若对关系R（A，B，C，D）进行π1,3（R）运算，则该关系运算与（此空作答 ）等价，表示（ ）。
- A.见图A
- B.见图B
- C.见图C
- D.见图D
正确答案及解析
正确答案
解析
本题主要考查关系运算。投影运算是从一个关系里面抽取指明的属性（列）组成一个新的关系，这种运算是一种对列进行操作的运算。本题中π1,3（R）的含义就是从关系R中，选取第1列（A）和第3列（C）组成一个新的关系模式，因此52题答案选C，而53题的答案选D。
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