主外键表删除数据演示

主外键的表删除数据

CREATE TABLE `p1` (
  `id` int(11) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

CREATE TABLE `f1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `pid` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`),
  CONSTRAINT `f1_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `p1` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8


mysql> insert into p1 values (1,'bayue');
Query OK, 1 row affected (0.03 sec)

mysql> insert into f1 values (1,1);
Query OK, 1 row affected (0.00 sec)

mysql> select * from p1,f1; 
+----+-------+----+------+
| id | name  | id | pid  |
+----+-------+----+------+
|  1 | bayue |  1 |    1 |
+----+-------+----+------+
1 row in set (0.00 sec)

mysql> delete p1,f1 from p1,f1 where p1.id=f1.pid; 
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`ran`.`f1`, CONSTRAINT `f1_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `p1` (`id`))

mysql> explain delete p1,f1 from p1,f1 where p1.id=f1.pid;
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref       | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
|  1 | SIMPLE      | p1    | ALL  | PRIMARY       | NULL | NULL    | NULL      |    1 | NULL  |
|  1 | SIMPLE      | f1    | ref  | pid           | pid  | 5       | ran.p1.id |    1 | NULL  |
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
2 rows in set (0.00 sec)

mysql> delete p1,f1 from f1,p1 where p1.id=f1.pid;
Query OK, 2 rows affected (0.01 sec)

mysql> explain delete f1,p1 from p1,f1 where p1.id=f1.pid;
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref       | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
|  1 | SIMPLE      | p1    | ALL  | PRIMARY       | NULL | NULL    | NULL      |    1 | NULL  |
|  1 | SIMPLE      | f1    | ref  | pid           | pid  | 5       | ran.p1.id |    1 | NULL  |
+----+-------------+-------+------+---------------+------+---------+-----------+------+-------+
2 rows in set (0.00 sec)