[데이터 베이스]10.집합

-- 1. union all (통으로 붙인다 컴럼갯수가 동일 해야한다

select sum(sal), deptno
from emp
where deptno =10
union all
select sum(sal), deptno
from emp
where deptno =20
union all
select sum(sal), deptno
from emp
where deptno =30
union all
select sum(sal), null
from emp;

-- 2. union (합집합 - 중복을 제거하고 통으로 붙인다(연산이 든다))
select *
from dept
where deptno > 10 -- 20, 30, 40
union 
select *
from dept
where deptno < 30; -- 10, 20

-- 3. intersect(교집합 - 중복을 붙인다(툴이 오류난거 처럼 보임))
select *
from dept
where deptno > 10 -- 20, 30, 40
intersect
select *
from dept
where deptno < 30; -- 10, 20

-- 4. EXCEPT(차집합 - (툴이 오류난거 처럼 보임))
select *
from dept
where deptno > 10 -- 20, 30, 40
except
select *
from dept
where deptno < 30; -- 10, 20