2. 计算机
  3. In order to get names of schoolboys(SEX=’M’)whose age=22, from a relation S(SNO,SNAME,SEX,AGE),which of the following expression

In order to get names of schoolboys(SEX=’M’)whose age=22, from a relation S(SNO,SNAME,SEX,AGE),which of the following expression

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问题 In order to get names of schoolboys(SEX=’M’)whose age=22, from a relation S(SNO,SNAME,SEX,AGE),which of the following expressions is (are) correct?
Ⅰ.πsname( σsex=’M’^age=22(S))  
Ⅱ.σsex=,M,^age=22(πsname(S))
选项 A、Ⅰ only
B、Ⅱ only
C、Ⅰ and Ⅱ
D、neither
答案A
解析
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笔试

原NCRE全国计算机四级

NCRE全国计算机四级

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