18.104.22.168 CHECKSUM TABLE Statement
CHECKSUM TABLE tbl_name [, 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 table.
This statement is not supported for views. If you run
CHECKSUM TABLE against a view, the
Checksum value is always
NULL, and a warning is returned.
For a nonexistent table,
CHECKSUM TABLE returns
NULL and generates a warning.
During the checksum operation, the table is locked with a read lock for
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
QUICK method is not supported with
InnoDB tables. See Section 13.1.18, “CREATE TABLE Statement” for the syntax of the
The checksum value depends on the table row format. If the row format changes, the checksum also changes. For example, the storage format for temporal types such as
TIMESTAMP changed in MySQL 5.6 prior to MySQL 5.6.5, so if a 5.5 table is upgraded to MySQL 5.6, 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.