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 9 7 8 7 8 1 The number of tuples that the result of the expression R ∞ S( Here is the natural join of relations R and S)is (69) .
【正确答案】
B
【答案解析】[解析] 译文：关系R和S分别是R：A B C，关系S：B C D。表达式 R ∞ S(这里是R、S的自然连接)的结果的元组个数为4。