WHERE DEPT_NO IS NOT
SELECT DEPT_NO, AVG (CURRENT_DATE - EMP_BDATE)
FROM EMP
WHERE DEPT_NO IS NOT NULL
GROUP BY DEPT_NO
HAVING AVG (CURRENT_DATE - EMP_BDATE) <= ALL
(SELECT AVG (CURRENT_DATE - EMP_BDATE)
FROM EMP
WHERE DEPT_NO IS NOT NULL
GROUP BY DEPT_NO);
