MySQL七种JOIN类型小结

在开始之前，我们创建两个表用于演示将要介绍的其中JOIN类型。

建表

CREATE TABLE `tbl_dept` (

   `id` INT(11) NOT NULL AUTO_INCREMENT,

   `deptName` VARCHAR(30) DEFAULT NULL,

   `locAdd` VARCHAR(40) DEFAULT NULL,

   PRIMARY KEY (`id`)

) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE `tbl_emp` (

   `id` INT(11) NOT NULL AUTO_INCREMENT,

   `name` VARCHAR(20) DEFAULT NULL,

   `deptId` VARCHAR(11) NOT NULL,

   PRIMARY KEY (`id`),

   KEY `fk_dept_id` (`deptId`)

) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;初始化数据

七种JOIN


1. A ∩ B

SELECT < select_list >

FROM TableA A

INNER JOIN TableB B # 共有

ON A.Key = B.Key

2. A ( = A ∩ B + A* )

SELECT < select_list >

FROM TableA A

LEFT JOIN TableB B

ON A.Key = B.Key

3. B ( = A ∩ B + B* )

SELECT < select_list >

FROM TableA A

RIGHT JOIN TableB B

ON A.Key = B.Key

4. A* ( = A – A ∩ B )

SELECT < select_list >

FROM TableA A

LEFT JOIN TableB B

ON A.Key = B.Key # ON时主表保留

WHERE B.Key IS NULL # 筛选A表数据

5. B* ( = B – A ∩ B )

SELECT < select_list >

FROM TableA A

RIGHT JOIN TableB B

ON A.Key = B.Key

WHERE A.Key IS NULL

6. A ∪ B

SELECT < select_list >

FROM TableA A

FULL OUTER JOIN TableB B ## FULL OUTER 仅oracle支持

ON A.Key = B.Key

7. A ∪ B – A ∩ B

SELECT < select_list >

FROM TableA A

FULL OUTER JOIN TableB B

ON A.Key = B.Key

WHERE A.Key IS NULL OR B.Key IS NULL

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