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在学生选课数据库中,检索被全部学生所选修的课程的SQL可以描述为()
A、SELECT Cno FROM SC WHERE (Select Count(Sno) FROM SC GROUP BY Cno) = (SELECT Count(*) FROM Student) ;
B、SELECT Cno FROM SC x WHERE NOT EXISTS (SELECT * FROM Student s WHERE NOT EXISTS (SELECT * FROM SC y WHERE x.Cno = y.Cno AND s.Sno= y.Sno);
C、SELECT Cno FROM SC x WHERE NOT EXISTS ((SELECT Sno FROM Student) EXCEPT (SELECT y.Sno FROM SC y, Student z WHERE x.Cno=y.Cno AND z.Sno=y.Sno));
D、以上答案都不对
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