Story of Hyun

-- UNION : 합집합, 선택 데이터를 한개씩만 선택

select deptno from emp

union

select deptno from dept;

-- UNION ALL : 모든 데이터 선택

select deptno from emp

union all

select deptno from dept;

-- INTERSECT : 공통 데이터만 선택

select deptno from emp

intersect

select deptno from dept;

-- MINUS 

select deptno from dept

minus

select deptno from emp;