MySQL Reference Manual :: 13.5.2.3 CHECK TABLE Syntax

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

option = {QUICK | FAST | MEDIUM | EXTENDED | CHANGED}

Checks a table or tables for errors. CHECK TABLE works for MyISAM and InnoDB tables. For MyISAM tables, the key statistics are updated.

As of MySQL 5.0.2, CHECK TABLE also can check views for problems, such as tables that are referenced in the view definition that no longer exist.

The CHECK TABLE statement returns a table with the following columns:

Note that 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 you should normally run a repair of the table. See Section 5.8.3, “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.

The different check options that can be given are shown in the following table. These options apply only to checking MyISAM tables and are ignored for InnoDB tables and views.

If none of the options QUICK, MEDIUM, or EXTENDED are specified, the default check type for dynamic-format MyISAM tables is MEDIUM. This is the same thing 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, which does a quick check on the table to see whether it was closed properly:

CHECK TABLE test_table FAST QUICK;

Note: In some cases, CHECK TABLE changes the table. This happens if the table is marked as ``corrupted'' or ``not closed properly'' but CHECK TABLE doesn't find any problems in the table. In this case, CHECK TABLE marks the table as okay.

If a table is corrupted, it's most likely that the problem is 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 doesn't find an error in the data file. (In most cases, MySQL should find, under normal usage, any error in the data file. If this happens, the table is marked as ``corrupted'' and cannot be used until it's 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 your table from time to time. In most cases, FAST is to be preferred over CHANGED. (The only case when it isn't 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!)

Some problems reported by CHECK TABLE can't be corrected automatically: