집합 연산자 사용 시 주의사항

SELECT * FROM DEPT;

SELECT *
FROM(
	SELECT * FROM DEPT WHERE DEPTNO IN (10,20,30)
	UNION ALL
	SELECT * FROM DEPT WHERE DEPTNO IN (10,20,30)
	INTERSECT 
	SELECT * FROM DEPT WHERE DEPTNO IN (30,40,50)
    )
;

SELECT *
FROM(
	SELECT * FROM DEPT WHERE DEPTNO IN (10,20,30)
	UNION ALL
	SELECT * FROM DEPT WHERE DEPTNO IN (10,20,30)
	MINUS  
	SELECT * FROM DEPT WHERE DEPTNO IN (30,40,50)
    )

말그대로 집합 특성을 지니기에 중복이 제거된 상태로 결과를 도출한다.