A.PRIMARY KEYB.FOREION KEYC.FOREIGN KEY (ORDERID) REFERENCES ORDERSD.FOREIGN KEY (BID)
A．PRIMARY KEY
B．FOREION KEY
C．FOREIGN KEY (ORDERID) REFERENCES ORDERS
D．FOREIGN KEY (BID) REFERENCES BOOKS
解析：每张订单具有惟一的订单编号，所以订单编号即为“订单”实体的主键；每张订单编号中可包含多种书籍，但每种书籍的编号仅允许出现一次，所以其主键为(Orderid，Bid)。ORDERLIST的主键为(Orderid，Bid)，所以在CREATE语句中应有PRIMARYKEY(ORDERID,BID);外键为ORDERID和BID，分别参考"ORDER"中的ORDERID和"BOOKS"中的BID，所以在ORDERLIST的创建语句中还应有“FOREIGNKEY(ORDERID)REFERENCESORDERS(ORDERID)”和“FOREIGNKEY(BID)REFERENCESBOOKS(BID)”。
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