用SQL语句检索选修课程在5门以上(含5门)的学生的学号、姓名和平均成绩,并按平均成绩降序排序,正确的命令是( )。
A.SELECT S.学号,姓名,平均成绩FROM S,SC;
WHERE S.学号=SC.学号;
GROUP BY S.学号HAVING COUNT(*)>=5 ORDER BY 平均成绩 DESC
B.SELECT学号,姓名,AVG(成绩)FROM S,SC;
WHERE S.学号=SC.学号 AND COUNT(*)>=5;
GROUPBY 学号 ORDERBY 3 DESC
C.SELECT S.学号,姓名,AVG(成绩) 平均成绩FROM S,SC;
WHERE S.学号=SC.学号 AND COUNT (*)>=5;
GROUP BY S.学号 ORDER BY平均成绩 DESC
D.SELECT S.学号,姓名,AVG(成绩) 平均成绩FROM S,SC;
WHERE S.学号=SC.学号;
GROUP BY S.学号HAVING COUNT(*)>=5 ORDER BY 3 DESC