tbl_name] ... [ QUICK | EXTENDED ]
CHECKSUM TABLE reports a checksum for the contents of a
table. You can use this statement to verify that the contents are the same before and after a backup, rollback,
or other operation that is intended to put the data back to a known state. This statement requires the
SELECT privilege for the
By default, the entire table is read row by row and the checksum is calculated. For large tables, this could
take a long time, thus you would only perform this operation occasionally. This row-by-row calculation is what
you get with the
EXTENDED clause, with
InnoDB and all
other storage engines other than
MyISAM, and with
MyISAM tables not created with the
MyISAM tables created with the
CHECKSUM TABLE or
CHECKSUM TABLE ... QUICK returns the
"live" table checksum that can be returned very fast. If
the table does not meet all these conditions, the
QUICK method returns
NULL. See Section 13.1.14, "
CREATE TABLE Syntax" for the syntax of the
For a nonexistent table,
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.
If the checksums for two tables are different, then it is almost certain that the tables are
different in some way. However, because the hashing function used by
CHECKSUM TABLE is not guaranteed to be collision-free, there is a slight
chance that two tables which are not identical can produce the same checksum.