对于教学数据库的三个基本表:S(Sno,Sname,Ssex),SC(Sno,Cno,Grade),C(Cno,Cname, Teacher),

对于教学数据库的三个基本表：S(Sno，Sname，Ssex)，SC(Sno，Cno，Grade)，C(Cno，Cname， Teacher)，其中S为学生表，SC为学生选课表，C为课程表，则对于语句：检索至少选修LIU老师所授课课程中一门课程的女生姓名，SQL语句错误的是______。

A) SELECT Sname

FROM S，SC，C

WHERE S.Sno=SC.Sno AND SC.Cno=C.Cno AND Teacher=‘LIU’AND Ssex=‘F’

B) SELECT Sname

FROM S WHERE Ssex=‘F’AND Sno IN

(SELECT Sno

FROM SC

WHERE Cno IN(SELECT Cno FROM C

WHERE Teacher=‘LIU’))

C) SELECT Sname

FROM S WHERE Ssex=‘F’AND EXISTS (SELECT*

FROM SC

WHERE SC.Sno=S.Sno AND EXISTS

(SELECT*

FROM C

WHERE Teacher=‘LIU’))

D) SELECT Sname

FROM S WHERE Ssex=‘F’AND EXISTS(SELECT*

FROM SC

WHERE SC.Sno=S.Sno AND EXISTS

(SELECT*

FROM C

WHERE C.Cno=SC.Cno AND Teacher=‘LIU’))

C (22) [答案] C