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【单选题】
根据给定的条件,从一个关系中选出一个或多个构成一个新关系,这种操作称为( )。A.
选择
B.
投影
C.
连接
D.
更新
拍照语音搜题，微信中搜索"皮皮学"使用
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A.
to be wasted
B.
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C.
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D.
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