--union
--把两个查询结果进行拼接 
--会对重复的数据进行过滤 

select * from emp where deptno in(10,20)
union
select * from emp where deptno = 20;

--union all

--不会过滤 显示两个表中和 13条

select * from emp where deptno in(10,20)
union all
select * from emp where deptno = 20;

--intersect
--求两个查询结果的交集 

select * from emp where deptno in(10,20)
intersect
select * from emp where deptno = 20;

--minus
--第一个查询结果 减去第二查询结果

select * from emp where deptno in(10,20)
minus
select * from emp where deptno = 20;