42. 已知二個關聯(relation) R(a, b, c)，S(c, d)，R.c 為一外來鍵(foreign key)，參考 S.c， 下列何者符合此參考整合限制(referential integrity)？
(A) R = {(1, 2, 3), (1, 4, 9), (1, 5, 5)}, S = {(3, 7), (5, 8)}
(B) R = {(1, 2, 3), (1, 4, 9), (1, 5, 6)}, S = {(3, 7), (9, 8)}
(C) R = {(1, 2, 4), (1, 4, 9), (1, 5, 7)}, S = {(4, 7), (7, 8)}
(D) R = {(1, 2, 4), (1, 4, 6), (1, 5, 6)}, S = {(4, 7), (6, 8)}

相關試題

相關試卷