有三个关系R、S和T如下: R:A B C S: a 1 2 A B T: b 2 1 c 3 c c 3 1 1 则由关系R和S得到关系T的操作是
A.
自然连接
B.
交
C.
除
D.
并
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参考答案:
举一反三
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