drop table if exists t1; CREATE TABLE t1 (id CHAR(12) not null, PRIMARY KEY (id)); insert into t1 values ('000000000001'),('000000000002'); explain select * from t1 where id=000000000001; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index PRIMARY PRIMARY 12 NULL 2 Using where; Using index select * from t1 where id=000000000001; id 000000000001 delete from t1 where id=000000000002; select * from t1; id 000000000001 drop table t1; SELECT 'a' = 'a '; 'a' = 'a ' 1 SELECT 'a\0' < 'a'; 'a\0' < 'a' 1 SELECT 'a\0' < 'a '; 'a\0' < 'a ' 1 SELECT 'a\t' < 'a'; 'a\t' < 'a' 1 SELECT 'a\t' < 'a '; 'a\t' < 'a ' 1 CREATE TABLE t1 (a char(10) not null); INSERT INTO t1 VALUES ('a'),('a\0'),('a\t'),('a '); SELECT hex(a),STRCMP(a,'a'), STRCMP(a,'a ') FROM t1; hex(a) STRCMP(a,'a') STRCMP(a,'a ') 61 0 0 6100 -1 -1 6109 -1 -1 61 0 0 DROP TABLE t1; SELECT CHAR(31) = '', '' = CHAR(31); CHAR(31) = '' '' = CHAR(31) 0 0 SELECT CHAR(30) = '', '' = CHAR(30); CHAR(30) = '' '' = CHAR(30) 0 0 create table t1 (a tinyint(1),b binary(1)); insert into t1 values (0x01,0x01); select * from t1 where a=b; a b Warnings: Warning 1292 Truncated incorrect DOUBLE value: '\x01' select * from t1 where a=b and b=0x01; a b Warnings: Warning 1292 Truncated incorrect DOUBLE value: '\x01' drop table if exists t1; CREATE TABLE t1 (b int(2) zerofill, c int(2) zerofill); INSERT INTO t1 (b,c) VALUES (1,2), (1,1), (2,2); SELECT CONCAT(b,c), CONCAT(b,c) = '0101' FROM t1; CONCAT(b,c) CONCAT(b,c) = '0101' 0102 0 0101 1 0202 0 EXPLAIN EXTENDED SELECT b,c FROM t1 WHERE b = 1 AND CONCAT(b,c) = '0101'; id select_type table type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 100.00 Using where Warnings: Note 1003 select `test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where `test`.`t1`.`b` = 1 and concat(`test`.`t1`.`b`,`test`.`t1`.`c`) = '0101' SELECT b,c FROM t1 WHERE b = 1 AND CONCAT(b,c) = '0101'; b c 01 01 CREATE TABLE t2 (a int); INSERT INTO t2 VALUES (1),(2); SELECT a, (SELECT COUNT(*) FROM t1 WHERE b = t2.a AND CONCAT(b,c) = CONCAT('0',t2.a,'01')) x FROM t2 ORDER BY a; a x 1 1 2 0 EXPLAIN EXTENDED SELECT a, (SELECT COUNT(*) FROM t1 WHERE b = t2.a AND CONCAT(b,c) = CONCAT('0',t2.a,'01')) x FROM t2 ORDER BY a; id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY t2 ALL NULL NULL NULL NULL 2 100.00 Using filesort 2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 3 100.00 Using where Warnings: Note 1276 Field or reference 'test.t2.a' of SELECT #2 was resolved in SELECT #1 Note 1276 Field or reference 'test.t2.a' of SELECT #2 was resolved in SELECT #1 Note 1003 /* select#1 */ select `test`.`t2`.`a` AS `a`,<`test`.`t2`.`a`>((/* select#2 */ select count(0) from `test`.`t1` where `test`.`t1`.`b` = `test`.`t2`.`a` and concat(`test`.`t1`.`b`,`test`.`t1`.`c`) = concat('0',`test`.`t2`.`a`,'01'))) AS `x` from `test`.`t2` order by `test`.`t2`.`a` DROP TABLE t1,t2; CREATE TABLE t1 (a TIMESTAMP); INSERT INTO t1 VALUES (NOW()),(NOW()),(NOW()); SELECT * FROM t1 WHERE a > '2008-01-01' AND a = '0000-00-00'; a DROP TABLE t1; End of 5.0 tests CREATE TABLE t1(a INT ZEROFILL); SELECT 1 FROM t1 WHERE t1.a IN (1, t1.a) AND t1.a=2; 1 DROP TABLE t1; CREATE TABLE t1 (a char(2), index (a)); insert into t1 values ("aa"),("bb"); select * from t1 where a="aa"; a aa select * from t1 where a="aaa"; a select * from t1 where a="aa "; a aa select * from t1 where a>="aaa"; a bb explain select * from t1 where a="aaa"; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ref a a 3 const 1 Using where; Using index explain select * from t1 where a="aa "; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ref a a 3 const 1 Using where; Using index drop table t1;