A.ON DELETE RESTRICT B.ON DELETE CASCADE C.ON DELETE SET NULL D.以上答案都不正確
A.可防止非法數(shù)據(jù)的插入 B.會(huì)帶來(lái)額外的開(kāi)銷 C.刪除主表的數(shù)據(jù)時(shí),需要先刪除從表的數(shù)據(jù) D.以上說(shuō)法都不正確