SQL 查詢最高分、最低分和平均分語句
我們要用就以學生成績為實例吧
/*
結構
學生表
Student(S#,Sname,Sage,Ssex) --S# 學生編號,Sname 學生姓名,Sage 出生年月,Ssex 學生性別
--2.課程表
Course(C#,Cname,T#) --C# --課程編號,Cname 課程名稱,T# 教師編號
*/
查詢各科成績最高分、最低分和平均分:以如下形式顯示:課程ID,課程name,最高分,最低分,平均分,及格率,中等率,優良率,優秀率
--及格為>=60,中等為:70-80,優良為:80-90,優秀為:>=90
--方法1
select m.C# [課程編號], m.Cname [課程名稱],
max(n.score) [最高分],
min(n.score) [最低分],
cast(avg(n.score) as decimal(18,2)) [平均分],
cast((select count(1) from SC where C# = m.C# and score >= 60)*100.0 / (select count(1) from SC where C# = m.C# ) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where C# = m.C#) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 80 and score < 90 )*100.0 / (select count(1) from SC wher e C# = m.C#) as decimal(18,2)) [優良率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 90)*100.0 / (select count(1) from SC where C# = m.C# ) as decimal(18,2)) [優秀率(%)]
from Course m , SC n
where m.C# = n.C#
group by m.C# , m.Cname
order by m.C#
--方法2
select m.C# [課程編號], m.Cname [課程名稱],
(select max(score) from SC where C# = m.C#) [最高分],
(select min(score) from SC where C# = m.C#) [最低分],
(select cast(avg(score) as decimal(18,2)) from SC where C# = m.C#) [平均分],
cast((select count(1) from SC where C# = m.C# and score >= 60)*100.0 / (select count(1) from SC where C# = m.C# ) as decimal(18,2)) [及格率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 70 and score < 80 )*100.0 / (select count(1) from SC wher e C# = m.C#) as decimal(18,2)) [中等率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where C# = m.C#) as decimal(18,2)) [優良率(%)],
cast((select count(1) from SC where C# = m.C# and score >= 90)*100.0 / (select count(1) from SC where C# = m.C# ) as decimal(18,2)) [優秀率(%)]
from Course m
order by m.C#