CHECK TABLE tbl_name [, tbl_name] ... [option] ...

option = {
  | FAST

CHECK TABLE checks a table or tables for errors. CHECK TABLE works for InnoDB, MyISAM, and ARCHIVE tables. Starting with MySQL 5.1.9, CHECK TABLE is also valid for CSV tables, see Section 14.13, “The CSV Storage Engine”. For MyISAM tables, the key statistics are updated as well.

CHECK TABLE can also check views for problems, such as tables that are referenced in the view definition that no longer exist.

Beginning with MySQL 5.1.27, CHECK TABLE is also supported for partitioned tables. Also beginning with MySQL 5.1.27, you can use ALTER TABLE ... CHECK PARTITION to check one or more partitions; for more information, see Section 13.1.7, “ALTER TABLE Syntax”, and Section 18.3.3, “Maintenance of Partitions”.


CHECK TABLE returns a result set with the following columns.

TableThe table name
OpAlways check
Msg_typestatus, error, info, note, or warning
Msg_textAn informational message

The statement might produce many rows of information for each checked table. The last row has a Msg_type value of status and the Msg_text normally should be OK. If you don't get OK, or Table is already up to date for a MyISAM table, you should normally run a repair of the table. See Section 7.6, “MyISAM Table Maintenance and Crash Recovery”. Table is already up to date means that the storage engine for the table indicated that there was no need to check the table.

Checking Version Compatibility

The FOR UPGRADE option checks whether the named tables are compatible with the current version of MySQL. This option was added in MySQL 5.1.7. With FOR UPGRADE, the server checks each table to determine whether there have been any incompatible changes in any of the table's data types or indexes since the table was created. If not, the check succeeds. Otherwise, if there is a possible incompatibility, the server runs a full check on the table (which might take some time). If the full check succeeds, the server marks the table's .frm file with the current MySQL version number. Marking the .frm file ensures that further checks for the table with the same version of the server will be fast.

Incompatibilities might occur because the storage format for a data type has changed or because its sort order has changed. Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases.

FOR UPGRADE discovers these incompatibilities:

Checking Data Consistency

The following table shows the other check options that can be given. These options are passed to the storage engine, which may use them or not.

QUICKDo not scan the rows to check for incorrect links. Applies to InnoDB and MyISAM tables and views.
FASTCheck only tables that have not been closed properly. Applies only to MyISAM tables and views; ignored for InnoDB.
CHANGEDCheck only tables that have been changed since the last check or that have not been closed properly. Applies only to MyISAM tables and views; ignored for InnoDB.
MEDIUMScan rows to verify that deleted links are valid. This also calculates a key checksum for the rows and verifies this with a calculated checksum for the keys. Applies only to MyISAM tables and views; ignored for InnoDB.
EXTENDEDDo a full key lookup for all keys for each row. This ensures that the table is 100% consistent, but takes a long time. Applies only to MyISAM tables and views; ignored for InnoDB.

If none of the options QUICK, MEDIUM, or EXTENDED are specified, the default check type for dynamic-format MyISAM tables is MEDIUM. This has the same result as running myisamchk --medium-check tbl_name on the table. The default check type also is MEDIUM for static-format MyISAM tables, unless CHANGED or FAST is specified. In that case, the default is QUICK. The row scan is skipped for CHANGED and FAST because the rows are very seldom corrupted.

You can combine check options, as in the following example that does a quick check on the table to determine whether it was closed properly:


CHECK TABLE may change the table if the table is marked as corrupted or not closed properly but CHECK TABLE does not find any problems in the table. In this case, CHECK TABLE marks the table as okay.

If a table is corrupted, the problem is most likely in the indexes and not in the data part. All of the preceding check types check the indexes thoroughly and should thus find most errors.

If you just want to check a table that you assume is okay, you should use no check options or the QUICK option. The latter should be used when you are in a hurry and can take the very small risk that QUICK does not find an error in the data file. (In most cases, under normal usage, MySQL should find any error in the data file. If this happens, the table is marked as corrupted and cannot be used until it is repaired.)

FAST and CHANGED are mostly intended to be used from a script (for example, to be executed from cron) if you want to check tables from time to time. In most cases, FAST is to be preferred over CHANGED. (The only case when it is not preferred is when you suspect that you have found a bug in the MyISAM code.)

EXTENDED is to be used only after you have run a normal check but still get strange errors from a table when MySQL tries to update a row or find a row by key. This is very unlikely if a normal check has succeeded.

Use of CHECK TABLE ... EXTENDED might influence the execution plan generated by the query optimizer.

Some problems reported by CHECK TABLE cannot be corrected automatically:

InnoDB Details

The following notes apply to InnoDB tables: