mysql欄位約束之外建約束參考操作
1，cascade:從父表刪除或更新且自動刪除或更新子表中匹配的行
格式： on update | delete cascade
2, set null: 從父表刪除或更新，並設定子表中的外來鍵列為null。如果使用該選項必須保證子表列沒有指定not null；
3，rsetrict: 拒絕對附表的刪除或更新操作
4，no action : 標準sql的關鍵字，在mysql中與restrict相同；
1，建立從表
mysql> create table user1(
-> id int unsigned auto_increment primary key,
-> username char(10) not null,
-> cid int unsigned,
-> foreign key (cid) references corse (id) on delete cascade
-> );
query ok, 0 rows affected (0.10 sec)
2，從表自動建立顯示，設定物理外來鍵約束
constraint `user1_ibfk_1` foreign key (`cid`) references `corse` (`id`) on delete cascade
mysql> show create table user1;
| user1 | create table `user1` (
`id` int(10) unsigned not null auto_increment,
`username` char(10) not null,
`cid` int(10) unsigned default null,
primary key (`id`),
key `cid` (`cid`),
constraint `user1_ibfk_1` foreign key (`cid`) references `corse` (`id`) on del
ete cascade
) engine=innodb default charset=utf8 |
3，主表插入屬性值；
mysql> select * from corse;
+----+------------+
| id | name |
+----+------------+
| 1 | shuaishuai |
| 2 | shuaige |
| 3 | shuaibi |
| 4 | dashuai |
+----+------------+
4 rows in set (0.00 sec)
4，從表插入屬性值；
mysql> select * from user1;
+----+-----------+------+
| id | username | cid |
+----+-----------+------+
| 1 | daxiong | 1 |
| 2 | jingxiang | 2 |
| 3 | jiqimao | 3 |
| 4 | 多啦愛夢 | 4 |
+----+-----------+------+
4 rows in set (0.05 sec),
5，刪除主表中的行值；
mysql> delete from corse where id=1;
6，查詢從表中的變化；對應的外鍵值也被刪除或更新；
mysql> select * from corse;
+----+---------+
| id | name |
+----+---------+
| 2 | shuaige |
| 3 | shuaibi |
| 4 | dashuai |
+----+---------+
3 rows in set (0.00 sec)
mysql> select * from user1;
+----+-----------+------+
| id | username | cid |
+----+-----------+------+
| 2 | jingxiang | 2 |
| 3 | jiqimao | 3 |
| 4 | 多啦愛夢 | 4 |
+----+-----------+------+
3 rows in set (0.00 sec)
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