(一)利用外键实现级联删除

1、先建立测试数据库

CREATE TABLE `roottb` (

`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

`data` VARCHAR(100) NOT NULL DEFAULT '',

PRIMARY KEY (`id`)

) TYPE=InnoDB;

CREATE TABLE `subtb` (

`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

`rootid` INT(11) UNSIGNED NOT NULL DEFAULT '0',

`data` VARCHAR(100) NOT NULL DEFAULT '',

PRIMARY KEY (`id`),

INDEX (`rootid`),

FOREIGN KEY (`rootid`) REFERENCES roottb(`id`) ON DELETE CASCADE

) TYPE=InnoDB;

注意：数据表必须使用InnoDB引擎。

外键必须建立索引

外键绑定关系使用了“ on delete cascade ”

2、插入测试数据

INSERT INTO `roottb` (`id`,`data`)

VALUES ('1', 'test root line 1'),

('2', 'test root line 2'),

('3', 'test root line 3');

INSERT INTO `subtb` (`id`,`rootid`,`data`)

VALUES ('1', '1', 'test sub line 1 for root 1'),

('2', '1', 'test sub line 2 for root 1'),

('3', '1', 'test sub line 3 for root 1'),

('4', '2', 'test sub line 1 for root 2'),

('5', '2', 'test sub line 2 for root 2'),

('6', '2', 'test sub line 3 for root 2'),

('7', '3', 'test sub line 1 for root 3'),

('8', '3', 'test sub line 2 for root 3'),

('9', '3', 'test sub line 3 for root 3');

3、查看数据表的状态

4、试验级联删除功能

只删除roottb表中id为2的数据记录，看看subtb表中rootid为2的相关子纪录是否会自动删除！

mysql>; delete from `roottb` where `id`='2';

Query OK, 1 row affected (0.03 sec)

mysql>; select * from `roottb`;

+----+------------------+

| id | data |

+----+------------------+

| 1 | test root line 1 |

| 3 | test root line 3 |

+----+------------------+

2 rows in set (0.00 sec)

mysql>; select * from `subtb`;

+----+--------+----------------------------+

| id | rootid | data |

+----+--------+----------------------------+

| 1 | 1 | test sub line 1 for root 1 |

| 2 | 1 | test sub line 2 for root 1 |

| 3 | 1 | test sub line 3 for root 1 |

| 7 | 3 | test sub line 1 for root 3 |

| 8 | 3 | test sub line 2 for root 3 |

| 9 | 3 | test sub line 3 for root 3 |

+----+--------+----------------------------+

6 rows in set (0.01 sec)

以上部分转自于：bbs.chinaunix.net/forum.php?mod=viewthread&tid=462977

(二)利用触发器实现级联删除

下面给出实例

1、建立测试数据库

CREATE TABLE `root_trigger` (

`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

`data` VARCHAR(100) NOT NULL DEFAULT '',

PRIMARY KEY (`id`)

);

CREATE TABLE `sub_trigger` (

`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

`rootid` INT(11) UNSIGNED NOT NULL DEFAULT '0',

`data` VARCHAR(100) NOT NULL DEFAULT '',

PRIMARY KEY (`id`)

);

2、插入测试数据

INSERT INTO `root_trigger` (`id`,`data`)

VALUES ('1', 'test root line 1'),

('2', 'test root line 2'),

('3', 'test root line 3');

INSERT INTO `sub_trigger` (`id`,`rootid`,`data`)

VALUES ('1', '1', 'test sub line 1 for root 1'),

('2', '1', 'test sub line 2 for root 1'),

('3', '1', 'test sub line 3 for root 1'),

('4', '2', 'test sub line 1 for root 2'),

('5', '2', 'test sub line 2 for root 2'),

('6', '2', 'test sub line 3 for root 2'),

('7', '3', 'test sub line 1 for root 3'),

('8', '3', 'test sub line 2 for root 3'),

('9', '3', 'test sub line 3 for root 3');

3、建立(级联/同步)删除的触发器

drop trigger if exists t_afterdelete_on_sub;

create trigger t_afterdelete_on_sub

after delete on root_trigger

for each row

begin

delete from sub_trigger where rootid=old.id;

end;

4、删除root_trigger表中的id=2的记录，再查看sub_trigger中rootid=2的记录是否删除

删除成功即实现了，触发器的级联删除！