Mysqlinnerjoinon的用法实例(必看)

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Mysqlinnerjoinon的用法实例(必看)

Mysqlinnerjoinon的用法实例(必看):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

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导读Mysqlinnerjoinon的用法实例(必看):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

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：

下面是控制台的查询例子：

Enter password: ****
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.5.40 MySQL Community Server (GPL)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

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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