GROUP BY ???

GROUP BY ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????? NULL?????????????????????????????????????????????????????????????????????????????????

????????????????????????GROUP BY?????????????????????????????????????????????

??????

GROUP BY ?????? [ , ?????? ] *

?????? ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ????????????GROUP BY???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

GROUP BY????????????????????????????????????????????????????????????????????????????????????????????????

-- airport??????????????????flights??????
-- flying_times?????????????????????
SELECT AVG (flying_time), orig_airport
FROM Flights
GROUP BY orig_airport

SELECT MAX(city_name), region
FROM Cities, Countries
WHERE Cities.country_ISO_code = Countries.country_ISO_code
GROUP BY region
-- smallint???????????????
SELECT ID, AVG(SALARY)
FROM SAMP.STAFF
GROUP BY ID
-- AVGSALARY???EMPCOUNT?????????DEPTNO??????AS???????????????????????????
-- ?????????OTHERS????????????????????????WORKDEPT??????????????????????????????
SELECT OTHERS.WORKDEPT AS DEPTNO,
AVG(OTHERS.SALARY) AS AVGSALARY,
COUNT(*) AS EMPCOUNT
FROM SAMP.EMPLOYEE OTHERS
GROUP BY OTHERS.WORKDEPT