|
MariaDB [market]> select * from userprofile; # 查询userprofile数据表中的所有记录
+----+------+-----+
| id | name | sex |
+----+------+-----+
| 3 | HPC | 1 |
| 5 | XJ | 1 |
| 6 | LB | 2 |
+----+------+-----+
3 rows in set (0.00 sec)
MariaDB [market]> select * from user_order; # 查询user_order数据表中的所有记录
+------+------+----------+-------+
| o_id | u_id | username | money |
+------+------+----------+-------+
| 2 | 6 | LB | 146 |
| 3 | 3 | HPC | 256 |
| 5 | 5 | XJ | 345 |
+------+------+----------+-------+
3 rows in set (0.01 sec)
2.2 方法二：通过alter table创建外键和级联更新，级联删除
语法：
alter table 数据表名称 add
[constraint [约束名称] ] foreign key (外键字段,..) references 数据表(参照字段,...)
[on update cascade|set null|no action]
[on delete cascade|set null|no action]
)
例子：
MariaDB [market]> create table user_order1(o_id int(11) auto_increment,u_id int(11) default "0",username varchar(50),money int(11),primary key(o_id),index(u_id)); # 创建user_order1数据表，创建表时不使用外键约束
Query OK, 0 rows affected (0.11 sec)
MariaDB [market]> show create table user_order1; # 查看user_order1数据表的创建信息，没有外键约束
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user_order1 | CREATE TABLE `user_order1` (
`o_id` int(11) NOT NULL AUTO_INCREMENT,
`u_id` int(11) DEFAULT '0',
`username` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
`money` int(11) DEFAULT NULL,
PRIMARY KEY (`o_id`),
KEY `u_id` (`u_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec) （编辑：西安站长网）
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