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MySQL 四种连接和多表查询详解

Admin MySQL 2021-08-15 11:08:25 95

MySQL 内连接、左连接、右连接、外连接、多表查询

构建环境:

create table t_emp(
	id int primary key, 
	name varchar(20),
	deptId int
);
create table t_dept(
	id int primary key,
	name varchar(20)
);
insert into t_dept(id, name) values(1, '设计部');
insert into t_dept(id, name) values(2, '开发部');
insert into t_dept(id, name) values(3, '测试部');
insert into t_emp(id, name, deptId) values(1, '张三', 1);
insert into t_emp(id, name, deptId) values(2, '李四', 2);
insert into t_emp(id, name, deptId) values(3, '王五', 0);
# ps:为了说明方便,t_emp 表 说成 A 表, t_dept 表说成 B 表

目录

一、INNER JION 内连接 ( A ∩ B )

SELECT * FROM t_emp e INNER JOIN t_dept d ON  e.deptId = d.id;

二、LEFT JOIN 左外连接( A 全有 )

SELECT * FROM t_emp e LEFT JOIN t_dept d ON e.deptId = d.id;

三、RIGHT JOIN 右外连接 (B 全有)

SELECT * FROM t_emp e RIGHT JOIN t_dept d ON e.deptId = d.id;

四、FULL JOIN 全外连接( A + B)

SELECT * FROM t_emp e LEFT JOIN t_dept d 
ON e.deptId = d.id UNION 
SELECT * FROM t_emp e RIGHT JOIN t_dept d ON e.deptId = d.id;

五、LEFT Excluding JOIN ( A - B 即 A 表独有)+

SELECT * FROM t_emp e LEFT JOIN t_dept d ON e.deptId= d.id WHERE d.id is null;

六、RIGHT Excluding JOIN ( B - A 即 B表独有)

SELECT * FROM t_emp e RIGHT JOIN t_dept d ON e.deptId= d.id WHERE e.id is null;

七、OUTER Excluding JOIN (A 与 B 各自独有)

SELECT * FROM t_emp e LEFT JOIN t_dept d ON e.deptId= d.id WHERE d.id is null
UNION
SELECT * FROM t_emp e RIGHT JOIN t_dept d ON e.deptId= d.id WHERE e.id is null;

总结

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