sql 查询最高分、最低分和平均分语句
//我们要用就以学生成绩为实例吧
/*
结构
学生表
Student(S#,Sname,Sage,Ssex) --S# 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
--2.课程表
Course(C#,Cname,T#) --C# --课程编号,Cname 课程名称,T# 教师编号
*/
查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
--及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
--方法1
select # [课程编号], [课程名称],
max() [最高分],
min() [最低分],
cast(avg() as decimal(18,2)) [平均分],
cast((select count(1) from SC where C# = # and score >= 60)*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C# = # and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C# = # and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [优良率(%)],
cast((select count(1) from SC where C# = # and score >= 90)*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [优秀率(%)]
from Course m , SC n
where # = #
group by # ,
order by #
--方法2
select # [课程编号], [课程名称],
(select max(score) from SC where C# = #) [最高分],
(select min(score) from SC where C# = #) [最低分],
(select cast(avg(score) as decimal(18,2)) from SC where C# = #) [平均分],
cast((select count(1) from SC where C# = # and score >= 60)*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C# = # and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C# = # and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [优良率(%)],
cast((select count(1) from SC where C# = # and score >= 90)*100.0 / (select count(1) from SC where C# = #) as decimal(18,2)) [优秀率(%)]
from Course m
order by #
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