MySQL 四种连接和多表查询详解
目录
-
MySQL内连接、左连接、右连接、外连接、多表查询
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构建环境:一、INNERJION内连接(A∩B)二、LEFTJOIN左外连接(A全有)三、RIGHTJOIN右外连接(B全有)四、FULLJOIN全外连接(A+B)五、LEFTExcludingJOIN(A-B即A表独有)+六、RIGHTExcludingJOIN(B-A即B表独有)七、OUTERExcludingJOIN(A与B各自独有)
总结
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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