题目内容:
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 .
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答案解析: