select '18-20',
    count(case when age between 18 and 20 then 1 end) * 100.0 / count(*)
from employees

union all 

select '26-40',
    count(case when age between 26 and 40 then 1 end) * 100.0 / count(*)
from employees

SQL小提琴示例#1
你也可以写一个稍微干净一点（更容易维护）的版本，如下所示：

select cast(r.Start as varchar(3)) + '-' + cast(r.[End] as varchar(3)),
    count(case when e.age between r.Start and r.[End] then 1 end) * 100.0 / (select count(*) from employees) 
from (
    select 18 as Start, 20 as [End]
    union all      
    select 21 as Start, 25 as [End]
    union all      
    select 26 as Start, 40 as [End]
) r  
left outer join employees e on e.age between r.Start and r.[End]
group by cast(r.Start as varchar(3)) + '-' + cast(r.[End] as varchar(3))

SQL小提琴示例#2

你通常想用windows函数做这样的事情：

Select t.range as [age interval] , Count(*) as 'number of appereances',
       cast(count(*)*100.0/tot as varchar(256))+'%' as 'percent'
from (Select (case when age between 18 and 26 then '18-26'
                  when age between 26 and 40 then '26-40'
              end) as range,
             count(*) over (partition by NULL) as tot
      from employees) t
group by t.range

我还按照示例中的格式对数字进行了格式化。

选择

SUM(CASE WHEN [dbo].[GetAge](DateOfBirth) < 20 THEN 1 ELSE 0 END) AS [Under_20],
    SUM(CASE WHEN [dbo].[GetAge](DateOfBirth) BETWEEN 20 AND 25 THEN 1 ELSE 0 END) AS [Age_21_25],
    SUM(CASE WHEN [dbo].[GetAge](DateOfBirth) >=26 THEN 1 ELSE 0 END) AS [Age_26_Elder]

from AspNetUsers(nolock) au inner join AspNetUserRoles(nolock) aur
on au.Id=aur.UserId inner join AspNetRoles(nolock) ar on aur.RoleId=ar.Id
Inner join StudentProfiles(nolock) st on au.Id = st.UserId

Select 
CAST(ROUND(count(case when 18 <= age and  age < 26 then 1 end) * 100.0 / count(*),2)AS NUMERIC(8,2)) as '18-26'
,CAST(ROUND(count(case when 26 <= age and  age < 40 then 1 end) * 100.0 / count(*),2)AS NUMERIC(8,2)) as '26-40'
From employees

加obtimesée