sqlserver: 范围分组查询group by, case

需求：查询在指定年龄段的人数

select case when age>1 and age <26  then 1
 when age>25 and age <27 then 2
              else 0 end as stage,count(*) as population from student 


group by case when age>1 and age <26  then 1
 when age>25 and age <27 then 2

              else 0 end

结果

        stage   population

1        1             2

2        2             5

可通过stage的值区分该条记录是属于哪个年龄段