Let R and S be the relation respectively: Relation R: A B C Relation S: B C D 1 2 3 2 3 4
题目
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
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