Hello.
MySQL uses indexes in queries which are parts of UNION. See: mysql> explain (select * from t1 where a=5) union (select * from t1 where a=3)\G; *************************** 1. row *************************** id: 1 select_type: PRIMARY table: t1 type: ref possible_keys: a key: a key_len: 5 ref: const rows: 1 Extra: Using where; Using index *************************** 2. row *************************** id: 2 select_type: UNION table: t1 type: ref possible_keys: a key: a key_len: 5 ref: const rows: 1 Extra: Using where; Using index *************************** 3. row *************************** id: NULL select_type: UNION RESULT table: <union1,2> type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: NULL Extra: 3 rows in set (0.00 sec) mysql> show create table t1\G; *************************** 1. row *************************** Table: t1 Create Table: CREATE TABLE `t1` ( `a` int(11) default NULL, KEY `a` (`a`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 > Hello, > > MySQL implemented index_merge in version 5... > Does MySQL supports something like index_merge to speed up UNION > queries? If yes, for which version (assumed release time)? > Does anyone know of other DBs systems that can speed up UNION queries? > This issue is quite critical for our system.. > > -thanks in advance. > > > -- For technical support contracts, goto https://order.mysql.com/?ref=ensita This email is sponsored by Ensita.NET http://www.ensita.net/ __ ___ ___ ____ __ / |/ /_ __/ __/ __ \/ / Gleb Paharenko / /|_/ / // /\ \/ /_/ / /__ [EMAIL PROTECTED] /_/ /_/\_, /___/\___\_\___/ MySQL AB / Ensita.NET <___/ www.mysql.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]