mysql left join,right join,inner join簡單一實例

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-- 準備工作

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);

-- 查看結果
select * from Emp left  join Sal on Emp.sid = Sal.sid;

左表為主（左表內容至少全部出現一次）

uid	sid	sid	salary
1	1	1	11
2	2	NULL	NULL

select * from Emp right join Sal on Emp.sid = Sal.sid;

右表為主（右表內容至少全部出現一次）

uid	sid	sid	salary
1	1	1	11
NULL	NULL	3	33

select * from Emp inner join Sal on Emp.sid = Sal.sid;

相當於上面兩表求交集

uid	sid	sid	salary
1	1	1	11

mysql left join,right join,inner join簡單一實例