A.(’1031’,’曾華’,男,23) B.(’1031’,’曾華’,NULL,NULL) C.(NULL,’曾華’,’男’,’23’) D.(’1031’,NULL,’男’,23)
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(guān)系的字段 B.不可改動(dòng)的專用保留字 C.關(guān)鍵的很重要的字段 D.能惟一標(biāo)識(shí)元組的屬性或?qū)傩约?/p>