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MariaDB [market]> select * from user_order; # 查看order表的数据
+------+------+----------+-------+
| o_id | u_id | username | money |
+------+------+----------+-------+
| 2 | 2 | LB | 146 |
| 3 | 3 | HPC | 256 |
+------+------+----------+-------+
3 rows in set (0.00 sec)
2.1.3 测试级联更新
更新数据之前的状态
MariaDB [market]> select * from userprofile; # 查看userprofile表的数据
+----+------+-----+
| id | name | sex |
+----+------+-----+
| 2 | LB | 2 |
| 3 | HPC | 1 |
+----+------+-----+
3 rows in set (0.00 sec)
MariaDB [market]> select * from user_order; # 查看order表的数据
+------+------+----------+-------+
| o_id | u_id | username | money |
+------+------+----------+-------+
| 2 | 2 | LB | 146 |
| 3 | 3 | HPC | 256 |
+------+------+----------+-------+
3 rows in set (0.00 sec)
更新数据
MariaDB [market]> update userprofile set id=6 where id=2; # 把userprofile数据表中id为2的用户改为id为6
Query OK, 1 row affected (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 0
更新数据后的状态
MariaDB [market]> select id,name,sex,money,o_id from userprofile,user_order where id=u_id; # 联表查询，可以看出表中已经没有id为2的用户了
+----+------+-----+-------+------+
| id | name | sex | money | o_id |
+----+------+-----+-------+------+
| 6 | LB | 2 | 146 | 2 |
| 3 | HPC | 1 | 256 | 3 |
+----+------+-----+-------+------+
2 rows in set (0.00 sec)
MariaDB [market]> select * from userprofile; # 查看userprofile表的数据，id只剩下3和6
+----+------+-----+
| id | name | sex |
+----+------+-----+
| 3 | HPC | 1 |
| 6 | LB | 2 |
+----+------+-----+
2 rows in set (0.00 sec)
MariaDB [market]> select * from user_order; # 查看user_order表的数据,u_id也改为6
+------+------+----------+-------+
| o_id | u_id | username | money |
+------+------+----------+-------+
| 2 | 6 | LB | 146 |
| 3 | 3 | HPC | 256 |
+------+------+----------+-------+
2 rows in set (0.00 sec)
2.1.4 测试数据完整性
MariaDB [market]> insert into user_order(u_id,username,money)values(5,"XJ",345); # 单独向user_order数据表中插入数据，插入数据失败
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`market`.`user_order`, CONSTRAINT `user_order_ibfk_1` FOREIGN KEY (`u_id`) REFERENCES `userprofile` (`id`) ON DELETE CASCADE ON UPDATE CASCADE)
在上面的例子中，user_order表的外键约束，user_order表受userprofile表的约束
在user_order里面插入一条数据u_id为5用户，在userprofile表里面根本没有，所以插入数据失败
先向userprofile表中插入记录，再向user_order表中插入记录就可以了
MariaDB [market]> insert into userprofile values(5,"XJ",1); # 先向userprofile数据表中插入id为5的记录，插入数据成功
Query OK, 1 row affected (0.01 sec)
MariaDB [market]> insert into user_order(u_id,username,money) values(5,"XJ",345); # 再向user_order数据表中插入数据,成功
Query OK, 1 row affected (0.00 sec) （编辑：西安站长网）
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