Sql纵向表转为横向表，并分组统计。

在写系统尤其是在写课程系统是经常会遇到类似如下纵-横转换，在使用group by ... with cube/rollup + grouping() 来实现是非常容易做到的。



1. 用于测试的数据如下：

declare @tab table(Class varchar(20),Student varchar(20),Course varchar(50),Grades decimal(7,2));
insert into @tab(Class,Student,Course,Grades) values('A班','张三','语文',60);
insert into @tab(Class,Student,Course,Grades) values('A班','张三','数学',70);
insert into @tab(Class,Student,Course,Grades) values('A班','张三','英语',80);
insert into @tab(Class,Student,Course,Grades) values('A班','李四','语文',30);
insert into @tab(Class,Student,Course,Grades) values('A班','李四','数学',40);
insert into @tab(Class,Student,Course,Grades) values('A班','李四','英语',50);
insert into @tab(Class,Student,Course,Grades) values('B班','王五','语文',65);
insert into @tab(Class,Student,Course,Grades) values('B班','王五','数学',75);
insert into @tab(Class,Student,Course,Grades) values('B班','王五','英语',85);
insert into @tab(Class,Student,Course,Grades) values('B班','赵六','语文',35);
insert into @tab(Class,Student,Course,Grades) values('B班','赵六','数学',45);
insert into @tab(Class,Student,Course,Grades) values('B班','赵六','英语',55);

select * from @tab

2. 实现此效果的SQL语句如下：

select
(case when Grouping(Class)=1 then '总平均' when Grouping(Student)=1 then '' else Class end ) as Class
,(case when Grouping(Class)=1 then '' when Grouping(Student)=1 then '平均' else Student end) as Student
,cast(avg(语文) as decimal(7,2)) as 语文
,cast(avg(数学) as decimal(7,2)) as 数学
,cast(avg(英语) as decimal(7,2)) as 英语
,cast(avg(总分) as decimal(7,2)) as 总分
from (
select Class,Student
,(select isnull(sum(Grades),0) from @tab where Class=t.Class and Student=t.Student and Course='语文') as '语文'
,(select isnull(sum(Grades),0) from @tab where Class=t.Class and Student=t.Student and Course='数学') as '数学'
,(select isnull(sum(Grades),0) from @tab where Class=t.Class and Student=t.Student and Course='英语') as '英语'
,(select isnull(sum(Grades),0) from @tab where Class=t.Class and Student=t.Student) as '总分'
from @tab as t
group by Class,Student
) as tempTab
group by Class,Student,语文,数学,英语,总分 with rollup
having Grouping(语文)=1
and Grouping(数学)=1
and Grouping(英语)=1

这里没有考虑做到通用，如果做到通用可能会比较复杂，也不知道性能会怎么样。