MySQL Server includes some extensions that you probably will not find in
other SQL databases. Be warned that if you use them, your code will not be
portable to other SQL servers. In some cases, you can write code that
includes MySQL extensions, but is still portable, by using comments
of the form /*! ... */. In this case, MySQL Server will parse and
execute the code within the comment as it would any other MySQL
statement, but other SQL servers will ignore the extensions. For example:
SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ...
If you add a version number after the '!' character, the syntax within
the comment will be
executed only if the MySQL version is equal to or newer than the specified
version number:
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 descriptions list MySQL extensions, organized by category.
Organization of data on disk
MySQL Server maps each database to a directory under the MySQL
data directory, and tables within a database to filenames in the database
directory.
This has a few implications:
Database names and table names are case sensitive in MySQL Server on
operating systems that have case sensitive filenames (like most Unix
systems). See Name case sensitivity.
Database, table, index, column, or alias names may begin with a digit
(but may not consist solely of digits).
You can use standard system commands to back up, rename, move, delete, and copy
tables that are managed by the MyISAM or ISAM storage engines.
For example, to rename a MyISQM table, rename the .MYD,
.MYI, and .frm files to which the table corresponds.
General language syntax
Strings may be enclosed by either " or ', not just by '.
Use of \ as an escape character in strings.
In SQL statements, you can access tables from different databases
with the db_name.tbl_name syntax. Some SQL servers provide
the same functionality but call this User space.
MySQL Server doesn't support tablespaces such as used in statements like this:
CREATE TABLE ralph.my_table...IN my_tablespace.
SQL statement syntax
The ANALYZE TABLE, CHECK TABLE, OPTIMIZE TABLE, and
REPAIR TABLE statements.
The CREATE DATABASE and DROP DATABASE statements.
See CREATE DATABASE.
The DO statement.
EXPLAIN SELECT to get a description of how tables are joined.
Use of REPLACE instead of DELETE + INSERT.
See REPLACE.
Use of CHANGE col_name, DROP col_name, or DROP INDEX, IGNORE or RENAME in an ALTER TABLE
statement.
Use of multiple ADD, ALTER, DROP, or CHANGE
clauses in an ALTER TABLE statement.
See ALTER TABLE.
Use of index names, indexes on a prefix of a field, and use of
INDEX or KEY in a CREATE TABLE
statement. See CREATE TABLE.
Use of TEMPORARY or IF NOT EXISTS with CREATE TABLE.
Use of IF EXISTS with DROP TABLE.
You can drop multiple tables with a single DROP TABLE statement.
The ORDER BY and LIMIT clauses of the UPDATE and
DELETE statements.
INSERT INTO ... SET col_name = ... syntax.
The DELAYED clause of the INSERT and REPLACE
statements.
The LOW_PRIORITY clause of the INSERT, REPLACE,
DELETE, and UPDATE statements.
Use of INTO OUTFILE and STRAIGHT_JOIN in a SELECT
statement. See SELECT.
The SQL_SMALL_RESULT option in a SELECT statement.
You don't need to name all selected columns in the GROUP BY part.
This gives better performance for some very specific, but quite normal
queries.
See Group by functions and modifiers.
You can specify ASC and DESC with GROUP BY.
The ability to set variables in a statement with the := assignment
operator:
mysql> SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg
-> FROM test_table;
mysql> SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;
Column types
The column types MEDIUMINT, SET, ENUM, and the
different BLOB and TEXT types.
The column attributes AUTO_INCREMENT, BINARY, NULL,
UNSIGNED, and ZEROFILL.
Functions and operators
To make it easier for users who come from other SQL environments,
MySQL Server supports aliases for many functions. For example, all
string functions support both standard SQL syntax and ODBC syntax.
MySQL Server understands the || 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.
Use of COUNT(DISTINCT list) where list has more than one element.
All string comparisons are case-insensitive by default, with sort
ordering determined by the current character set (ISO-8859-1 Latin1 by
default). If you don't like this, you should declare your columns with
the BINARY attribute or use the BINARY cast, which causes
comparisons to be done according to the ASCII order used on the
MySQL server host.
The % 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.
The =, <>, <= ,<, >=,>,
<<, >>, <=>, AND, OR, or LIKE
operators may be used in column comparisons to the left of the
FROM in SELECT statements. For example:
For a prioritized list indicating when new extensions will be added to
MySQL Server, you should consult the online MySQL TODO list at
http://www.mysql.com/doc/en/TODO.html.
That is the latest version of the TODO list in this manual. See TODO.