LEFT OUTER JOIN??????

LEFT OUTER JOIN????????????join?????????????????????JOIN???????????????????????? ???????????????????????????(??????)??????????????????????????????????????????(??????)???????????????????????????????????????NULL??????????????????????????????????????????????????????????????????

??????

?????? LEFT [ OUTER ] JOIN ??????
{
    ON ????????? 
    }

ON???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ON????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????(??????????????????????????????????????????)

??? 1

--????????????????????????????????????

SELECT CITIES.COUNTRY, CITIES.CITY_NAME, REGION 
FROM Countries 
LEFT OUTER JOIN Cities
ON CITIES.COUNTRY_ISO_CODE = COUNTRIES.COUNTRY_ISO_CODE
WHERE REGION = 'Asia'

-- LEFT JOIN????????????????????????????????????????????????????????????
-- ???????????????

SELECT  COUNTRIES.COUNTRY, CITIES.CITY_NAME,REGION 
FROM COUNTRIES 
LEFT JOIN CITIES 
ON CITIES.COUNTRY_ISO_CODE = COUNTRIES.COUNTRY_ISO_CODE
WHERE REGION = 'Asia'

??? 2


-- EMPLOYEE???DEPAETMENT??????????????????????????????
-- 1930????????????????????????(BIRTHDATE)?????????????????????
-- ????????????(EMPNO)??????
-- ???????????????(LASTNAME)??????
-- ????????????(EMPLOYEE???????????????WORKDEPT??????DEPARTMENT???????????????DEPTNO)??????
-- ?????????(DEPTNAME)??????????????????

SELECT EMPNO, LASTNAME, WORKDEPT, DEPTNAME 
   FROM SAMP.EMPLOYEE LEFT OUTER JOIN SAMP.DEPARTMENT 
   ON WORKDEPT = DEPTNO 
   AND YEAR(BIRTHDATE) < 1930

-- ?????????????????????????????????????????????????????????
-- ??????????????????????????????????????????????????????????????????

SELECT DEPTNO, DEPTNAME, EMPNO, LASTNAME
      FROM DEPARTMENT LEFT OUTER JOIN EMPLOYEE
	    ON MGRNO = EMPNO
???????????????: JOIN ??????