关于SQL语言,查询关联多张表出现的,无法返回空值的问题。
用外连接:
SELECT * from PERempms left outer join PERPROMS
on PERPROMS.BRANCH =PERempms.BRANCH
left outer join PEREDUMS
on PEREDUMS.Education_CODE =PERempms.Education
left outer join PERGRDMS
on PERGRDMS.GRADE=PEREMPMS.GRADE