Mysql inner join on的用法实例(必看)

Nice MySql

2022-05-22 0 521

语法规则

SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2 
ON table_name1.column_name=table_name2.column_name

先创建两个表，1.用户，2.用户类别

用户表

CREATE TABLE `user` (
 `id` int(32) NOT NULL AUTO_INCREMENT,
 `name` varchar(16) NOT NULL,
 `kindid` int(32) NOT NULL,
 PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

用户类别表

CREATE TABLE `userkind` (
 `id` int(32) NOT NULL AUTO_INCREMENT,
 `kindname` varchar(16) NOT NULL,
 PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

插入一些数据到user表

INSERT INTO `user` VALUES (1,’小明’,1),(2,’小红’,1),(3,’涵涵’,2);插入一些数据到 userkind表

INSERT INTO `userkind` VALUES (1,’普通会员’),(2,’VIP会员’);

如图：

Mysql inner join on的用法实例(必看)

下面是控制台的查询例子：

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mysql> use join;
Database changed
mysql> select * from `user`;
+----+------+--------+
| id | name | kindid |
+----+------+--------+
| 1 | 小明 |   1 |
| 2 | 小红 |   1 |
| 3 | 涵涵 |   2 |
+----+------+--------+
3 rows in set (0.00 sec)

mysql> select * from `userkind`;
+----+----------+
| id | kindname |
+----+----------+
| 1 | 普通会员 |
| 2 | VIP会员 |
+----+----------+
2 rows in set (0.00 sec)

mysql> select * from `user` inner join `userkind` on user.kindid=userkind.id;
+----+------+--------+----+----------+
| id | name | kindid | id | kindname |
+----+------+--------+----+----------+
| 1 | 小明 |   1 | 1 | 普通会员 |
| 2 | 小红 |   1 | 1 | 普通会员 |
| 3 | 涵涵 |   2 | 2 | VIP会员 |
+----+------+--------+----+----------+
3 rows in set (0.02 sec)

mysql> select `id` as `用户ID`,`name` as `用户名`,`kindname` as `用户类别` from
`user` inner join `userkind` where user.kindid=userkind.id;
ERROR 1052 (23000): Column 'id' in field list is ambiguous
mysql> select `user`.`id` as `用户ID`,`name` as `用户名`,`kindname` as `用户类别
` from
  -> `user` inner join `userkind` where `user`.`kindid`=`userkind`.`id`;
+--------+--------+----------+
| 用户ID | 用户名 | 用户类别 |
+--------+--------+----------+
|   1 | 小明  | 普通会员 |
|   2 | 小红  | 普通会员 |
|   3 | 涵涵  | VIP会员 |
+--------+--------+----------+
3 rows in set (0.00 sec)

mysql> select `user`.`id` as `用户ID`,`name` as `用户名`,`kindname` as `用户类别
` from `user` inner join `userkind` on `user`.`kindid`=`userkind`.`id`;
+--------+--------+----------+
| 用户ID | 用户名 | 用户类别 |
+--------+--------+----------+
|   1 | 小明  | 普通会员 |
|   2 | 小红  | 普通会员 |
|   3 | 涵涵  | VIP会员 |
+--------+--------+----------+
3 rows in set (0.00 sec)

mysql>

需要注意的是： 这里的on 基本等价于where(本人感觉)

当 column （字段）两个表都有却分不清时，需要用`表名`.`字段名` 进行分辨。

as就是取别名了。看上面例子就知道！

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