A.Itfailsifanyexistingrowviolatestheconstraint.
B.Itdoesnotvalidatetheexistingdatainthetable.
C.Itenablestheconstrainttobeenforcedattheendofeachtransaction.
D.Itpreventsinsert，update，anddeleteoperationsonthetablewhiletheconstraintisintheprocessofbeingenabled.
正确答案：参考A, D
