JOIN的七钟实现分为:
1.A,B表共有
select * from t_emp a inner join t_dept b on a.deptId = b.id;
2.A,B两表共有+A的独有:
select * from t_emp a left join t_dept b on a.deptId = b.id;
3.A,B两表共有+B的独有:
select * from t_emp a right join t_dept b on a.deptId = b.id;
4.A的独有:
select * from t_emp a left join t_dept b on a.deptId = b.id where b.id is null;
5.B的独有:
select * from t_emp a right join t_dept b on a.deptId = b.id where a.deptId is null;
6.A,B全有:
SELECT * FROM t_emp A LEFT JOIN t_dept B ON A.deptId = B.id
UNION
SELECT * FROM t_emp A RIGHT JOIN t_dept B ON A.deptId = B.id
7.A的独有+B的独有:
SELECT * FROM t_emp A LEFT JOIN t_dept B ON A.deptId = B.id WHERE B.`id` IS NULL
UNION
SELECT * FROM t_emp A RIGHT JOIN t_dept B ON A.deptId = B.id WHERE A.`deptId` IS NULL;