오라클 조인 삭제

DELETE FROM EMP A
WHERE EXISTS (
SELECT 1
FROM DEPT B
WHERE A.DEPTNO = B.DEPTNO
AND B.DEPTNO = '20'
);

DELETE FROM EMP A
WHERE A.DEPTNO = (
SELECT B.DEPTNO
FROM DEPT B
WHERE A.DEPTNO = B.DEPTNO
AND B.DEPTNO = '20'
);

DELETE FROM EMP A
WHERE (A.DEPTNO, A.ENAME) = (
SELECT B.DEPTNO, B.NAME
FROM DEPT B
WHERE B.DEPTNO = '20'
);