a b 1 Testing 2 table 3 t1 1 Testing 2 table 3 t2 a b 3 t1 3 t2 2 table 2 table 1 Testing 1 Testing table type possible_keys key key_len ref rows Extra t3 range a a 4 NULL 10 where used table type possible_keys key key_len ref rows Extra t3 range a a 4 NULL 10 where used a b 10 Testing 10 Testing a b 1 Testing 1 Testing 2 table 2 table 3 t1 3 t2 4 Testing 4 Testing 5 table 5 table 6 t1 6 t2 7 Testing 7 Testing 8 table 8 table 9 t2 9 t2 a b 11 table 11 table 12 t1 12 t1 13 Testing 13 Testing 14 table 14 table 15 t2 15 t2 16 Testing 16 Testing 17 table 17 table 18 t2 18 t2 19 Testing 19 Testing table type possible_keys key key_len ref rows Extra t3 index NULL a 4 NULL 1131 Using index a 699 698 697 696 695 694 693 692 691 690 a 416 415 415 414 414 413 413 412 412 411 Table Create Table t3 CREATE TABLE `t3` ( `a` int(11) NOT NULL default '0', `b` char(20) default NULL, KEY `a` (`a`) ) TYPE=MRG_MyISAM UNION=(t1,t2) c test1 test1 test1 test2 test2 test2 c test1 test1 test1 test2 test2 test2 c c incr othr incr othr 1 10 2 24 4 33 3 53 count(*) 10 count(*) 20 count(*) 20 Table Create Table t3 CREATE TABLE `t3` ( `incr` int(11) NOT NULL default '0', `othr` int(11) NOT NULL default '0', PRIMARY KEY (`incr`) ) TYPE=MRG_MyISAM UNION=(t1,t2) Table Create Table t3 CREATE TABLE `t3` ( `incr` int(11) NOT NULL default '0', `othr` int(11) NOT NULL default '0' ) TYPE=MRG_MyISAM UNION=(t1,t2) a a b 1 1 1 2