A.SELECT SN,AGE,SEX FROM SWHE RESN=“王華” B.SELECT SN,AGE,SEX FROM SWHE REAGE>(SELECTAGEFROMSWHERESN=“王華”) C.SELECT SN,AGE,SEX FROM SWHE REAGE>(SELECTAGEWHERESN=“王華”) D.SELECT SN,AGE,SEX FROM SWHE REAGE>王華.AGE
A.能惟一決定關系的字段 B.不可改動的專用保留字 C.關鍵的很重要的字段 D.能惟一標識元組的屬性或?qū)傩约?/p>
A.關鍵字 B.數(shù)據(jù)項 C.主屬性 D.主屬性值