2과목) 다음 SQL 중 실행 결과가 다른 것은?

SELECT COUNT(*) FROM EMP WHERE DEPTNO = 40; SELECT COUNT(COMM) FROM EMP WHERE DEPTNO = 40; SELECT SUM(1) FROM EMP WHERE DEPTNO = 40; SELECT NVL(COUTN(1), 0) FROM EMP WHERE DEPTNO = 40;