Question

我有两个表：用户和管理员。

+-------------------------+
| TABLE : user
+-------------------------+
| id: PRIMARY_KEY
| username
| password
+-------------------------+

+-------------------------+
| TABLE: admin
+-------------------------+
| user_id: FOREIGN_KEY
| e-mail
+-------------------------+

管理员也是用户，因此，两个表在1：1的关系中是一起的。当从User表中删除一行时，它也会从表Admin中删除（在admin.user_id设置关系ON DELETE CASCADE），但如果我从表Admin中删除一行怎么办？然后它不会从User表中删除，这会使数据库中的混乱。这有什么解决方案吗？如何在双方制定实现？

Answer 1

将类似的外键添加到admin表 -

ALTER TABLE user
  ADD CONSTRAINT FK_user_admin_user_id FOREIGN KEY (id)
    REFERENCES admin(user_id) ON DELETE CASCADE ON UPDATE RESTRICT;

现在，您可以从user或admin表中删除行，并删除相关记录。

使用 FOREIGN_KEY_CHECKS 变量添加新记录，例如 -

SET FOREIGN_KEY_CHECKS = 0;

INSERT INTO user(id) VALUES(1);
INSERT INTO admin(user_id) VALUES(1);

SET FOREIGN_KEY_CHECKS = 1;

输出的完整示例 -

CREATE TABLE user (
  id int(11) NOT NULL AUTO_INCREMENT,
  username varchar(255) DEFAULT NULL,
  password varchar(255) DEFAULT NULL,
  PRIMARY KEY (id),
  CONSTRAINT FK_user_admin_user_id FOREIGN KEY (id)
  REFERENCES admin (user_id) ON DELETE CASCADE ON UPDATE RESTRICT
)
ENGINE = INNODB;

CREATE TABLE admin (
  user_id int(11) NOT NULL AUTO_INCREMENT,
  `e-mail` varchar(255) DEFAULT NULL,
  PRIMARY KEY (user_id),
  CONSTRAINT FK_admin_user_id FOREIGN KEY (user_id)
  REFERENCES user (id) ON DELETE CASCADE ON UPDATE RESTRICT
)
ENGINE = INNODB;

SET FOREIGN_KEY_CHECKS = 0;

INSERT INTO user(id) VALUES(1);
INSERT INTO user(id) VALUES(2);
INSERT INTO user(id) VALUES(3);

INSERT INTO admin(user_id) VALUES(1);
INSERT INTO admin(user_id) VALUES(2);
INSERT INTO admin(user_id) VALUES(3);

SET FOREIGN_KEY_CHECKS = 1;

DELETE FROM user WHERE id = 1;
DELETE FROM admin WHERE user_id = 2;

SELECT * FROM user;
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  3 | NULL     | NULL     |
+----+----------+----------+

SELECT * FROM admin;
+---------+--------+
| user_id | e-mail |
+---------+--------+
|       3 | NULL   |
+---------+--------+

MySQL中的一对一关系和级联删除

1 个答案: