招聘管理系统之数据库二---在MySQL中利用外键实现级联删除
老师讲课真垃圾，记得老师讲过级联什么的，但是她没讲出来，也许根本不会。毕竟她不是专门搞数据库的，还搞c，vb等，以前就更多了还有basic，delphe，pasic等我拼都拼不对的语言。show tables;
+----------------+
| Tables_in_zpgl |
+----------------+
| roles |
| users |
| usersroles |
+----------------+
mysql> select * from users ;
+----+----------+----------+
| id | name | password |
+----+----------+----------+
| 1 | zhangsan | 123 |
| 2 | lisi | 123 |
| 3 | wangwu | 123 |
| 4 | zhaoliu | 123 |
| 5 | wangdan | 123 |
| 6 | sgl | 123 |
+----+----------+----------+
mysql> select * from roles ;
+----+----------+
| id | name |
+----+----------+
| 1 | admin |
| 2 | 问卷管理 |
| 3 | 职位管理 |
| 4 | 简历管理 |
| 5 | 面试管理 |
| 6 | 试题管理 |
+----+----------+
mysql> select * from usersroles ;
+----+--------+----------+--------+----------+
| id | userid | username | roleid | rolename |
+----+--------+----------+--------+----------+
| 1 | 6 | sgl | 1 | admin |
| 2 | 1 | zhangsan | 2 | 问卷管理 |
| 3 | 2 | lisi | 3 | 职位管理 |
| 4 | 3 | wangwu | 4 | 简历管理 |
| 5 | 4 | zhaoliu | 5 | 面试管理 |
| 6 | 5 | wangdan | 6 | 试题管理 |
+----+--------+----------+--------+----------+
我想在项目中赋予管理员删除普通用户表（users）用户时，级联删除usersroles的的相关数据。还好在网上找到一篇相关文章，摘过来参考一下（一下是转的）：
首先，目前在产品环境可用的MySQL版本（指4.0.x和4.1.x）中，只有InnoDB引擎才允许使用外键，所以，我们的数据表必须使用InnoDB引擎。
下面，我们先创建以下测试用数据库表：
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：
1、必须使用InnoDB引擎；
2、外键必须建立索引（INDEX）；
3、外键绑定关系这里使用了“ ON DELETE CASCADE”，意思是如果外键对应数据被删除，将关联数据完全删除，更多信息请参考MySQL手册中关于InnoDB的文档；
好，接着我们再来插入测试数据：
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');
我们先看一下当前数据表的状态：
mysql>; show tables;
+----------------+
| Tables_in_test |
+----------------+
| roottb |
| subtb |
+----------------+
2 rows in set (0.00 sec)
mysql>; select * from `roottb`;
+----+------------------+
| id | data |
+----+------------------+
| 1 | test root line 1 |
| 2 | test root line 2 |
| 3 | test root line 3 |
+----+------------------+
3 rows in set (0.05 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 |
| 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 |
+----+--------+----------------------------+
9 rows in set (0.01 sec)
嗯，一切都正常，好，下面我们要试验我们的级联删除功能了。
我们将只删除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)
嗯，看subtb表中对应数据确实自动删除了，测试成功。
结论：在MySQL中利用外键实现级联删除成功！
页:
[1]