(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：/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！
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