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设数据库中有以下三张表：sc(sno,cno,grade),course(cno,cname,hours),student(sno,sname,ssex,sage,sdept)。试用SQL语言写出以下查询。（3）查询选课门数超过2门的学生的姓名、平均成绩和选课门数

A. SELECT student.sname 姓名,AVG(sc.grade) 平均成绩,COUNT(sc.sno) 选课门数FROM sc Left JOIN student ON sc.sno = student.sno GROUP BY student.sname HAVING COUNT(distinct sc.sno) >2;

B. SELECT student.sname 姓名,AVG(sc.grade) 平均成绩,COUNT(sc.cno) 选课门数FROM sc Left JOIN student ON sc.sno = student.sno GROUP BY student.sname HAVING COUNT(distinct sc.sno) >2;

C. SELECT student.sname 姓名,AVG(sc.grade) 平均成绩,COUNT(distinct sc.sno) 选课门数FROM sc left JOIN student ON sc.sno = student.sno GROUP BY student.sname HAVING COUNT(sc.sno) >2;

D. SELECT student.sname 姓名,AVG(sc.grade) 平均成绩,COUNT(distinct sc.cno) 选课门数FROM sc LEFT JOIN student ON sc.sno = student.sno GROUP BY student.sname HAVING COUNT(distinct sc.cno) >2;

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统计选课门数应该使用COUNT(distinct sc.cno)