在学生选课数据库中，查询平均成绩大于等于60分的同学，SQL语句为（ ） A: SELECT Sno, AVG(Grade) FROM SC GROUP BY Sno HAVING AVG(Grade)>=60; B: SELECT Sno FROM SC WHERE Grade>=60 GROUP BY Sno; C: SELECT Sno, Grade FROM SC GROUP BY Sno HAVING AVG(Grade)>=60; D: SELECT Sno FROM SC GROUP BY Sno HAVING Grade >=60;

统计选修了a001课程的学生的平均成绩( ) A: select cid,avg(grade) from student group by cid having cid=’a001’ B: select cid,avg(grade) from student where cid=’a001’ group by cid C: select cid,avg(grade) from course where cid=’a001’ group by cid D: select cid,avg(grade) from sc where cid=’a001’ group by cid

查询平均成绩小于70分的学生学号和平均成绩 A: SELECT Sno, AVG(grade) FROM  SC GROUPBYSno B: SELECT Sno, AVG(grade) FROM  SC GROUPBYSno  HAVINGAVG(grade)<70; C: SELECT Sno, grade FROM  SC GROUPBYSno HAVINGAVG(grade)<70;

关系SC(Sno，Cno，Grade)表示学号，课程号，成绩。现要查询平均分在90分以上的学生的学号和平均成绩，正确的语句是______。 A: SELECT Sno，AVG(Grad FROM SC WHERE AVG(Grad＞=90 GROUP BY Sno B: SELECT Sno，AVG(Grad FROM SC GROUP BY Sno HAVING AVG(Grad＞=90 C: SELECT Sno，AVG(Grad FROM SC WHERE AVG(Grad＞=90 ORDER BY Sno D: SELECT Sno，AVG(Grad FROM SC GROUP BY Cno HAVING AVG(Grad＞=90

设关系模式SCG (S#, C#, grade)中S#为学生学号，C#为课程号，grade为某学号学生学某号课程的考试成绩。今要查询每门课程的平均成绩，且要求查询的结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列，则用SQL查询语言应为 (1) 。 若查询的结果仅限于平均分数超过80分的，则应 (2) 。 (1) A: Select C#，AVG(grade) From SCG Group by grade Order by 2，C# Desc B: Select C#，AVG(grade) From SCG Group by C# Order by 2，C# Desc C: Select C#，AVG(grade) From SCG Where C#，AVG Desc Group by grade D: Select C#，AVG(grade) From SCG Group by AVG(grade) Order by 2，C# Desc