问题详情

A．SELECT Cno, AVG(Score) FROM SCS GROUP BY Score ORDER BY 2 ,Cno DESC
B．SELECT Cno, AVG(Score)FROM SCS GROUP BY Cno ORDER BY 2 ,Cno DESC
C．SELECT Cno, AVG(Score) FROM SCS WHERE Cno, DESC GROUP BY Score
D．SELECT Cno, AVG(Score)FROM SCS GROU PBY, AVG(Score)ORDER BY,Cno DESC请帮忙给出正确答案和分析，谢谢！