mysql 创建外键sql语句、（例子测试验证MySQL创建外键CREATE TABLE Members (???? Member_ID INT NOTNULL,??
mysql 创建外键sql语句、（例子测试验证
MySQL创建外键
CREATE TABLE Members (
???? Member_ID INT NOTNULL,
????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
);
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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
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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 | 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：
CODE:[Copy to clipboard]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！
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mysql 创建外键sql语句
2008-4-8 10:52
提问者： cly_apple | 浏览次数：3048次
create table UserInfo(??????????????????????
???User_nID???????????? int????????????????? not null,? -- identity
?? User_sNo???????????? varchar(50)????????? null,????? -- 编号
?? User_sName?????????? varchar(50)????????? null,????? -- 名称
?? User_sEmail????????? varchar(200)???????? null,????? -- 邮件
primary key (User_nID)??????????????? -- 设置 主键为 User_nID
)
?
create table OrderInfo(?????????????
???Order_nID???????????? int????????????????? not null,? -- identity
?? Order_UsernID???????? int????????????????? null,????? -- user_nID FK
?? Order_sNo???????????? varchar(50)????????? null,????? -- 编号
?? Order_sPName????????? varchar(50)????????? null,????? -- 项目名称
primary key (Order_nID)??????????????? -- 设置 主键为 User_nID
)
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俩表联系 怎么给 OrderInfo 创建外键？？？
我来帮他解答
输入内容已经达到长度限制
还能输入?9999?字
插入图片删除图片插入地图删除地图插入视频视频地图
参考资料：提交回答取消
2008-4-8 10:56
满意回答
alter table OrderInfo
??????? add constraint FK3C0469F99FC6869
??????? foreign key (userID)
??????? references UserInfo;
FK3C0469F99FC6869 这个是外键名称，自己起
?
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或者
ALTER TABLE bbsReply ADD CONSTRAINT FK_bbsReply_bbsSection FOREIGN KEY? (RSID)
REFERENCES bbsSection (SID),
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