问题 单项选择题

(33)~(34)题的关系代数操作基于如下的关系R和S:

查询选修了课程号为’C2’的学号和姓名,若用下列SQL的SELECT语句表达时,哪一个是不正确的 ( )

A.SELECT S#,SNAMEFROMS WHERE S#=(SELECTSS# FROMSC WHERE C#=’C2’

B.SELECTS#,SNAMEFROMS,SC WHERES#=SS# AND C#=’C2’

C.SELECTS#,SNAME FROM S,SC WHERES#=SS# AND C#=’C2’ORDER BY S#

D.SELECTS#,SNAME FROM S WHERE S# IN (SELECT S S# FROM SC WHERE C#=’C2’

答案

参考答案:A

单项选择题
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