MySQL创建外键

CREATE TABLE Members (

???? Member_ID INT NOT NULL,
???? PRIMARY KEY AUTO_INCREMENT,

???? First_Name VARCHAR(30) NOT NULL,

???? Last_Name VARCHAR(30) NOT NULL,
???? Bday DATE NOT NULL,

???? Gender ENUM('M', 'F') DEFAULT 'F'

);

CREATE TABLE Email (

????? Email VARCHAR(50),

????? Member_ID INT NOT NULL,

????? PRIMARY KEY (Email, Member_ID),
????? CONSTRAINT FOREIGN KEY (Member_ID) REFERENCES Members(Member_ID)

????? ON DELETE? RESTRICT? ON UPDATE CASCADE

);

?

在 MySQL 中只有 InnoDB 类型的表才支持外键与存储过程
所有要建立外键的字段必须建立索引

?

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：


CODE:[Copy to clipboard]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：


CODE:[Copy to clipboard]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：


CODE:[Copy to clipboard]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 |