意外と知られてなさそうな雰囲気なので書いておきます。 mysql> create table t1 (c1 int, c2 int auto_increment, c3 varchar(100), primary key (c1,c2)); Query OK, 0 rows affected (0.01 sec) mysql> insert into t1 (c1,c3) values (1, "aiueo"); Query OK, 1 row affected (0.00 sec) mysql> insert into t1 (c1,c3) values (1, "aiueo"); Query OK, 1 row affected (0.01 sec) mysql> insert into t1 (c1,c3) values (1, "aiueo"); Query OK, 1 row a