
up to 2106 (unsigned value).
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).
MySQL AB is the company of the MySQL founders and main
developers. MySQL AB was originally established in Sweden by
David Axmark, Allan Larsson, and Michael Monty Widenius.
The developers of the MySQL server are all employed by the company.
We are a virtual organisation with people in a dozen countries around
the world. We communicate extensively over the Net every day with one another
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:
Open Source philosophy and support the
Open Source community.
The MySQL web site (http://www.mysql.com/)
provides the latest information about MySQL and MySQL AB.
One of the most common questions we encounter is: ``How can you make a living from something you give away for free?'' This is how.
MySQL AB makes money on support, services, commercial licenses,
and royalties. We use these revenues to fund product development
and to expand the MySQL business.
The company has been profitable since its inception. In October 2001, we accepted venture financing from leading Scandinavian investors and a handful of business angels. This investment is used to solidify our business model and build a basis for sustainable growth.
MySQL AB is run and owned by the founders and main developers of
the MySQL database. The developers are committed to giving support
to customers and other users in order to stay in touch with their needs
and problems. All our support is given by qualified developers. Really
tricky questions are answered by Michael Monty Widenius, principal
author of the MySQL Server.
See section 1.4.1 Support Offered by MySQL AB.
For more information and ordering support at various levels, see http://www.mysql.com/support/ or contact our sales staff at sales@mysql.com.
MySQL AB delivers MySQL and related training worldwide.
We offer both open courses and in-house courses tailored to 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 used in our
documentation and our sample applications, and is always updated
to reflect the latest MySQL version. Our trainers are backed by
the development team to guarantee the quality of the training and the
continuous development of the course material. This also ensures
that no questions raised during the courses remain unanswered.
Attending our training courses will enable you to achieve your MySQL
application goals. You will also:
MySQL Certification.
If you are interested in our training as a potential participant or as a training partner, please visit the training section at http://www.mysql.com/training/ or contact us at: training@mysql.com.
For details about the MySQL Certification Program, please see
http://www.mysql.com/certification/.
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---it also extends into programming and scripting
languages such as PHP, Perl, and more.
If you are interested in our consulting services or want to become a consulting partner, please visit the consulting section of our web site at http://www.mysql.com/consulting/ or contact our consulting staff at consulting@mysql.com.
The MySQL database is released under the
GNU General Public License (GPL).
This means that the MySQL software can be used free of charge
under the GPL. If you do not want to be bound by the GPL
terms (such as the requirement that your application must also be GPL,
you may purchase a commercial license for the same product
from MySQL AB; see http://www.mysql.com/products/pricing.html.
Since MySQL AB owns the copyright to the MySQL source code,
we are able to employ Dual Licensing, which means that the same
product is available under GPL and under a commercial
license. This does not in any way affect the Open Source
commitment of MySQL AB. For details about when a commercial
license is required, please see section 1.4.3 MySQL Licenses.
We also sell commercial licenses of third-party Open Source GPL
software that adds value to MySQL Server. A good example is the
InnoDB transactional storage engine that offers ACID
support, row-level locking, crash recovery, multi-versioning, foreign
key support, and more. See section 7.5 InnoDB Tables.
MySQL AB has a worldwide partner programme that covers training
courses, consulting and support, publications, plus reselling and
distributing MySQL and related products. MySQL AB Partners
get visibility on the http://www.mysql.com/ web site and the right
to use special versions of the MySQL trademarks to identify their
products and promote their business.
If you are interested in becoming a MySQL AB Partner, please e-mail
partner@mysql.com.
The word MySQL and the MySQL dolphin logo are trademarks of
MySQL AB. See section 1.4.4 MySQL AB Logos and Trademarks.
These trademarks represent a significant value that the MySQL
founders have built over the years.
The MySQL web site (http://www.mysql.com/) is popular among
developers and users. In 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 purchases within the last half-year, and 70% plan
to make one in the next few months.
The MySQL web site (http://www.mysql.com/)
provides the latest information about MySQL and MySQL AB.
For press services and inquiries not covered in our News releases (http://www.mysql.com/news/), please send an e-mail to press@mysql.com.
If you have a valid support contract with MySQL AB, you will
get timely, precise answers to your technical questions about the
MySQL software. For more information, see section 1.4.1 Support Offered by MySQL AB.
On our web site, see http://www.mysql.com/support/, or send
an e-mail to sales@mysql.com.
For information about MySQL training, please visit the training
section at http://www.mysql.com/training/. If you have
restricted access to the Internet, please contact the MySQL AB
training staff via e-mail at training@mysql.com.
See section 1.3.1.2 Training and Certification.
For information on the MySQL Certification Program, please see
http://www.mysql.com/certification/.
See section 1.3.1.2 Training and Certification.
If you're interested in consulting, please visit the consulting
section of our web site at http://www.mysql.com/consulting/. If you have
restricted access to the Internet, please contact the MySQL AB
consulting staff via e-mail at consulting@mysql.com.
See section 1.3.1.3 Consulting.
Commercial licenses may be purchased online at
https://order.mysql.com/. There you will also find information
on how to fax your purchase order to MySQL AB. More information
about licensing can be found at
http://www.mysql.com/products/pricing.html.
If you have
questions regarding licensing or you want a quote for a high-volume
license deal, please fill in the contact form on our web site
(http://www.mysql.com/) or send an e-mail message
to licensing@mysql.com (for licensing questions) or to
sales@mysql.com (for sales inquiries).
See section 1.4.3 MySQL Licenses.
If you represent a business that is interested in partnering with
MySQL AB, please send an e-mail to partner@mysql.com.
See section 1.3.1.5 Partnering.
For more information on the MySQL trademark policy, refer to
http://www.mysql.com/company/trademark.html or send an e-mail to
trademark@mysql.com.
See section 1.4.4 MySQL AB Logos and Trademarks.
If you are interested in any of the MySQL AB jobs listed in our
jobs section (http://www.mysql.com/company/jobs/),
please send an e-mail to jobs@mysql.com.
Please do not send your CV as an attachment, but rather as plain text
at the end of your e-mail message.
For general discussion among our many users, please direct your attention to the appropriate mailing list. See section 1.7.1 MySQL Mailing Lists.
Reports of errors (often called bugs), as well as questions and
comments, should be sent to the mailing list at
mysql@lists.mysql.com. If you have found a sensitive
security bug in the MySQL Server, please send an e-mail
to security@mysql.com.
See section 1.7.1.3 How to Report Bugs or Problems.
If you have benchmark results that we can publish, please contact us via e-mail at benchmarks@mysql.com.
If you have suggestions concerning additions or corrections to this manual, please send them to the manual team via e-mail at docs@mysql.com.
For questions or comments about the workings or content of the
MySQL web site (http://www.mysql.com/),
please send an e-mail to webmaster@mysql.com.
MySQL AB has a privacy policy, which can be read at
http://www.mysql.com/company/privacy.html.
For any queries regarding this policy, please send an e-mail to
privacy@mysql.com.
For all other inquires, please send an e-mail to info@mysql.com.
This section describes MySQL support and licensing arrangements.
Technical support from MySQL AB means individualised answers
to your unique problems direct from the software engineers who code
the MySQL database engine.
We try to take a broad and inclusive view of technical support. Almost
any problem involving MySQL 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, and so on.
Our support covers only the MySQL server and our own utilities,
not third-party products that access the MySQL server, though we
try to help with these where we can.
Detailed information about our various support options is given at http://www.mysql.com/support/, where support contracts can also be ordered online. If you have restricted access to the Internet, please contact our sales staff via e-mail at sales@mysql.com.
Technical support is like life insurance. You can live happily
without it for years, but when your hour arrives it becomes
critically important, yet it's too late to buy it.
If you use MySQL Server for important applications and encounter
sudden difficulties, it may be too time consuming to figure out all the answers
yourself. You may need immediate access to the most experienced
MySQL troubleshooters available, those employed by MySQL AB.
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:
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 be found as the file `COPYING'
in the distribution.
GNU getopt library is covered by the
GNU Lesser General Public License.
See section I GNU Lesser General Public License.
regexp library) are covered
by a Berkeley-style copyright.
MySQL (3.22 and earlier) are subject to a
stricter license
(http://www.mysql.com/products/mypl.html).
See the documentation of the specific version for information.
MySQL reference manual is currently not distributed
under a GPL-style license. Use of the manual is subject to the
following terms:
MySQL AB is required.
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.
The MySQL software is released under the
GNU General Public License (GPL),
which is probably the best known Open Source license.
The formal terms of the GPL license can be found at
http://www.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/products/licensing.html for
more information.
Older versions of MySQL (3.22 and earlier) are subject to a
stricter license
(http://www.mysql.com/products/mypl.html).
See the documentation of the specific version for information.
Please note that the use of the MySQL software under commercial
license, GPL, or the old MySQL license does not
automatically give you the right to use MySQL AB trademarks.
See section 1.4.4 MySQL AB Logos and Trademarks.
The GPL license is contagious in the sense that when a program
is linked to a GPL program all the source code for all the parts
of the resulting product must also be released under the GPL.
If you do not follow this GPL requirement, you break the license
terms and forfeit your right to use the GPL program altogether.
You also risk damages.
You need a commercial license:
GPL code from the MySQL
software and don't want the resulting product to be licensed under GPL,
perhaps because you want to build a commercial product or keep the added
non-GPL code closed source for other reasons. When purchasing
commercial licenses, you are not using the MySQL software under
GPL even though it's the same code.
GPL application that only works with the
MySQL software and ship it with the MySQL software. This type
of solution is considered to be linking even if it's done over a network.
MySQL software without providing
the source code as required under the GPL license.
MySQL
database even if you don't formally need a commercial license.
Purchasing support directly from MySQL AB is another good way
of contributing to the development of the MySQL software, with
immediate advantages for you.
See section 1.4.1 Support Offered by MySQL AB.
If you require a license, you will need one for each installation of the
MySQL software. This covers any number of CPUs on a machine, and there
is no artificial limit on the number of clients that connect to the server
in any way.
For commercial licenses, please visit our website at http://www.mysql.com/products/licensing.html. For support contracts, see http://www.mysql.com/support/. If you have special needs or you have restricted access to the Internet, please contact our sales staff via e-mail at sales@mysql.com.
You can use the MySQL software for free under the GPL if
you adhere to the conditions of the GPL.
For additional details, including answers to common questions about the GPL,
see the generic FAQ from the Free Software Foundation at
http://www.gnu.org/licenses/gpl-faq.html.
Common uses of the GPL include:
MySQL
source code under the GPL with your product.
MySQL source code bundled with other
programs that are not linked to or dependent on the MySQL system
for their functionality even if you sell the distribution commercially.
This is called mere aggregation in the GPL license.
MySQL
system, you can use it for free.
MySQL servers for your customers.
We encourage people to use ISPs that have MySQL support,
as this will give them the confidence that their ISP will, in fact,
have the resources to solve any problems they may experience with
the MySQL installation. Even if an ISP does not have
a commercial license for MySQL Server, their customers
should at least be given read access to the source of the MySQL
installation so that the customers can verify that it is correctly patched.
MySQL database software in conjunction with a
web server, you do not need a commercial license (so long as it is not
a product you distribute). This is true even if you run a commercial
web server that uses MySQL Server, because you are not
distributing any part of the MySQL system. However, in this
case we would like you to purchase MySQL support because the
MySQL software is helping your enterprise.
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.)
Many users of the MySQL database want to display the
MySQL AB dolphin logo on their web sites, books, or
boxed products. We welcome and encourage this, although it should be
noted that the word MySQL and the MySQL dolphin logo
are trademarks of MySQL AB and may only be used as stated in
our trademark policy at
http://www.mysql.com/company/trademark.html.
The MySQL dolphin logo was designed by the Finnish advertising
agency Priority in 2001. The dolphin was chosen as a suitable symbol
for the MySQL database since it is a smart, fast, and lean animal,
effortlessly navigating oceans of data. We also happen to like dolphins.
The original MySQL logo may only be used by representatives of
MySQL AB and by those having a written agreement allowing them
to do so.
We have designed a set of special Conditional Use logos that may be
downloaded from our web site at
http://www.mysql.com/press/logos.html
and used on third-party web sites without written permission from
MySQL AB.
The use of these logos is not entirely unrestricted but, as the name
implies, subject to our trademark policy that is also available on our
web site. You should read through the trademark policy if you plan to
use them. The requirements are basically as follows:
MySQL AB, are the creator and
owner of the site that displays the MySQL trademark.
MySQL AB
or to the value of MySQL AB trademarks. We reserve the right to
revoke the right to use the MySQL AB trademark.
MySQL database under GPL in an
application, your application must be Open Source and must
be able to connect to a MySQL server.
Contact us via e-mail at trademark@mysql.com to inquire about special arrangements to fit your needs.
You need written permission from MySQL AB before using MySQL
logos in the following cases:
MySQL AB logo anywhere except on your web site.
MySQL AB logo except the Conditional Use
logos mentioned previously on web sites or elsewhere.
Due to legal and commercial reasons we monitor the use of MySQL
trademarks on products, books, and other items. We usually require a fee for
displaying MySQL AB logos on commercial products, since we think
it is reasonable that some of the revenue is returned to fund further
development of the MySQL database.
MySQL partnership logos may be used only by companies and persons
having a written partnership agreement with MySQL AB. Partnerships
include certification as a MySQL trainer or consultant.
For more information, please see section 1.3.1.5 Partnering.
MySQL in Printed Text or Presentations
MySQL AB welcomes references to the MySQL database, but
it should be noted that the word MySQL is a trademark of MySQL AB.
Because of this, you must append the trademark symbol (TM) to
the first or most prominent use of the word MySQL in a text and,
where appropriate, state that MySQL is a trademark of
MySQL AB. For more information, please refer to our trademark policy at
http://www.mysql.com/company/trademark.html.
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.
Long promised by MySQL AB and long awaited by our users,
MySQL Server 4.0 is now available in production version.
MySQL 4.0 is available for download from http://www.mysql.com/ and from our mirrors. MySQL 4.0 has been tested by a large number of users and is in production use at many large sites.
The major new features of MySQL Server 4.0 are geared toward our existing business and community users, enhancing the MySQL database software as the solution for mission-critical, heavy-load database systems. Other new features target the users of embedded databases.
MySQL Version 4.0.12 was declared stable for production use in March 2003. This means that, in future, only bug fixes will be done for the 4.0 release series and only critical bug fixes will be done for the older 3.23 series. See section 2.5.2 Upgrading From Version 3.23 to 4.0.
New features to the MySQL software are being added to MySQL 4.1
which is now also available (alpha version).
See section 1.6 MySQL 4.1 In A Nutshell.
INSERTs, searching on
packed indexes, creation of FULLTEXT indexes, and COUNT(DISTINCT).
InnoDB storage engine is now offered as a standard feature of the
MySQL server. This means full support for ACID transactions,
foreign keys with cascading UPDATE/DELETE, and row-level locking
are now standard features.
See section 7.5 InnoDB Tables.
FULLTEXT search properties of MySQL Server 4.0 enables
FULLTEXT indexing of large text masses with both binary
and natural-language searching logic. You can customise minimal word
length and define your own stop word lists in any human language,
enabling a new set of applications to be built on MySQL Server.
See section 6.8 MySQL Full-text Search.
TRUNCATE TABLE (as in Oracle) and IDENTITY
as a synonym for automatically incremented keys (as in Sybase).
UNION statement, a long-awaited standard SQL feature.
MySQL now
supports a new character set, latin1_de, which ensures that the
German sorting order sorts words with umlauts in the same order
as do German telephone books.
mysqld parameters (startup options) can now be set without taking
down the servers. This is a convenient feature for Database Administrators (DBAs).
See section 5.5.6 SET Syntax.
DELETE and UPDATE statements have been added..
symbolic linking to MyISAM at the table
level (and not just the database level as before) and for enabling
symlink handling by default on Windows.
SQL_CALC_FOUND_ROWS and FOUND_ROWS() are new functions that make it
possible to find out the number of rows a SELECT query that includes a
LIMIT clause would have returned without that clause.
The news section of this manual includes a more in-depth list of features. See section D.3 Changes in release 4.0.x (Production).
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, and so on.
Many users of libmysqld will benefit from the MySQL
Dual Licensing. For those not wishing to be bound by the GPL,
the software is also made available under a commercial license.
The embedded MySQL library uses the same interface as the normal
client library, so it is convenient and easy to use. See section 9.1.15 libmysqld, the Embedded MySQL Server Library.
MySQL Server 4.0 laid the foundation for new features such as nested subqueries and Unicode (implemented in version 4.1) and for the work on SQL-99 stored procedures being done for version 5.0. These features come at the top of the wish list of many of our customers.
With these additions, critics of the MySQL Database Server have to be more imaginative than ever in pointing out deficiencies in the MySQL Database Management System. Already well-known for its stability, speed, and ease of use, MySQL Server will be able to fulfill the requirement checklists of very demanding buyers.
The features listed in this section are implemented in MySQL 4.1. Few other features are still planned for MySQL 4.1. See section 1.9.1 New Features Planned For 4.1.
Most new features being coded, such as stored procedures, will be available in MySQL 5.0. See section 1.9.2 New Features Planned For 5.0.
SELECT * FROM t1 WHERE t1.a=(SELECT t2.b FROM t2); SELECT * FROM t1 WHERE (1,2,3) IN (SELECT a,b,c FROM t2);
FROM clause of a SELECT statement. Here is
an example:
SELECT t1.a FROM t1, (SELECT * FROM t2) t3 WHERE t1.a=t3.a;
BTREE indexing is now supported for HEAP tables,
significantly improving response time for non-exact searches.
CREATE TABLE table LIKE table allows you to create a new table
with the exact structure of an existing table, using a single command.
SHOW WARNINGS shows warnings for the last command.
See section 4.5.7.9 SHOW WARNINGS | ERRORS.
HELP command that can be used in the mysql command line
client (and other clients) to get help for SQL commands.
The advantage of having this information on the server side is that the
information is always applicable for that particular server version.
INSERT ... ON DUPLICATE KEY UPDATE ... syntax has been
implemented. This allows you to UPDATE an existing row if the
INSERT would have caused a duplicate in a PRIMARY or
UNIQUE key (index).
See section 6.4.3 INSERT Syntax.
GROUP_CONCAT(),
adding the extremely useful capability of concatenating columns from
grouped rows into a single result string.
See section 6.3.7 Functions and Modifiers for Use with GROUP BY Clauses.
The news section in this manual includes a more in-depth list of features. See section D.2 Changes in release 4.1.x (Alpha).
New features are being added to MySQL 4.1, which is already available for download (alpha version). See section 1.6.3 Ready for Immediate Development Use.
The set of features that are being added to version 4.1 is mostly fixed. Additional development is already ongoing for version 5.0. MySQL 4.1 will go through the steps of Alpha (during which time new features might still be added/changed), Beta (when we have feature freeze and only bug corrections will be done), and Gamma (indicating that a production release is just weeks ahead). At the end of this process, MySQL 4.1 will become the new production release.
MySQL 4.1 is currently in the alpha stage, and binaries are available for download at http://www.mysql.com/downloads/mysql-4.1.html. All binary releases pass our extensive test suite without any errors on the platforms on which we test. See section D.2 Changes in release 4.1.x (Alpha).
New development for MySQL is focused on the 5.0 release, featuring Stored Procedures and other new features. See section 1.9.2 New Features Planned For 5.0.
For those wishing to take a look at the bleeding edge of MySQL development, we have already made our BitKeeper repository for MySQL version 5.0 publically available. See section 2.3.4 Installing from the Development Source Tree.
This section introduces you to the MySQL mailing lists and gives some guidelines as to how the lists should be used. When you subscribe to a mailing list, you will receive, as e-mail messages, all postings to the list. You will also be able to send your own questions and answers to the list.
To subscribe to the main MySQL mailing list, send a message to the electronic mail address mysql-subscribe@lists.mysql.com.
To unsubscribe from the main MySQL mailing list, send a message to the electronic mail address mysql-unsubscribe@lists.mysql.com.
When subscribing and unsubscribing, only the address to which you send your message 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
your_name@host.domain, send a message to
mysql-subscribe-your_name=host.domain@lists.mysql.com.
Mail to mysql-subscribe@lists.mysql.com or mysql-unsubscribe@lists.mysql.com is handled automatically by the ezmlm mailing list processor. Information about ezmlm is available at the ezmlm web site (http://www.ezmlm.org/).
To post a message to the list itself, send your message to
mysql@lists.mysql.com. Please do not send mail about
subscribing or unsubscribing to mysql@lists.mysql.com because all
mail sent to that address is distributed automatically to thousands of other
users.
Your local site may have many subscribers to mysql@lists.mysql.com.
If so, it may have a local mailing list, so that messages sent from
lists.mysql.com to your site are propagated to the local list. In such
cases, please contact your system administrator to be added to or dropped
from the local MySQL list.
If you wish to have traffic for a mailing list go to a separate mailbox in
your mail program, set up a filter based on the message headers. You can
use either the List-ID: or Delivered-To: headers to identify
list messages.
The MySQL mailing lists are as follows:
announce-subscribe@lists.mysql.com announce
mysql-subscribe@lists.mysql.com mysql
mysql-digest-subscribe@lists.mysql.com mysql-digest
mysql list in digest form. Subscribing to this list means
you will get all list messages, sent as one large mail message once a day.
bugs-subscribe@lists.mysql.com bugs
MySQL or if you want to be
actively involved in the process of bug hunting and fixing.
See section 1.7.1.3 How to Report Bugs or Problems.
bugs-digest-subscribe@lists.mysql.com bugs-digest
bugs list in digest form.
internals-subscribe@lists.mysql.com internals
internals-digest-subscribe@lists.mysql.com internals-digest
internals list in digest form.
mysqldoc-subscribe@lists.mysql.com mysqldoc
mysqldoc-digest-subscribe@lists.mysql.com mysqldoc-digest
mysqldoc list in digest form.
benchmarks-subscribe@lists.mysql.com benchmarks
benchmarks-digest-subscribe@lists.mysql.com benchmarks-digest
benchmarks list in digest form.
packagers-subscribe@lists.mysql.com packagers
packagers-digest-subscribe@lists.mysql.com packagers-digest
packagers list in digest form.
java-subscribe@lists.mysql.com java
java-digest-subscribe@lists.mysql.com java-digest
java list in digest form.
win32-subscribe@lists.mysql.com win32
win32-digest-subscribe@lists.mysql.com win32-digest
win32 list in digest form.
myodbc-subscribe@lists.mysql.com myodbc
myodbc-digest-subscribe@lists.mysql.com myodbc-digest
myodbc list in digest form.
mysqlcc-subscribe@lists.mysql.com mysqlcc
MySQL Control Center graphical client.
mysqlcc-digest-subscribe@lists.mysql.com mysqlcc-digest
mysqlcc list in digest form.
plusplus-subscribe@lists.mysql.com plusplus
plusplus-digest-subscribe@lists.mysql.com plusplus-digest
plusplus list in digest form.
msql-mysql-modules-subscribe@lists.mysql.com msql-mysql-modules
msql-mysql-modules,
which is now named DBD-mysql.
msql-mysql-modules-digest-subscribe@lists.mysql.com msql-mysql-modules-digest
msql-mysql-modules list in digest form.
You subscribe or unsubscribe to all lists using the same method described at the
beginning of this section. For example, to subscribe to or
unsubscribe from the myodbc list, send a message to
myodbc-subscribe@lists.mysql.com or
myodbc-unsubscribe@lists.mysql.com.
If you're unable to get an answer to your question(s) from a MySQL mailing list, one
option is to pay for support from MySQL AB. This will put you
in direct contact with MySQL developers. See section 1.4.1 Support Offered by MySQL AB.
The following table shows some MySQL mailing lists in languages other than English. These lists are not operated by MySQL AB, so we can't guarantee their quality.
mysql-france-subscribe@yahoogroups.com A French mailing list
list@tinc.net A Korean mailing list
subscribe mysql your@e-mail.address to this list.
mysql-de-request@lists.4t2.com A German mailing list
subscribe mysql-de your@e-mail.address to this list.
You can find information about this mailing list at
http://www.4t2.com/mysql/.
mysql-br-request@listas.linkway.com.br A Portuguese mailing list
subscribe mysql-br your@e-mail.address to this list.
mysql-alta@elistas.net A Spanish mailing list
subscribe mysql your@e-mail.address to this list.
Before posting a bug report or question, please do the following:
If you can't find an answer in the manual or the archives, check with your local MySQL expert. If you still can't find an answer to your question, please follow the guidelines on sending mail to mysql@lists.mysql.com, outlined in the next section, before contacting us.
Our bugs database is public, and can be browsed and searched by anyone at http://bugs.mysql.com/. If you log into the system, you will also be able to enter new reports.
Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug in the next release. This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.
We encourage everyone to use the mysqlbug script to generate a bug
report (or a report about any problem). mysqlbug can be
found in the `scripts' directory (source distribution) and in the
`bin' directory under your MySQL installation directory (binary distribution).
If you are unable to use mysqlbug (for instance, if you are running
on Windows), it is still vital that you include all the necessary information
noted in this section (most importantly a description of the operating system
and the MySQL version).
The mysqlbug script helps you generate a report by determining much
of the following information automatically, but if something important is
missing, please include it with your message. Please read this section
carefully and make sure that all the information described here is included
in your report.
Preferably, you should test the problem using the latest production or
development version of MySQL Server before posting. Anyone should be
able to repeat the bug by just using 'mysql test < script' on the
included test case or run the shell or Perl script that is included in the
bug report.
All bugs posted in the bugs database or on the bugs@lists.mysql.com list will be corrected or documented in the next MySQL release. If only minor code changes are needed to correct a problem, we will also post a patch that fixes the problem.
The normal place to report bugs is http://bugs.mysql.com/.
If you have found a sensitive security bug in MySQL, please send an e-mail to security@mysql.com.
If you have a repeatable bug report, please report this into the bugs
database at http://bugs.mysql.com/. Note that even in this case
it's good to run the mysqlbug script first to find information
about your system. Any bug that we are able to repeat has a high chance
of being fixed in the next MySQL release.
To report other problem, you can use mysql@lists.mysql.com.
Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is: if you are in doubt about stating something, state it. It is 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 made in bug reports are (a) not including the version number of the MySQL distribution used and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and version number). This is highly relevant information, and in 99 cases out of 100 the bug report is useless without it. Very often we get questions like, ``Why doesn't this work for me?'' Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has already been fixed in newer MySQL versions. Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.
Remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is MySQL-related. Most compilers are under development all the time and become better version by version. To determine whether your problem depends on your compiler, we need to know what compiler you use. Note that every compiling problem should be regarded as a bug and reported accordingly.
It is most helpful when a good description of the problem is included in the bug report. That is, give a good example of all the things you did that led to the problem and describe, in exact detail, the problem itself. The best reports are those that include a full example showing how to reproduce the bug or problem. See section E.1.6 Making a Test Case If You Experience Table Corruption.
If a program produces an error message, it is very important to include the message in your report. If we try to search for something from the archives using programs, it is better that the error message reported exactly matches the one that the program produces. (Even the case should be observed.) You should never try to remember what the error message was; instead, copy and paste the entire message into your report.
If you have a problem with MyODBC, please try to generate a MyODBC trace file and send it with your report. See section 9.2.7 Reporting Problems with MyODBC.
Please remember that many of the people who will read your report will
do so using an 80-column display. When generating reports or examples
using the mysql command-line tool, you should therefore use
the --vertical option (or the \G statement terminator)
for output that would exceed the available width for such a display
(for example, with the EXPLAIN SELECT statement; see the
example later in this section).
Please include the following information in your report:
mysqladmin version. mysqladmin can be
found in the `bin' directory under your MySQL installation
directory.
uname -a. If
you work with Windows, you can usually get the name and version number
by double-clicking your ''My Computer'' icon and pulling down the ''Help/About Windows''
menu.
mysqld died, you should also report the query that crashed
mysqld. You can usually find this out by running mysqld with
logging enabled. See section E.1.5 Using Log Files to Find Cause of Errors in mysqld.
mysqldump --no-data db_name tbl_name1 tbl_name2 .... This is very easy
to do and is a powerful way to get information about any table in a database.
The information will help us create a situation matching the one you have.
SELECT statements, you
should always include the output of EXPLAIN SELECT ..., and at
least the number of rows that the SELECT statement produces. You
should also include the output from SHOW CREATE TABLE tbl_name
for each involved table. The more information you give about your
situation, the more likely it is that someone can help you. The following
is an example of a very good bug report (it
should of course be posted with the mysqlbug script).
Example run using the mysql command-line tool (note the use of the
\G statement terminator for statements whose output width would
otherwise exceed that of an 80-column display device):
mysql> SHOW VARIABLES;
mysql> SHOW COLUMNS FROM ...\G
<output from SHOW COLUMNS>
mysql> EXPLAIN SELECT ...\G
<output from EXPLAIN>
mysql> FLUSH STATUS;
mysql> SELECT ...;
<A short version of the output from SELECT,
including the time taken to run the query>
mysql> SHOW STATUS;
<output from SHOW STATUS>
mysqld, try to provide an
input script that will reproduce the anomaly. This script should include any
necessary source files. The more closely the script can reproduce your
situation, the better. If you can make a reproducible test case, you should
post it on http://bugs.mysql.com/ for high-priority treatment.
If you can't provide a script, you should at least include the output
from mysqladmin variables extended-status processlist in your mail to
provide some information on how your system is performing.
mysqldump and create a `README' file
that describes your problem.
Create a compressed archive of your files using
tar and gzip or zip, and use ftp to transfer the
archive to ftp://support.mysql.com/pub/mysql/secret/. Then enter
the problem into our bugs database at http://bugs.mysql.com/.
ftp to transfer it to
ftp://support.mysql.com/pub/mysql/secret/. If the data is really top
secret and you don't want to show it even to us, then go ahead and provide
an example using other names, but please regard this as the last choice.
mysqld
daemon as well as the options that you use to run any MySQL client programs. The
options to programs like mysqld and mysql, and to the
configure script, are often keys to answers and are very relevant.
It is never a bad idea to include them. If you use any modules, such
as Perl or PHP, please include the version number(s) of those as well.
mysqlaccess, the output of mysqladmin reload, and all
the error messages you get when trying to connect. When you test your
privileges, you should first run mysqlaccess. After this, execute
mysqladmin reload version and try to connect with the program that
gives you trouble. mysqlaccess can be found in the `bin'
directory under your MySQL installation directory.
parse error, please check your syntax closely. If
you can't find something wrong with it, it's extremely likely that your
current version of MySQL Server doesn't support the syntax you are
using. If you are using the current version and the manual at
http://www.mysql.com/doc/ doesn't cover the
syntax you are using, MySQL Server doesn't support your query. In this
case, your only options are to implement the syntax yourself or e-mail
licensing@mysql.com and ask for an offer to implement it.
If the manual covers the syntax you are using, but you have an older version
of MySQL Server, you should check the MySQL change history to see
when the syntax was implemented. In this case, you have the option of
upgrading to a newer version of MySQL Server. See section D MySQL Change History.
myisamchk or CHECK TABLE and
REPAIR TABLE. See section 4 Database Administration.
mysqld should never crash a table if nothing killed it in the
middle of an update. If you can find the cause of mysqld dying,
it's much easier for us to provide you with a fix for the problem.
See section A.1 How to Determine What Is Causing Problems.
If you are a support customer, please cross-post the bug report to mysql-support@mysql.com for higher-priority treatment, as well as to the appropriate mailing list to see if someone else has experienced (and perhaps solved) the problem.
For information on reporting bugs in MyODBC, see section 9.2.4 How to Report Problems with MyODBC.
For solutions to some common problems, see section A Problems and Common Errors.
When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarise the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem.
If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer.
Try to summarise the essential part of the question in your reply; don't feel obliged to quote the entire original message.
Please don't post mail messages from your browser with HTML mode turned on. Many users don't read mail with a browser.
In addition to the various MySQL mailing lists, you can find experienced
community people on IRC (Internet Relay Chat).
These are the best networks/channels currently known to us:
#mysql
Primarily MySQL questions but other database and SQL questions welcome.
#mysqlphp
Questions about MySQL+PHP, a popular combination.
#mysqlperl
Questions about MySQL+Perl, another popular combination.
#mysql
MySQL questions.
If you are looking for IRC client software to connect to an IRC network,
take a look at X-Chat (http://www.xchat.org/).
X-Chat (GPL licensed) is available for Unix as well as for Windows platforms.
This section describes how MySQL relates to the ANSI/ISO SQL standards. MySQL Server has many extensions to the SQL standard, and here you will find out what they are and how to use them. You will also find information about functionality missing from MySQL Server, and how to work around some differences.
Our goal is to not, 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
compliance with the SQL-99 standard, but without sacrificing speed or reliability.
We are not afraid to add extensions to SQL or support for non-SQL
features if this greatly increases the usability of MySQL Server for a 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.
Entry-level SQL-92. ODBC levels 0-3.51.
We are aiming toward supporting the full SQL-99 standard, but without concessions to speed and quality of the code.
If you start mysqld with the --ansi option, the following
behaviour of MySQL Server changes:
|| is string concatenation instead of OR.
mysql.user table, you have to quote it:
SELECT "user" FROM mysql."user";
REAL will be a synonym for FLOAT instead of a synonym for
DOUBLE.
SERIALIZABLE.
See section 6.7.3 SET TRANSACTION Syntax.
GROUP BY that is not in the
field list.
This is the same as starting mysqld with:
--sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,
IGNORE_SPACE,ONLY_FULL_GROUP_BY --transaction-isolation=serializable
or in MySQL 4.1
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; SET sql_mode="REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY";
In MySQL 4.1.1 the sql_mode options shown can be also be set with:
SET sql_mode="ansi";
In this case, the sql_mode variable value will be set to all options
that are relevant for the ANSI mode. You can check the result by
doing:
mysql> SET sql_mode="ansi";
mysql> SELECT @@sql_mode;
-> "REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY,ANSI"
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:
MEDIUMINT, SET, ENUM, and the
different BLOB and TEXT types.
AUTO_INCREMENT, BINARY, NULL,
UNSIGNED, and ZEROFILL.
BINARY attribute or use the BINARY cast, which causes
comparisons to be done according to the ASCII order used on the
MySQL server host.
db_name.tbl_name syntax. Some SQL servers provide
the same functionality but call this User space.
MySQL Server doesn't support tablespaces as in:
create table ralph.my_table...IN my_tablespace.
LIKE is allowed on numeric columns.
INTO OUTFILE and STRAIGHT_JOIN in a SELECT
statement. See section 6.4.1 SELECT Syntax.
SQL_SMALL_RESULT option in a SELECT statement.
EXPLAIN SELECT to get a description of how tables are joined.
INDEX or KEY in a CREATE TABLE
statement. See section 6.5.3 CREATE TABLE Syntax.
TEMPORARY or IF NOT EXISTS with CREATE TABLE.
COUNT(DISTINCT list) where list has more than one element.
CHANGE col_name, DROP col_name, or DROP
INDEX, IGNORE or RENAME in an ALTER TABLE
statement. See section 6.5.4 ALTER TABLE Syntax.
RENAME TABLE. See section 6.5.5 RENAME TABLE Syntax.
ADD, ALTER, DROP, or CHANGE
clauses in an ALTER TABLE statement.
DROP TABLE with the keywords IF EXISTS.
DROP TABLE statement.
ORDER BY and LIMIT clauses of the UPDATE and
DELETE statements.
DELAYED clause of the INSERT and REPLACE
statements.
LOW_PRIORITY clause of the INSERT, REPLACE,
DELETE, and UPDATE statements.
LOAD DATA INFILE. In many cases, this syntax is compatible with
Oracle's LOAD DATA INFILE. See section 6.4.9 LOAD DATA INFILE Syntax.
ANALYZE TABLE, CHECK TABLE, OPTIMIZE TABLE, and
REPAIR TABLE statements.
SHOW statement.
See section 4.5.7 SHOW Syntax.
SET statement. See section 5.5.6 SET Syntax.
GROUP BY part.
This gives better performance for some very specific, but quite normal
queries.
See section 6.3.7 Functions and Modifiers for Use with GROUP BY Clauses.
ASC and DESC with GROUP BY.
|| and && operators to mean
logical OR and AND, as in the C programming language. In MySQL Server,
|| and OR are synonyms, as are && and AND.
Because of this nice syntax, MySQL Server doesn't support
the standard SQL-99 || operator for string concatenation; use
CONCAT() instead. Because CONCAT() takes any number
of arguments, it's easy to convert use of the || operator to
MySQL Server.
CREATE DATABASE or DROP DATABASE.
See section 6.5.1 CREATE DATABASE Syntax.
% operator is a synonym for MOD(). That is,
N % M is equivalent to MOD(N,M). % is supported
for C programmers and for compatibility with PostgreSQL.
=, <>, <= ,<, >=,>,
<<, >>, <=>, AND, OR, or LIKE
operators may be used in column comparisons to the left of the
FROM in SELECT statements. For example:
mysql> SELECT col1=1 AND col2=2 FROM tbl_name;
LAST_INSERT_ID() function.
See section 9.1.3.31 mysql_insert_id().
REGEXP and NOT REGEXP extended regular expression
operators.
CONCAT() or CHAR() with one argument or more than two
arguments. (In MySQL Server, these functions can take any number of
arguments.)
BIT_COUNT(), CASE, ELT(),
FROM_DAYS(), FORMAT(), IF(), PASSWORD(),
ENCRYPT(), MD5(), ENCODE(), DECODE(),
PERIOD_ADD(), PERIOD_DIFF(), TO_DAYS(), or
WEEKDAY() functions.
TRIM() to trim substrings. SQL-99 supports removal
of single characters only.
GROUP BY functions STD(), BIT_OR(),
BIT_AND(), and GROUP_CONCAT().
See section 6.3.7 Functions and Modifiers for Use with GROUP BY Clauses.
REPLACE instead of DELETE + INSERT.
See section 6.4.8 REPLACE Syntax.
FLUSH, RESET and DO statements.
:=:
SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg FROM test_table; SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;
We try to make MySQL Server follow the ANSI SQL standard (SQL-92/SQL-99) and the ODBC SQL standard, but in some cases MySQL Server does things differently:
VARCHAR columns, trailing spaces are removed when the value is
stored. See section 1.8.6 Known Errors and Design Deficiencies in MySQL.
CHAR columns are silently changed to VARCHAR
columns. See section 6.5.3.1 Silent Column Specification Changes.
REVOKE to revoke privileges for
a table. See section 4.3.1 GRANT and REVOKE Syntax.
NULL AND FALSE will evaluate to NULL and not to FALSE.
This is because we don't think it's good to have to evaluate a lot of
extra conditions in this case.
For a prioritised list indicating when new extensions will be added to MySQL Server, you should consult the online MySQL TODO list at http://www.mysql.com/doc/en/TODO.html. That is the latest version of the TODO list in this manual. See section 1.9 MySQL and The Future (The TODO).
SELECTsSubqueries are supported in MySQL version 4.1. See section 1.6.1 Features Available From MySQL 4.1.
Upto version 4.0, only nested queries of the form
INSERT ... SELECT ... and REPLACE ... SELECT ...
are supported.
You can, however, use the function IN() in other contexts.
You can often rewrite the query without a subquery:
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;
Using a LEFT [OUTER] JOIN is generally much faster than an
equivalent subquery because the server can optimise it better,
a fact that is not specific to MySQL Server alone.
Prior to SQL-92, outer joins did not exist, so subqueries were the
only way to do certain things in those bygone days. But that is no
longer the case, MySQL Server and many other modern database
systems offer a whole range of outer joins types.
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 subqueries). For this situation there are three options
available:
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, ...)).
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.
SELECT INTO TABLE
MySQL Server doesn't yet support the Oracle SQL extension:
SELECT ... INTO TABLE .... Instead, MySQL Server supports the
SQL-99 syntax INSERT INTO ... SELECT ..., which is basically
the same thing. See section 6.4.3.1 INSERT ... SELECT Syntax.
INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID
FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;
Alternatively, you can use SELECT INTO OUTFILE... or
CREATE TABLE ... SELECT.
MySQL Server (version 3.23-max and all versions 4.0 and above) supports
transactions with the InnoDB and BDB
Transactional storage engines.
InnoDB provides full ACID compliance.
See section 7 MySQL Table Types.
The other non-transactional table types (such as MyISAM) in
MySQL Server follow a different paradigm for data integrity called
``Atomic Operations.'' In transactional terms, MyISAM
tables effectively always operate in AUTOCOMMIT=1 mode.
Atomic operations often offer comparable integrity with higher performance.
With MySQL Server supporting both paradigms, the user is able to decide if he needs the speed of atomic operations or if he needs to use transactional features in his applications. This choice can be made on a per-table basis.
As noted, the trade off for transactional vs. non-transactional table
types lies mostly in performance. Transactional tables have significantly
higher memory and diskspace requirements, and more CPU overhead.
That said, transactional table types such as InnoDB do of course
offer many unique features. MySQL Server's modular design allows the
concurrent use of all these different storage engines to suit different
requirements and deliver optimum performance in all situations.
But how does one use the features of MySQL Server to maintain rigorous
integrity even with the non-transactional MyISAM tables, and how
do these features compare with the transactional table types?
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.
LOCK TABLES or atomic updates, ensuring
that you never will get an automatic abort from the server, which is
a common problem with transactional database systems.
The transactional paradigm has its benefits and its drawbacks. Many users and application developers depend on the ease with which they can code around problems where an abort appears to be, or is necessary. However, even if you are new to the atomic operations paradigm, or more familiar with transactions, do consider the speed benefit that non-transactional tables can offer on the order of three to five times the speed of the fastest and most optimally tuned transactional tables.
In situations where integrity is of highest importance, MySQL Server offers
transaction-level reliability and integrity even for non-transactional tables.
If you lock tables with LOCK TABLES, all updates will stall
until any integrity checks are made. If you 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:
LOCK TABLES, and you don't need cursors when you can update
records on the fly.
ROLLBACK, you can use the following strategy:
LOCK TABLES ... to lock all the tables you want to access.
UNLOCK TABLES to release your locks.
ROLLBACKs, although not always. The only situation
this solution doesn't handle is when someone kills the threads in the
middle of an update. In this case, all locks will be released but some
of the updates may not have been executed.
WHERE clause in the UPDATE statement. If the record wasn't
updated, we give the client a message: ''Some of the data you have changed
has been changed by another user.'' Then we show the old row versus the new
row in a window, so the user can decide which version of the customer record
he should use.
This gives us something that is similar to column locking but is actually
even better because we only update some of the columns, using values that
are relative to their current values. This means that typical UPDATE
statements look something like these:
UPDATE tablename SET pay_back=pay_back+125;
UPDATE customer
SET
customer_date='current_date',
address='new address',
phone='new phone',
money_he_owes_us=money_he_owes_us-125
WHERE
customer_id=id AND address='old address' AND phone='old phone';
As you can see, this is very efficient and works even if another client
has changed the values in the pay_back or money_he_owes_us
columns.
ROLLBACK and/or LOCK
TABLES for the purpose of managing unique identifiers for some tables.
This can be handled much more efficiently by using an
AUTO_INCREMENT column and either the SQL function
LAST_INSERT_ID() or the C API function mysql_insert_id().
See section 9.1.3.31 mysql_insert_id().
You can generally code around row-level locking. Some situations really
need it, but they are very few. InnoDB tables support row-level
locking. With MyISAM, you can use a flag column in the table and do
something like the following:
UPDATE tbl_name SET row_flag=1 WHERE id=ID;MySQL returns 1 for the number of affected rows if the row was found and
row_flag wasn't already 1 in the original row.
You can think of it as though MySQL Server changed the preceding query to:
UPDATE tbl_name SET row_flag=1 WHERE id=ID AND row_flag <> 1;
Stored procedures are being implemented in our version 5.0 development tree. See section 2.3.4 Installing from the Development Source Tree.
This effort is based on SQL-99, which has a basic syntax similar (but not identical) to Oracle PL/SQL. In addition to this, we are implementing the SQL-99 framework to hook in external languages.
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 overall 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. However, stored procedures of course do increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side.
Triggers will also be implemented. A trigger is effectively a type of stored procedure, one 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 stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.
In MySQL Server 3.23.44 and up, InnoDB tables support checking of
foreign key constraints, including CASCADE, ON DELETE, and
ON UPDATE. See section 7.5.5.2 Foreign Key Constraints.
For other table types, MySQL Server only parses the FOREIGN KEY
syntax in CREATE TABLE commands, but does not use/store this info.
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.
When used as a constraint, FOREIGN KEYs don't need to be used if
the application inserts rows into MyISAM tables in the proper order.
For MyISAM tables, you can work around the lack of ON DELETE
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.
The FOREIGN KEY syntax without ON DELETE ... is often used
by ODBC applications to produce automatic WHERE clauses.
In the near future we will extend the FOREIGN KEY implementation
so that the information is stored in the table specification file
and may be retrieved by mysqldump and ODBC. At a later stage we
will implement foreign key constraints for MyISAM tables as well.
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 can make things easier.
Some advantages of foreign key enforcement:
Disadvantages:
We plan to implement views in MySQL Server in version 5.1
Historically, MySQL Server has been most used in applications and on web systems where the application writer has full control over database usage. Of course, usage has shifted over time, and so we find that an increasing number of users now regard views as an important aspect.
Views are useful for allowing users to access a set of relations as if it were a single table, and limiting their access to just that. Many DBMS don't allow updates to a view, instead you have to perform the updates on the individual tables.
Views can also be used to restrict access to rows (a subset of a particular table). One does not need views to restrict access to columns, as MySQL Server has a sophisticated privilege system. See section 4.2 General Security Issues and the MySQL Access Privilege System.
In designing our implementation of views, we aim toward (as fully as possible within the confines of SQL) compliance with ``Codd's Rule #6'' for relational database systems: all views that are theoretically updatable, should in practice also be updatable. This is a complex issue, and we are taking the time to make sure we get it right.
The implementation itself will be done in stages.
Unnamed views (derived tables, a subquery in the FROM
clause of a SELECT) are already implemented in version 4.1.
Note: If you are an enterprise level user with an urgent need for views, please contact sales@mysql.com to discuss sponsoring options. Targeted financing of this particular effort by one or more companies would allow us to allocate additional resources to it. One example of a feature sponsored in the past is replication.
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 an 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
As MySQL allows you to work with both transactional and non-transactional tables (which don't allow rollback), constraint handling is a bit different in MySQL than in other databases.
We have to handle the case when you have updated a lot of rows with a non-transactional table which can't rollback on errors.
The basic philosophy is to try to give an error for anything that we can detect on compile time but try to recover from any errors we get run time. We do this in most cases, but not yet for all. See section 1.9.4 New Features Planned For The Near Future.
The basic options MySQL has is to stop the statement in the middle or do it's best to recover from the problem and continue.
Here follows what happens with the different types of constraints.
Normally you will get an error when you try to INSERT /
UPDATE a row that causes a primary key, unique key or foreign key
violation. If you are using a transactional storage engine, like
InnoDB, MySQL will automatically roll back the transaction. If you are
using a non-transactional storage engine MySQL will stop at the wrong
row and leave the rest of the rows unprocessed.
To make life easier MySQL has added support for the IGNORE
directive to most commands that can cause a key violation (like
INSERT IGNORE ...). In this case MySQL will ignore any key
violation and continue with processing the next row. You can get
information of what MySQL did with the mysql_info() API function
and in later MySQL 4.1 version with the SHOW WARNINGS
command. See section 9.1.3.29 mysql_info(). See section 4.5.7.9 SHOW WARNINGS | ERRORS.
Note that for the moment only InnoDB tables support foreign keys.
See section 7.5.5.2 Foreign Key Constraints.
Foreign key support in MyISAM tables is scheduled for inclusion
in the MySQL 5.0 source tree.
NOT NULL and DEFAULT valuesTo be able to support easy handling of non-transactional tables all fields in MySQL have default values.
If you insert a 'wrong' value in a column like a NULL in a
NOT NULL column or a too big numerical value in a numerical
column, MySQL will instead of giving an error instead set the column to
the 'best possible value'. For numerical values this is 0, the smallest
possible values or the largest possible value. For strings this is
either the empty string or the longest possible string that can be in
the column.
This means that if you try to store NULL into a column that
doesn't take NULL values, MySQL Server will store 0 or ''
(empty string) in it instead. This last behaviour can, for single row
inserts, be changed with the -DDONT_USE_DEFAULT_FIELDS compile
option.) See section 2.3.3 Typical configure Options.
This causes INSERT statements to generate an error unless you
explicitly specify values for all columns that require a non-NULL
value.
The reason for the above rules is that we can't check these conditions before the query starts to execute. If we encounter a problem after updating a few rows, we can't just rollback as the table type may not support this. The option to stop is not that good as in this case the update would be 'half done' which is probably the worst possible scenario. In this case it's better to 'do the best you can' and then continue as if nothing happened. In MySQL 5.0 we plan to improve this by providing warnings for automatic field conversions, plus an option to let you roll back statements that only use transactional tables in case one such statement does a field assignment that is not allowed.
The above means that one should generally not use MySQL to check field content, but instead handle this in the application.
ENUM and SET
In MySQL 4.x ENUM is not a real constrain but a more efficient
way to store fields that can only contain a given set of values.
This is because of the same reasons NOT NULL is not honoured.
See section 1.8.5.2 Constraint NOT NULL and DEFAULT values.
If you insert an wrong value in an ENUM field, it will be set to
the reserved enum number 0, which will be displayed as an empty
string in string context. See section 6.2.3.3 The ENUM Type.
If you insert an wrong option in a SET field, the wrong value
will be ignored. See section 6.2.3.4 The SET Type.
The following known errors/bugs are not fixed in MySQL 3.23 because fixing them would involves changing a lot of code which could introduce other even worse bugs. The bugs are also classified as 'not fatal' or 'bearable'.
LOCK TABLE on multiple tables
and then in the same connection doing a DROP TABLE on one of
them while another thread is trying to lock the table. One can however
do a KILL on any of the involved threads to resolve this.
Fixed in 4.0.12.
SELECT MAX(key_column) FROM t1,t2,t3... where one of the tables are
empty doesn't return NULL but instead the maximum value for the
column. Fixed in 4.0.11.
DELETE FROM heap_table without a WHERE doesn't work on a locked
HEAP table.
The following problems are known and fixing them is a high priority:
ANALYZE TABLE on a BDB table may in some cases make the table
unusable until one has restarted mysqld. When this happens you will
see errors like the following in the MySQL error file:
001207 22:07:56 bdb: log_flush: LSN past current end-of-log
FROM part, but silently
ignores them. The reason for not giving an error is that many clients
that automatically generate queries add parentheses in the FROM
part even where they are not needed.
RIGHT JOINS or combining LEFT and
RIGHT join in the same query may not give a correct answer as
MySQL only generates NULL rows for the table preceding a LEFT or
before a RIGHT join. This will be fixed in 5.0 at the same time
we add support for parentheses in the FROM part.
ALTER TABLE on a BDB table on which you are
running multi-statement transactions until all those transactions complete.
(The transaction will probably be ignored.)
ANALYZE TABLE, OPTIMIZE TABLE, and REPAIR TABLE may
cause problems on tables for which you are using INSERT DELAYED.
LOCK TABLE ... and FLUSH TABLES ... doesn't
guarantee that there isn't a half-finished transaction in progress on the
table.
mysql client on the
database if you are not using the -A option or if you are using
rehash. This is especially notable when you have a big table
cache.
CREATE ... SELECT or
INSERT ... SELECT which
feeds zeros or NULLs into an auto_increment column.
DELETE if you are
deleting rows from a table which has foreign keys with ON DELETE
CASCADE properties.
REPLACE ... SELECT,
INSERT IGNORE ... SELECT if you have
duplicate key values in the inserted data.
ORDER BY
clause guarantiing a deterministic order.
Indeed, for example for INSERT ... SELECT with no ORDER
BY, the SELECT may return rows in a different order
(which will result in a row having different ranks, hence getting a
different number in the auto_increment column),
depending on the choices made by the optimisers on the master and
slave. A query will be optimised differently on the master and slave only if :
OPTIMIZE TABLE was run on the master tables and not on
the slave tables (to fix this, since MySQL 4.1.1, OPTIMIZE, ANALYZE
and REPAIR are written to the binary log).
key_buffer_size etc) are different on
the master and slave.
mysqlbinlog|mysql.
The easiest way to avoid this problem iin all cases is add an
ORDER BY clause to
such non-deterministic queries to ensure that the rows are always
stored/modified in the same order.
In future MySQL versions we will automatically add an ORDER BY
clause when needed.
The following problems are known and will be fixed in due time:
LIKE is not multi-byte character safe. Comparison is done
character by character.
RPAD function, or any other string function that ends
up adding blanks to the right, in a query that has to use temporary
table to be resolved, then all resulting strings will be RTRIM'ed. This
is an example of the query:
SELECT RPAD(t1.field1, 50, ' ') AS f2, RPAD(t2.field2, 50, '
') AS f1 FROM table1 as t1 LEFT JOIN table2 AS t2 ON
t1.record=t2.joinID ORDER BY t2.record;
Final result of this bug is that use will not be able to get blanks on
the right side of the resulting field.
The above behaviour exists in all versions of MySQL.
The reason for this is due to the fact that HEAP tables, which are used
first for temporary tables, are not capable of handling VARCHAR columns.
This behaviour will be fixed in one of the 4.1 series releases.
CHAR(255)) in table names, column names or enums.
This is scheduled to be fixed in version 5.1 when we have new table
definition format files.
SET CHARACTER SET, one can't use translated
characters in database, table, and column names.
_ or % with ESCAPE in LIKE
... ESCAPE.
DECIMAL column with a number stored in different
formats (+01.00, 1.00, 01.00), GROUP BY may regard each value
as a different value.
DELETE FROM merge_table used without a WHERE
will only clear the mapping for the table, not delete everything in the
mapped tables.
BLOB values can't ``reliably'' be used in GROUP BY or
ORDER BY or DISTINCT. Only the first max_sort_length
bytes (default 1024) are used when comparing BLOBs in these cases.
This can be changed with the -O max_sort_length option to
mysqld. A workaround for most cases is to use a substring:
SELECT DISTINCT LEFT(blob,2048) FROM tbl_name.
BIGINT or DOUBLE (both are
normally 64 bits long). It depends on the function which precision one
gets. The general rule is that bit functions are done with BIGINT
precision, IF, and ELT() with BIGINT or DOUBLE
precision and the rest with DOUBLE precision. One should try to
avoid using unsigned long long values if they resolve to be bigger than
63 bits (9223372036854775807) for anything else than bit fields.
MySQL Server 4.0 has better BIGINT handling than 3.23.
BLOB and TEXT columns, automatically
have all trailing spaces removed when retrieved. For CHAR types this
is okay, and may be regarded as a feature according to SQL-92. The bug is
that in MySQL Server, VARCHAR columns are treated the same way.
ENUM and SET columns in one table.
MIN(), MAX() and other aggregate functions, MySQL
currently compares ENUM and SET columns by their string
value rather than by the string's relative position in the set.
mysqld_safe redirects all messages from mysqld to the
mysqld log. One problem with this is that if you execute
mysqladmin refresh to close and reopen the log,
stdout and stderr are still redirected to the old log.
If you use --log extensively, you should edit mysqld_safe to
log to `'hostname'.err' instead of `'hostname'.log' so you can
easily reclaim the space for the old log by deleting the old one and
executing mysqladmin refresh.
UPDATE statement, columns are updated from left to right. If
you refer to an updated column, you will get the updated value instead of the
original value. For example:
mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1;This will update
KEY with 2 instead of with 1.
mysql> SELECT * FROM temporary_table, temporary_table AS t2;
RENAME doesn't work with TEMPORARY tables or tables used in a
MERGE table.
DISTINCT differently if you are using
'hidden' columns in a join or not. In a join, hidden columns are
counted as part of the result (even if they are not shown) while in
normal queries hidden columns don't participate in the DISTINCT
comparison. We will probably change this in the future to never compare
the hidden columns when executing DISTINCT.
An example of this is:
SELECT DISTINCT mp3id FROM band_downloads
WHERE userid = 9 ORDER BY id DESC;
and
SELECT DISTINCT band_downloads.mp3id
FROM band_downloads,band_mp3
WHERE band_downloads.userid = 9
AND band_mp3.id = band_downloads.mp3id
ORDER BY band_downloads.id DESC;
In the second case you may in MySQL Server 3.23.x get two identical rows
in the result set (because the hidden id column may differ).
Note that this happens only for queries where you don't have the
ORDER BY columns in the result, something that you are not allowed
to do in SQL-92.
rollback data, some things
behave a little differently in MySQL Server than in other SQL servers.
This is just to ensure that MySQL Server never needs to do a rollback
for an SQL command. This may be a little awkward at times as column
values must be checked in the application, but this will actually give
you a nice speed increase as it allows MySQL Server to do some
optimisations that otherwise would be very hard to do.
If you set a column to an incorrect value, MySQL Server will, instead of
doing a rollback, store the best possible value in the column:
NULL into a column that doesn't take
NULL values, MySQL Server will store 0 or '' (empty
string) in it instead. (This behaviour can, however, be changed with the
-DDONT_USE_DEFAULT_FIELDS compile option.)
DATE and
DATETIME columns (like 2000-02-31 or 2000-02-00). The idea is
that it's not the SQL server job to validate date. If MySQL can store a
date and retrieve exactly the same date, then MySQL will store the
date. If the date is totally wrong (outside the server's ability to store
it), then the special date value 0000-00-00 will be stored in the column.
ENUM column to an unsupported value, it will be set to
the error value empty string, with numeric value 0.
SET column to an unsupported value, the value will
be ignored.
PROCEDURE on a query that returns an empty set,
in some cases the PROCEDURE will not transform the columns.
MERGE doesn't check if the underlying
tables are of compatible types.
NaN, -Inf, and Inf
values in double. Using these will cause problems when trying to export
and import data. We should as an intermediate solution change NaN to
NULL (if possible) and -Inf and Inf to the
minimum respective maximum possible double value.
LIMIT on negative numbers are treated as big positive numbers.
ALTER TABLE to first add a UNIQUE index to a
table used in a MERGE table and then use ALTER TABLE to
add a normal index on the MERGE table, the key order will be
different for the tables if there was an old key that was not unique in the
table. This is because ALTER TABLE puts UNIQUE keys before
normal keys to be able to detect duplicate keys as early as possible.
The following are known bugs in earlier versions of MySQL:
DROP TABLE on a table that is
one among many tables that is locked with LOCK TABLES.
LOCK table with WRITE.
FLUSH TABLES.
UPDATE that updated a key with
a WHERE on the same key may have failed because the key was used to
search for records and the same row may have been found multiple times:
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;A workaround is to use:
mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;This will work because MySQL Server will not use an index on expressions in the
WHERE clause.
For platform-specific bugs, see the sections about compiling and porting.
This section summarises the features that we plan to implement in
MySQL Server. The lists are broken up per version, and the items
are approximately in the order they will be done.
Note: If you are an enterprise level user with an urgent need for a particular feature, please contact sales@mysql.com to discuss sponsoring options. Targeted financing by one or more companies allows us to allocate additional resources for that specific purpose. One example of a feature sponsored in the past is replication.
The features below are not yet implemented in MySQL 4.1, but are planned for implementation before MySQL 4.1 moves into its beta phase. For a list what is already done in MySQL 4.1, see section 1.6.1 Features Available From MySQL 4.1.
Development of other things has already shifted to the 5.0 tree.
The following features are planned for inclusion into MySQL 5.0. Note that because we have many developers that are working on different projects, there will also be many additional features. There is also a small chance that some of these features will be added to MySQL 4.1. For a list what is already done in MySQL 4.1, see section 1.6.1 Features Available From MySQL 4.1.
For those wishing to take a look at the bleeding edge of MySQL development, we have already made our BitKeeper repository for MySQL version 5.0 publically available. See section 2.3.4 Installing from the Development Source Tree.
RTREE index for MyISAM tables. In 4.1 RTREE indexes are
used internally for geometrical data, but not directly usable.
VARCHAR support (there is already support for this in
MyISAM).
SHOW COLUMNS FROM table_name (used by mysql client to allow
expansions of column names) should not open the table, only the
definition file. This will require less memory and be much faster.
DELETE on MyISAM tables to use the record cache.
To do this, we need to update the threads record cache when we update
the `.MYD' file.
HEAP) tables:
SET CHARACTER SET we should translate the whole query
at once and not only strings. This will enable users to use the translated
characters in database, table, and column names.
RENAME TABLE on a table used in an active
MERGE table possibly corrupting the table.
FOREIGN KEY support for all table types.
BIT type to take 1 bit (now BIT takes 1 char).
RENAME DATABASE. To make this safe for all storage engines,
it should work as follows:
RENAME command.
CONNECT BY PRIOR ... to search tree-like (hierarchical)
structures.
SUM(DISTINCT).
INSERT SQL_CONCURRENT and mysqld --concurrent-insert to do
a concurrent insert at the end of the file if the file is read-locked.
UPDATE statements. For example:
UPDATE TABLE foo SET @a=a+b,a=@a, b=@a+c.
GROUP BY, as in the following example:
SELECT id, @a:=COUNT(*), SUM(sum_col)/@a FROM table_name GROUP BY id.
IMAGE option to LOAD DATA INFILE to not update
TIMESTAMP and AUTO_INCREMENT fields.
LOAD DATA INFILE ... UPDATE syntax.
LOAD DATA INFILE ... REPLACE INTO now.
LOAD DATA INFILE understand syntax like:
LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name
TEXT_FIELDS (text_field1, text_field2, text_field3)
SET table_field1=CONCAT(text_field1, text_field2),
table_field3=23
IGNORE text_field3
This can be used to skip over extra columns in the text file,
or update columns based on expressions of the read data.
SET type columns:
ADD_TO_SET(value,set)
REMOVE_FROM_SET(value,set)
mysql in the middle of a query, you should open
another connection and kill the old running query.
Alternatively, an attempt should be made to detect this in the server.
SHOW INFO FROM tbl_name for basic table information
should be implemented.
SELECT a FROM crash_me LEFT JOIN crash_me2 USING (a); in this
case a is assumed to come from the crash_me table.
DELETE and REPLACE options to the UPDATE statement
(this will delete rows when one gets a duplicate key error while updating).
DATETIME to store fractions of seconds.
DEFAULT values to columns. Give an error
when using an INSERT that doesn't contain a column that doesn't
have a DEFAULT.
ANY(), EVERY(), and SOME() group functions. In
standard SQL these work only on boolean columns, but we can extend these to
work on any columns/expressions by applying: value == 0 -> FALSE and
value <> 0 -> TRUE.
MAX(column) is the same as the column type:
mysql> CREATE TABLE t1 (a DATE); mysql> INSERT INTO t1 VALUES (NOW()); mysql> CREATE TABLE t2 SELECT MAX(a) FROM t1; mysql> SHOW COLUMNS FROM t2;
INSERT ... SELECT to optionally use concurrent inserts.
pread()/pwrite() on Windows to enable
concurrent inserts.
SELECT MIN(column) ... GROUP BY.
long_query_time with a granularity
in microseconds.
myisampack code into the server, enabling a PACK or
COMPRESS command on the server.
INSERT/DELETE/UPDATE so that we
can gracefully recover if the index file gets full.
ALTER TABLE on a table that is symlinked to another
disk, create temporary tables on this disk.
DATE/DATETIME type that handles time zone information
properly so that dealing with dates in different time zones is easier.
MyISAM)
without threads.
LIMIT, like in LIMIT @a,@b.
mysql to a web browser.
LOCK DATABASES (with various options).
SHOW STATUS. Records reads and
updates. Selects on 1 table and selects with joins. Mean number of
tables in select. Number of ORDER BY and GROUP BY queries.
mysqladmin copy database new-database; requires COPY
command to be added to mysqld.
SHOW HOSTS for printing information about the hostname cache.
NULL for calculated columns.
Item_copy_string on numerical values to avoid
number->string->number conversion in case of:
SELECT COUNT(*)*(id+0) FROM table_name GROUP BY id
ALTER TABLE doesn't abort clients
that execute INSERT DELAYED.
UPDATE clause,
they contain the old values from before the update started.
get_changed_tables(timeout,table1,table2,...).
SET TIMESTAMP=#;.
MINUS, INTERSECT, and FULL OUTER JOIN.
(Currently UNION [in 4.0] and LEFT|RIGHT OUTER JOIN are supported.)
SQL_OPTION MAX_SELECT_TIME=# to put a time limit on a query.
LIMIT to allow retrieval of data from the end of a result set.
mysqld_safe: according to FSSTND (which
Debian tries to follow) PID files should go into `/var/run/<progname>.pid'
and log files into `/var/log'. It would be nice if you could put the
"DATADIR" in the first declaration of "pidfile" and "log", so the
placement of these files can be changed with a single statement.
zlib() for gzip-ed files to LOAD DATA INFILE.
BLOB columns (partly solved now).
AUTO_INCREMENT value when one sets a column to 0.
Use NULL instead.
JOIN with parentheses.
GET_LOCK. When doing this,
one must also handle the possible deadlocks this change will introduce.
Time is given according to amount of work, not real time.
Our users have successfully run their own benchmarks against a number
of Open Source and traditional database servers.
We are aware of tests against Oracle 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 benchmarks@mysql.com.
For comparative lists of all supported functions and types as well
as measured operational limits of many different database systems,
see the crash-me web page at
http://www.mysql.com/information/crash-me.php.
mSQLmSQL should be quicker at:
INSERT operations into very simple tables with few columns and keys.
CREATE TABLE and DROP TABLE.
SELECT on something that isn't indexed. (A table scan is very
easy.)
mSQL (and
most other SQL implementations) on the following:
SELECT operations.
VARCHAR columns.
SELECT with many expressions.
SELECT on large tables.
mSQL, once one
connection is established, all others must wait until the first has
finished, regardless of whether the connection is running a query
that is short or long. When the first connection terminates, the
next can be served, while all the others wait again, etc.
mSQL can become pathologically slow if you change the order of
tables in a SELECT. In the benchmark suite, a time more than
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.
TEXT or BLOB columns.
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;
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).
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.
mSQL stability, so we cannot say
anything about that.
mSQL, and is also less expensive
than mSQL. Whichever product you choose to use, remember to
at least consider paying for a license or e-mail support.
mSQL with
some added features.
GPL and commercial).
mSQL has a JDBC driver, but we have too little
experience with it to compare.
GROUP BY, and so on are still not implemented in mSQL, it
has a lot of catching up to do. To get some perspective on this, you
can view the mSQL `HISTORY' file for the last year and
compare it with the News section of the MySQL Reference Manual
(see section D MySQL Change History). It should be pretty obvious which one has developed
most rapidly.
mSQL and MySQL 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.
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:
msql2mysql on the source. This requires
the replace program, which is distributed with MySQL Server.
Differences between the mSQL C API and the MySQL C API are:
MYSQL structure as a connection type (mSQL
uses an int).
mysql_connect() takes a pointer to a MYSQL structure as a
parameter. It is easy to define one globally or to use malloc()
to get one. mysql_connect() also takes two parameters for
specifying the user and password. You may set these to
NULL, NULL for default use.
mysql_error() takes the MYSQL structure as a parameter.
Just add the parameter to your old msql_error() code if you are
porting old code.
mSQL returns only a text error message.
mSQL and MySQL Client/Server Communications Protocols DifferThere are enough differences that it is impossible (or at least not easy) to support both.
The most significant ways in which the MySQL protocol differs
from the mSQL protocol are listed here:
mSQL 2.0 SQL Syntax Differs from MySQLColumn types
MySQL Server
CREATE TABLE Syntax):
ENUM type for one of a set of strings.
SET type for many of a set of strings.
BIGINT type for 64-bit integers.
UNSIGNED option for integer and floating-point columns.
ZEROFILL option for integer columns.
AUTO_INCREMENT option for integer columns that are a
PRIMARY KEY.
See section 9.1.3.31 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 SQL-99 format rather than mSQL's own format.
|
TIME | TIME
|
MONEY | DECIMAL(12,2). A fixed-point value with two decimals.
|
Index Creation
MySQL Server
CREATE TABLE
statement.
mSQL
CREATE INDEX statements.
To Insert a Unique Identifier into a Table
MySQL Server
AUTO_INCREMENT as a column type
specifier.
See section 9.1.3.31 mysql_insert_id().
mSQL
SEQUENCE on a table and select the _seq column.
To Obtain a Unique Identifier for a Row
MySQL Server
PRIMARY KEY or UNIQUE key to the table and use this.
New in Version 3.23.11: If the PRIMARY or UNIQUE key consists of only one
column and this is of type integer, one can also refer to it as
_rowid.
mSQL
_rowid column. Observe that _rowid may change over time
depending on many factors.
To Get the Time a Column Was Last Modified
MySQL Server
TIMESTAMP column to the table. This column is automatically set
to the current date and time for INSERT or UPDATE statements if
you don't give the column a value or if you give it a NULL value.
mSQL
_timestamp column.
NULL Value Comparisons
MySQL Server
NULL is always UNKNOWN.
mSQL
mSQL, NULL = NULL is TRUE. You
must change =NULL to IS NULL and <>NULL to
IS NOT NULL when porting old code from mSQL to MySQL Server.
String Comparisons
MySQL Server
BINARY attribute, which causes comparisons to be done according to the
ASCII order used on the MySQL server host.
mSQL
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
CLIKE.
Handling of Trailing Spaces
MySQL Server
CHAR and VARCHAR
columns. Use a TEXT column if this behaviour is not desired.
mSQL
WHERE Clauses
MySQL Server
AND is evaluated
before OR). To get mSQL behaviour in MySQL Server, use
parentheses (as shown in an example later in this section).
mSQL
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
mSQL
PostgreSQLWhen reading the following, please note that both products are continually evolving. MySQL AB's and PostgreSQL's developers are both working on making our respective databases as good as possible. Both products are thus 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 SQL standard compliance. 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.
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 is 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.
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:
MySQL Server is generally much faster than PostgreSQL. MySQL
4.0.1 also has a query cache that can boost up the query speed for
mostly-read-only sites many times.
Cygwin emulation. We have
heard that PostgreSQL is not yet that stable on Windows but we haven't
been able to verify this ourselves.
VACUUM
once in a while to reclaim space from UPDATE and DELETE
commands and to perform statistics analyses that are critical to get
good performance with PostgreSQL. VACUUM is also needed after
adding a lot of new rows to a table. On a busy system with lots of changes,
VACUUM must be run very frequently, in the worst cases even
many times a day. During the VACUUM run, which may take hours
if the database is big, the database is, from a production standpoint,
practically dead. Please note: in PostgreSQL version 7.2, basic vacuuming
no longer locks tables, thus allowing normal user access during the vacuum.
A new VACUUM FULL command does old-style vacuum by locking the table
and shrinking the on-disk copy of the table.
crash-me
(http://www.mysql.com/information/crash-me.php), as well
as a benchmark suite. The test system is actively updated with code to
test each new feature and almost all reproducible bugs that have come to
our attention. We test MySQL Server with these on a lot of platforms before
every release. These tests are more sophisticated than anything we have
seen from PostgreSQL, and they ensure that the MySQL Server is kept to a high
standard.
PostgreSQL.
ALTER TABLE.
HEAP
tables or disk based MyISAM. See section 7 MySQL Table Types.
InnoDB, and BerkeleyDB. Because every
transaction engine performs differently under different conditions, this
gives the application writer more options to find an optimal solution for
his or her setup, if need be per individual table. See section 7 MySQL Table Types.
MERGE tables gives you a unique way to instantly make a view over
a set of identical tables and use these as one. This is perfect for
systems where you have log files that you order, for example, by month.
See section 7.2 MERGE Tables.
myisampack, The MySQL Compressed Read-only Table Generator.
INSERT,
SELECT, and UPDATE/DELETE grants per user on a database or
a table, MySQL Server allows you to define a full set of different
privileges on the database, table, and column level. MySQL Server also
allows you to specify the privilege on host and user combinations.
See section 4.3.1 GRANT and REVOKE Syntax.
InnoDB) are implemented as files
(one table per file), which makes it really easy to back up, move, delete,
and even symlink databases and tables, even when the server is down.
MyISAM tables (the most common
MySQL table type). A repair tool is only needed when a physical corruption
of a datafile happens, usually from a hardware failure. It allows a
majority of the data to be recovered.
Drawbacks with MySQL Server compared to PostgreSQL:
MyISAM tables, is
in many cases faster than page locks, row locks, or versioning. The
drawback, however, is that if one doesn't take into account how table
locks work, a single long-running query can block a table for updates
for a long time. This can usually be avoided when designing the
application. If not, one can always switch the trouble table to use one
of the transactional table types. See section 5.3.2 Table Locking Issues.
UPDATE and in MySQL Server 4.1 with subqueries.
In MySQL Server 4.0 one can use multi-table deletes to delete from many
tables at the same time. See section 6.4.6 DELETE Syntax.
PostgreSQL currently offers the following advantages over MySQL 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 |
| Subqueries | 4.1 |
| Foreign keys | 5.1 (3.23 with InnoDB) |
| Views | 5.1 |
| Stored procedures | 5.0 |
| Triggers | 5.1 |
| Unions | 4.0 |
| Full outer join | 5.1 |
| Constraints | 5.1 |
| Cursors | 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:
VACUUM makes PostgreSQL hard to use in a 24/7 environment.
INSERT, DELETE, and UPDATE.
For a complete list of drawbacks, you should also examine the first table in this section.
The only Open Source benchmark that we know of that can be used to
benchmark MySQL 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 daemon) 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 are both 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.
Open Source company like us to verify the benchmarks,
or even check how the benchmarks were really done. The tool is not even
a true benchmark tool, but an application/setup testing tool. To refer
to this as a ``standard'' benchmark tool is to stretch the truth a long way.
VACUUM before the test) and tuned the startup for the tests,
something they hadn't done for any of the other databases involved. They
say ``This process optimises indexes and frees up disk space a bit. The
optimised indexes boost performance by some margin.'' Our benchmarks
clearly indicate that the difference in running a lot of selects on a
database with and without VACUUM can easily differ by a factor
of 10.
SELECTs and JOINs (especially
after a VACUUM), but doesn't perform as well on INSERTs or
UPDATEs. The benchmarks seem to indicate that only SELECTs
were done (or very few updates). This could easily explain the good results
for PostgreSQL in this test. The bad results for MySQL will be obvious a
bit down in this document.
Tim Perdue, a long-time PostgreSQL fan and a reluctant MySQL user, published a comparison on PHPbuilder (http://www.phpbuilder.com/columns/tim20001112.php3).
When we became aware of the comparison, we phoned Tim Perdue about this because there were a lot of strange things in his results. For example, he claimed that MySQL Server had a problem with five users in his tests, when we know that there are users with similar machines running 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 had some problems with many threads, such as kernels before 2.4, which had a problem with many threads on multi-CPU machines. This manual describes the fix for 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 no longer very relevant. MySQL Server now has a couple of different storage engines 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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