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●Let R and S be the relation respection respectively:Relation R:A B C Relation S:B C D1 2

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●Let R and S be the relation respection respectively：

Relation R:A B C Relation S:B C D

1 2 3 2 3 4

6 7 8 2 3 5

9 7 8 7 8 1

The number of tuples that the result of the expression R∞S(Here if natural join of relations R and S) is (69) ．

(69) A．1

B．4

C．7

D．10

参考答案:

B【解析】译文：关系R和S分别是关系R:A B C,关系S:B C D。表达式R∞S(这里式R、S的自然连接)的结果的元组个数为4。

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