DEPT_MNG IS NULL THEN NULL
SELECT DEPT.DEPT_NO,
CASE WHEN DEPT. DEPT_MNG IS NULL THEN NULL
ELSE (SELECT EMP.EMP_NAME
FROM EMP
WHERE EMP.EMP_NO = DEPT.DEPT_MNG),
COUNT(*), MIN(EMP1.EMP_SAL),
MAX(EMP1.EMP_SAL), AVG(EMP1.EMP_SAL)
FROM DEPT, EMP, EMP EMP1
WHERE DEPT.DEPT_NO = EMP1.DEPT_NO
GROUP BY DEPT.DEPT_NO;
