单选题
Let R and S be the relation respectively: Relation R: A B C Relation S: B C D 1 2 3 2 3 4 6 7 8 2 3 5 The number of tuplesthat the result of the expression R ∞ S (Here is the natural join of relations R and S) is
A、
3
B、
4
C、
6
D、
9
【正确答案】
B
【答案解析】
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