Hi All, I've a question on kind of delete on whose we have performance issues. Consider two tables: CREATE TABLE `gapfl` ( `pgegapfl` varchar(150) COLLATE utf8_bin NOT NULL, `blkgapfl` varchar(30) COLLATE utf8_bin NOT NULL, `fldgapfl` varchar(30) COLLATE utf8_bin NOT NULL, `ordgapfl` int(11) NOT NULL, ... `stlgapfl` varchar(30) COLLATE utf8_bin DEFAULT NULL, UNIQUE KEY `gapfl_fld` (`pgegapfl`,`blkgapfl`,`fldgapfl`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin and CREATE TABLE `gapge` ( `nuugapge` varchar(150) COLLATE utf8_bin NOT NULL, `nuigapge` int(11) NOT NULL, `frmgapge` varchar(30) COLLATE utf8_bin NOT NULL, `prsgapge` varchar(60) COLLATE utf8_bin NOT NULL, `typgapge` varchar(2) COLLATE utf8_bin NOT NULL, `catgapge` varchar(1) COLLATE utf8_bin NOT NULL, `numgapge` int(11) NOT NULL, `aplgapge` varchar(8) COLLATE utf8_bin DEFAULT NULL, `tragapge` varchar(8) COLLATE utf8_bin DEFAULT NULL, ... `mafgapge` varchar(1) COLLATE utf8_bin NOT NULL, UNIQUE KEY `gapge_nuu` (`nuugapge`), UNIQUE KEY `gapge_frm` (`frmgapge`,`prsgapge`,`typgapge`,`numgapge`,`tragapge`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin Table "gapfl " contains 364740 rows Table "gapge " contains 25423 rows The following delete tooks more than 38 seconds to delete 0 rows . DELETE FROM gapfl WHERE pgegapfl IN ( SELECT nuugapge FROM gapge WHERE frmgapge = 'AMCEVA' AND prsgapge = 'QUALIAC.*.*') It explain plan is : +------+--------------------+-------+-----------------+---------------------+-----------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+--------------------+-------+-----------------+---------------------+-----------+---------+------+--------+-------------+ | 1 | PRIMARY | gapfl | ALL | NULL | NULL | NULL | NULL | 356417 | Using where | | 2 | DEPENDENT SUBQUERY | gapge | unique_subquery | gapge_nuu,gapge_frm | gapge_nuu | 452 | func | 1 | Using where | +------+--------------------+-------+-----------------+---------------------+-----------+---------+------+--------+-------------+ It's not really good and I don't understand why the subselect is consider as a "DEPENDENT SUBQUERY" (there is no correlation columns). Now, I convert this delete into a multi_delete : DELETE gapfl FROM gapfl WHERE pgegapfl IN ( SELECT nuugapge FROM gapge WHERE frmgapge = 'AMCEVA' AND prsgapge = 'QUALIAC.*.*') It tooks 0.00 second and it explain plan is : +------+-------------+-------+------+---------------------+-----------+---------+--------------------+------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-------+------+---------------------+-----------+---------+--------------------+------+--------------------------+ | 1 | PRIMARY | gapge | ref | gapge_nuu,gapge_frm | gapge_frm | 274 | const,const | 1 | Using where; Using index | | 1 | PRIMARY | gapfl | ref | gapfl_fld | gapfl_fld | 452 | dvt.gapge.nuugapge | 7 | | +------+-------------+-------+------+---------------------+-----------+---------+--------------------+------+--------------------------+ as expected. Is there any way to have the right plan with single delete ? Or do we must convert all our complex update to multi_update ? Sorry if it's not the right place to post this query. Regards.