MySQL七种JOIN类型，终于学明白了

MySQL的JOIN大家在日常工作中都用得很多，今天小朱老师就给大家整理了MySQL七种JOIN类型的用法，一起来深入了解一下吧。数据分析优质社群，等你加入哦~

首先创建需要JOIN的两个表：

CREATE TABLE `tbl_emp` (
   `id` INT(11) NOT NULL AUTO_INCREMENT,
   `name` VARCHAR(30) DEFAULT NULL,
   `deptID` VARCHAR(40) DEFAULT NULL,
   PRIMARY KEY (`id`)
) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

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;

我们可以看到数据的呈现：

1、A ∩ B

 SELECT *
 FROM tbl_emp a
 INNER JOIN tbl_dept b # 共有
 ON a.deptID = b.ID

2、A ( = A ∩ B + A* )

 SELECT *
 FROM tbl_emp a
 LEFT JOIN tbl_dept b
 ON a.deptID = b.ID

3、B ( = A ∩ B + B* )

 SELECT *
 FROM tbl_emp a
 RIGHT JOIN tbl_dept b
 ON a.deptID = b.ID

4. A* ( = A - A ∩ B )

 SELECT *
 FROM tbl_emp a
 LEFT JOIN tbl_dept b 
 ON a.deptID = b.ID # ON时主表保留
 WHERE B.ID IS NULL # 筛选A表数据

5. B* ( = B - A ∩ B )

 SELECT *
 FROM tbl_emp a
 RIGHT JOIN tbl_dept b 
 ON a.deptID = b.ID # ON时主表保留
 WHERE a.deptID IS NULL # 筛选B表数据

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


-- MySQL格式
 SELECT *
 FROM tbl_emp a
 LEFT JOIN tbl_dept b 
 ON a.deptID = b.ID 
 UNION
 SELECT *
 FROM tbl_emp a
 RIGHT JOIN tbl_dept b 
 ON a.deptID = b.ID

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


-- MySQL格式
 SELECT *
 FROM tbl_emp a
 LEFT JOIN tbl_dept b 
 ON a.deptID = b.ID 
 UNION
 SELECT *
 FROM tbl_emp a
 RIGHT JOIN tbl_dept b 
 ON a.deptID = b.ID
 WHERE a.deptID IS NULL OR b.ID IS NULL

以上就是其中JOIN类型的介绍，大家可以用起来了哦。