When you create a new table, you can specify which storage engine
to use by adding an
ENGINE table option to the
CREATE TABLE statement:
-- ENGINE=INNODB not needed as of 5.5.5 unless you have set a -- different default storage engine. CREATE TABLE t1 (i INT) ENGINE = INNODB; -- Simple table definitions can be switched from one to another. CREATE TABLE t2 (i INT) ENGINE = CSV; CREATE TABLE t3 (i INT) ENGINE = MEMORY;
If you omit the
ENGINE option, the default
storage engine is used. The default engine is
InnoDB as of MySQL 5.5.5
MyISAM before 5.5.5). You can
specify the default engine by using the
startup option, or by setting the
default-storage-engine option in
my.cnf configuration file.
At runtime, you can set the default storage engine to be used
during the current session by setting the
When MySQL is installed on Windows using the MySQL Configuration
storage engine can be selected as the default. See
Section 188.8.131.52, “The Database Usage Dialog”.
To convert a table from one storage engine to another, use an
ALTER TABLE statement that
indicates the new engine:
ALTER TABLE t ENGINE = MYISAM;
If you try to use a storage engine that is not compiled in or that is compiled in but deactivated, MySQL instead creates a table using the default storage engine. This behavior is convenient when you want to copy tables between MySQL servers that support different storage engines. (For example, in a replication setup, perhaps your master server supports transactional storage engines for increased safety, but the slave servers use only nontransactional storage engines for greater speed.)
This automatic substitution of the default storage engine for
unavailable engines can be confusing for new MySQL users. A
warning is generated whenever a storage engine is automatically
changed. To prevent this from happening if the desired engine is
unavailable, enable the
NO_ENGINE_SUBSTITUTION SQL mode.
In this case, an error occurs instead of a warning and the table
is not created or altered if the desired engine is unavailable.
See Section 5.1.10, “Server SQL Modes”.
For new tables, MySQL always creates an
file to hold the table and column definitions. The table's index
and data may be stored in one or more other files, depending on
the storage engine. The server creates the
.frm file above the storage engine level.
Individual storage engines create any additional files required
for the tables that they manage. If a table name contains special
characters, the names for the table files contain encoded versions
of those characters as described in
Section 9.2.4, “Mapping of Identifiers to File Names”.
A database may contain tables of different types. That is, tables need not all be created with the same storage engine.