使用分组查询学生相关信息和限定条件的分组查询

一、上机练习一

1--查询每门课程的平均分，并按照降序排列

select GradeId,SUM(ClassHour) as 总学时数
from Subject
group by GradeId
order by sum(ClassHour)

2--查询每个参加考试的学员平均分

select studentno,AVG(studentresult) as 平局分
from Result
group by StudentNo

3--查询每门课程的平均分，并按照降序排列

select subjectid,AVG(studentresult)as 平均分
from Result
group by SubjectId
order by 平均分 desc

4--查询每个学生参加所有考试的总分，并按照降序排列

select studentno,SUM(studentresult) as 总分
from Result
group by StudentNo
order by 总分 desc

二、上机练习二

1--查询每年级学时数超过50 的课程数 S1 

select gradeid,COUNT(subjectid) as 课程数
from Subject
where  ClassHour>50
group by GradeId

2--查询每年级学生的平均年龄:

select gradeid,AVG(DATEDIFF(yy,birthday,GETDATE())) as 平均年龄
from student
group by gradeid

3--查询每个年级包含北京的学生

select gradeid,COUNT(1) as 总人数
from student
where address like '%北京%'
group by Gradeid

4--查询参加考试的学生中，平均分及格的学生记录(学号，平均分)，按照降序排列

select studentno,AVG(StudentResult) as 平均分
from Result
group by StudentNo
having AVG(StudentResult)>=60
order by 平均分 desc

5--查询考试时间为2009-9-9课程的及格平均分 

select subjectid,AVG(studentresult) as 平均分
from Result
where ExamDate>='2009-9-9' and  ExamDate<'2009-9-10'
group by SubjectId
having AVG(StudentResult)>=60

6--统计至少有一次不及格的学生学号和次数。

select studentno,COUNT(1) as  次数
from Result
where StudentResult<60
group by StudentNo