4.집합 연산자

집합연산자는 두 개 이상의 SELECT문의 결과 값을 연결할 때 사용

집합 연산자의 종류

1. UNION  :  합집합, 중복제거

SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno IN (10, 20)
UNION
SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno=10
ORDER BY deptno;

union 출력값

2. UNION ALL : 합집합, 중복포함

SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno IN (10, 20)
UNION ALL
SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno=10
ORDER BY ename;

3. MINUS : 차집합

SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno IN (10, 20)
MINUS
SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno=10;

4.INTERSECT : 교집합

SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno IN (10, 20)
INTERSECT
SELECT empno, ename, sal, deptno
FROM   emp
WHERE  deptno=10;