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12.4.2.4 OPTIMIZE TABLE Syntax »
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12.4.2.3. CHECKSUM TABLE Syntax

CHECKSUM TABLE tbl_name [, tbl_name] ... [ QUICK | EXTENDED ]

CHECKSUM TABLE reports a table checksum. This statement requires the SELECT privilege for the table.

With QUICK, the live table checksum is reported if it is available, or NULL otherwise. This is very fast. A live checksum is enabled by specifying the CHECKSUM=1 table option when you create the table; currently, this is supported only for MyISAM tables. See Section 12.1.14, “CREATE TABLE Syntax”.

With EXTENDED, the entire table is read row by row and the checksum is calculated. This can be very slow for large tables.

If neither QUICK nor EXTENDED is specified, MySQL returns a live checksum if the table storage engine supports it and scans the table otherwise.

For a nonexistent table, CHECKSUM TABLE returns NULL and generates a warning.

The checksum value depends on the table row format. If the row format changes, the checksum also changes. For example, the storage format for VARCHAR changed between MySQL 4.1 and 5.0, so if a 4.1 table is upgraded to MySQL 5.0, the checksum value may change.

Important

If the checksums for two tables are different, then the tables are different in some way. However, the fact that two tables produce the same checksum does not mean that the tables are identical.