-- 准备工作
drop table if exists Emp;
create table if not exists Emp
(
uid int primary key,
sid int
);
insert into Emp values(1,1);
insert into Emp values(2,2);
drop table if exists Sal;
create table if not exists Sal
(
sid int primary key,
salary float
);
insert into Sal values(1,11);
insert into Sal values(3,33);
-- 查看结果
select * from Emp left join Sal on Emp.sid = Sal.sid;
左表为主(左表内容至少全部出现一次)
uid
sid
sid
salary
1
1
1
11
2
2
NULL
NULL
select * from Emp right join Sal on Emp.sid = Sal.sid;
右表为主(右表内容至少全部出现一次)
uid
sid
sid
salary
1
1
1
11
NULL
NULL
3
33
select * from Emp inner join Sal on Emp.sid = Sal.sid;
相当于上面两表求交集
uid
sid
sid
salary
1
1
1
11
原文:/playSCforever/p/3970788.html