To subscribe to or unsubscribe from any of the mailing lists described in this section, visit http://lists.mysql.com/. For most of them, you can select the regular version of the list where you get individual messages, or a digest version where you get one large message per day.

Please do not send messages about subscribing or unsubscribing to any of the mailing lists, because such messages are distributed automatically to thousands of other users.

Your local site may have many subscribers to a MySQL mailing list. If so, the site may have a local mailing list, so that messages sent from lists.mysql.com to your site are propagated to the local list. In such cases, please contact your system administrator to be added to or dropped from the local MySQL list.

If you wish to have traffic for a mailing list go to a separate mailbox in your mail program, set up a filter based on the message headers. You can use either the List-ID: or Delivered-To: headers to identify list messages.

The MySQL mailing lists are as follows:

If you're unable to get an answer to your questions from a MySQL mailing list or forum, one option is to purchase support from MySQL AB. This puts you in direct contact with MySQL developers.

The following table shows some MySQL mailing lists in languages other than English. These lists are not operated by MySQL AB.

Before posting a bug report or question, please do the following:

If you can't find an answer in the manual or the archives, check with your local MySQL expert. If you still can't find an answer to your question, please follow the guidelines on sending mail to a MySQL mailing list, outlined in the next section, before contacting us.

The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log in to the system, you can 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 helps 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 example, 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_file on the included test case or by running the shell or Perl script that is included in the bug report.

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

If you have found a sensitive security bug in MySQL, you can send email to <security@mysql.com>.

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

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

Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is this: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.

The most common errors made in bug reports are (a) not including the version number of the MySQL distribution used, and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and version number). This is highly relevant information, and in 99 cases out of 100, the bug report is useless without it. Very often we get questions like, “Why doesn't this work for me?” Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has been fixed in newer MySQL versions. Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.

If you compiled MySQL from source, remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is MySQL-related. Most compilers are under development all the time and become better version by version. To determine whether your problem depends on your compiler, we need to know what compiler you use. Note that every compiling problem should be regarded as a bug and reported accordingly.

It is most helpful when a good description of the problem is included in the bug report. That is, give a good example of everything you did that led to the problem and describe, in exact detail, the problem itself. The best reports are those that include a full example showing how to reproduce the bug or problem. See Section 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 lettercase should be observed.) You should never try to reproduce from memory what the error message was; instead, copy and paste the entire message into your report.

If you have a problem with Connector/ODBC (MyODBC), please try to generate a trace file and send it with your report. See Section 24.1.1.9, “How to Report MyODBC Problems or Bugs”.

Please remember that many of the people who read your report do so using an 80-column display. When generating reports or examples using the mysql command-line tool, you should therefore use the --vertical option (or the \G statement terminator) for output that would exceed the available width for such a display (for example, with the EXPLAIN SELECT statement; see the example later in this section).

Please include the following information in your report:

If you are a support customer, please cross-post the bug report to <mysql-support@mysql.com> for higher-priority treatment, as well as to the appropriate mailing list to see whether someone else has experienced (and perhaps solved) the problem.

For information on reporting bugs in MyODBC, see Section 24.1.1.9, “How to Report MyODBC Problems or Bugs”.

For solutions to some common problems, see Appendix A, Problems and Common Errors.

When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarize the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem.

If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer.

Try to summarize the essential part of the question in your reply; don't feel obliged to quote the entire original message.

Please don't post mail messages from your browser with HTML mode turned on. Many users don't read mail with a browser.

MySQL 4.1 supports subqueries and derived tables. A “subquery” is a SELECT statement nested within another statement. A “derived table” (an unnamed view) is a subquery in the FROM clause of another statement. See Section 13.2.8, “Subquery Syntax”.

For MySQL versions older than 4.1, most subqueries can be rewritten using joins or other methods. See Section 13.2.8.11, “Rewriting Subqueries as Joins for Earlier MySQL Versions” for examples that show how to do this.

MySQL Server doesn't support the Sybase SQL extension: SELECT ... INTO TABLE .... Instead, MySQL Server supports the standard SQL syntax INSERT INTO ... SELECT ..., which is basically the same thing. See Section 13.2.4.1, “INSERT ... SELECT Syntax”.

INSERT INTO tbl_temp2 (fld_id)
    SELECT tbl_temp1.fld_order_id
    FROM tbl_temp1 WHERE tbl_temp1.fld_order_id > 100;

Alternatively, you can use SELECT INTO OUTFILE ... or CREATE TABLE ... SELECT.

From version 5.0, MySQL supports SELECT ... INTO with user variables. The same syntax may also be used inside stored procedures using cursors and local variables. See Section 18.2.9.3, “SELECT ... INTO Statement”.

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 Chapter 14, Storage Engines and Table Types.

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

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

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

But how do you 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?

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 stall until integrity checks are made. If you obtain a READ LOCAL lock (as opposed to a write lock) for a table that allows concurrent inserts at the end of the table, reads are allowed, as are inserts by other clients. The newly inserted records are not be seen by the client that has the read lock until it releases the lock. With INSERT DELAYED, you can queue inserts into a local queue, until the locks are released, without having the client wait for the insert to complete. See Section 13.2.4.2, “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 can never be an automatic rollback (which can happen with transactional tables if you are not very careful). MySQL Server also guarantees that there are no dirty reads.

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

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

Basic triggers functionality is implemented in MySQL beginning with version 5.0.2, with further development planned in MySQL 5.1. See Chapter 19, Triggers.

In MySQL Server 3.23.44 and up, the InnoDB storage engine supports checking of foreign key constraints, including CASCADE, ON DELETE, and ON UPDATE. See Section 15.6.4, “FOREIGN KEY Constraints”.

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

Foreign key enforcement offers several benefits to database developers:

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

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

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

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

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

SELECT * FROM t1, t2 WHERE t1.id = t2.id;

See Section 13.2.7.1, “JOIN Syntax”. See Section 3.6.6, “Using Foreign Keys”.

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

Views (including updatable views) are implemented in the 5.0 version of MySQL Server. Views are available in binary releases from 5.0.1 and up. See Chapter 20, Views.

Views are useful for allowing users to access a set of relations (tables) as if it were a single table, and limiting their access to just that. Views can also be used to restrict access to rows (a subset of a particular table). For access control to columns, you can also use the sophisticated privilege system in MySQL Server. See Section 5.7, “The MySQL Access Privilege System”.

In designing an implementation of views, our ambitious goal, as much as is possible within the confines of SQL, has been full compliance with “Codd's Rule #6” for relational database systems: “All views that are theoretically updatable, should in practice also be updatable.”

Some other SQL databases use ‘--’ to start comments. MySQL Server uses ‘#’ as the start comment character. You can also use the C comment style /* this is a comment */ with MySQL Server. See Section 9.5, “Comment Syntax”.

MySQL Server 3.23.3 and above support the ‘--’ comment style, provided the comment is followed by a space (or by a control character such as a newline). The requirement for a space is to prevent problems with automatically generated SQL queries that have used something like the following code, where we automatically insert the value of the payment for !payment!:

UPDATE account SET credit=credit-!payment!

Think about what happens if the value of payment is a negative value such as -1:

UPDATE account SET credit=credit--1

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

UPDATE account SET credit=credit

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

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

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

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

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

shell> replace " --" " #" < text-file-with-funny-comments.sql \
         | mysql db_name

instead of the usual:

shell> mysql db_name < 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

Normally, an error occurs when you try to INSERT or UPDATE a row that causes a primary key, unique key, or foreign key violation. If you are using a transactional storage engine such as InnoDB, MySQL automatically rolls back the statement. If you are using a non-transactional storage engine, MySQL stops processing the statement at the row for which the error occurred and leaves any remaining rows unprocessed.

If you wish to ignore such key violations, MySQL supports an IGNORE keyword for INSERT and UPDATE. In this case, MySQL ignores any key violations and continues processing with the next row. See Section 13.2.4, “INSERT Syntax”. See Section 13.2.10, “UPDATE Syntax”.

You can get information about the number of rows actually inserted or updated with the mysql_info() C API function. See Section 23.2.3.34, “mysql_info()”. In MySQL 4.1 and up, you also can use the SHOW WARNINGS statement. See Section 13.5.4.22, “SHOW WARNINGS Syntax”.

For the moment, only InnoDB tables support foreign keys. See Section 15.6.4, “FOREIGN KEY Constraints”. Foreign key support in MyISAM tables is scheduled for implementation in MySQL 5.1.

Before MySQL 5.0.2, MySQL is forgiving of illegal or improper data values and coerces them to legal values for data entry. In MySQL 5.0.2 and up, that remains the default behavior, but you can select more traditional treatment of bad values such that the server rejects them and aborts the statement in which they occur. This section describes the default (forgiving) behavior of MySQL, as well as the newer strict SQL mode and how it differs.

The following holds true when you are not using strict mode. If you insert an “incorrect” value into a column, such as a NULL into a NOT NULL column or a too-large numeric value into a numeric column, MySQL sets the column to the “best possible value” instead of producing an error:

The reason for the preceding rules is that we can't check these conditions until the statement has begun executing. We can't just roll back if we encounter a problem after updating a few rows, because the storage engine may not support rollback. The option of terminating the statement is not that good; in this case, the update would be “half done,” which is probably the worst possible scenario. In this case, it's better to “do the best you can” and then continue as if nothing happened.

In MySQL 5.0.2 and up, you can select stricter treatment of input values by using the STRICT_TRANS_TABLES or STRICT_ALL_TABLES SQL modes. See Section 5.3.2, “The Server SQL Mode”.

STRICT_TRANS_TABLES works like this:

For stricter checking, enable STRICT_ALL_TABLES. This is the same as STRICT_TRANS_TABLES except that for non-transactional storage engines, errors abort the statement even for bad data in rows following the first row. This means that if an error occurs partway through a multiple-row insert or update for a non-transactional table, a partial update results. Earlier rows are inserted or updated, but those from the point of the error on are not. To avoid this for non-transactional tables, either use single-row statements or else use STRICT_TRANS_TABLES if conversion warnings rather than errors are acceptable. To avoid problems in the first place, do not use MySQL to check column content. It is safest (and often faster) to let the application ensure that it passes only legal values to the database.

With either of the strict mode options, you can cause errors to be treated as warnings by using INSERT IGNORE or UPDATE IGNORE rather than INSERT or UPDATE without IGNORE.

ENUM and SET columns provide an efficient way to define columns that can contain only a given set of values. However, before MySQL 5.0.2, ENUM and SET are not real constraints. This is for the same reasons that NOT NULL is not honored. See Section 1.8.6.2, “Constraints on Invalid Data”.

ENUM columns always have a default value. If you don't specify a default value, then it is NULL for columns that can have NULL, otherwise the first enumeration value is used as the default value.

If you insert an incorrect value into an ENUM column or if you force a value into an ENUM column with IGNORE, it is set to the reserved enumeration value of 0, which is displayed as an empty string in string context. See Section 11.4.4, “The ENUM Type”.

If you insert an incorrect value into a SET column, the incorrect value is ignored. For example, if the column can contain the values 'a', 'b', and 'c', an attempt to assign 'a,x,b,y' results in a value of 'a,b'. See Section 11.4.5, “The SET Type”.

As of MySQL 5.0.2, you can configure the server to use strict SQL mode. See Section 5.3.2, “The Server SQL Mode”. When strict mode is enabled, the definition of a ENUM or SET column does act as a constraint on values entered into the column. An error occurs for values that do not satisfy these conditions:

Errors for invalid values can be suppressed in strict mode if you use INSERT IGNORE or UPDATE IGNORE. In this case, a warning is generated rather than an error. For ENUM, the value is inserted as the error member (0). For SET, the value is inserted as given except that any invalid substrings are deleted. For example, 'a,x,b,y' results in a value of 'a,b', as described earlier.