Article edited by dbart 1 year, 9 months ago

Selected Revision
Revision
1467
User
dbart
Date
2010-08-16 15:44
Compare To
Revision
1350
User
dbart
Date
2010-08-13 16:53
Additions Deletions

Answer Diff [256]

== Syntax:

<<code>> ¶
CHECKSUM TABLE tbl_name [, tbl_name] ... [ QUICK | EXTENDED ] ¶
<</code>> ¶

== Description:

<<fixedcode>>CHECKSUM TABLE<</fixedcode>> reports a table checksum. This is very
useful if you want to know if two tables are the same (for example on a master
and slave). ¶

With <<fixedcode>>QUICK<</fixedcode>>, the live table checksum is reported if it is
available, or
<<fixed>>NULL<</fixed <<code>>NULL<</code>> otherwise. This is very fast. A live
checksum is enabled
by specifying the <<fixedcode>>CHECKSUM=1<</fixedcode>> table
option when you
[[create-table|create the table]]; currently, this is supported
only for Aria and
MyISAM tables. ¶

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

If neither <<fixedcode>>QUICK<</fixed>> nor <<fixedcode>> nor <<code>>EXTENDED<</fixedcode>> is
specified, MariaDB returns a live
 checksum if the table storage engine supports
it and scans the table
 otherwise. ¶

For a nonexistent table, <<fixedcode>>CHECKSUM TABLE<</fixedcode>> returns <<fixed>>NULL<</fixed
<<code>>NULL<</code>> and generates a
 warning. ¶

== Differences between MariaDB and MySQL:

<<fixedcode>>CHECKSUM TABLE<</fixedcode>> may give different result as MariaDB doesn't
ignore <<fixed>>NULL<</fixedcode>>NULL<</code>>'s in the columns as MySQL 5.1 does (Future MySQL
versions should calculate checksums the same way as MariaDB). You can get the
'old style' checksum in MariaDB by starting mysqld with the <<fixed
<<code>>--old<</fixedcode>> option. Note however that that the MyISAM and Aria
storage engines in MariaDB are using the new checksum internally, so if you are
using --old, the <<fixed<<code>>--old<</code>>, the <<code>>CHECKSUM<</fixedcode>> command will be
slower as it needs to calculate the checksum row by row.