mysql中foreign key的使用注意

mysql> create table orders (id int(11) primary key ,userId int(11) ,  FOREIGN KEY (userId) REFERENCES user(id) );

Query OK, 0 rows affected, 2 warnings (0.06 sec)

mysql> insert orders values(1,3);

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`t`.`orders`, CONSTRAINT `orders_ibfk_1` FOREIGN KEY (`userId`) REFERENCES `user` (`id`))

mysql> insert orders values(1,1);

Query OK, 1 row affected (0.01 sec)