create table #t(Uname varchar(10),age int)
insert #t
select '啊啊',19 union all 
select '資訊',23 union all  
select '寶寶',31 union all  
select '喔喔',21 union all  
select '米米',6 
select nnd as '年齡段',count(*) as '人數' from(
 select 
 case
  when age>=1 and age<=10 then '1-10'
  when age>=11 and age<=20 then '11-20'
  when age>=21 and age<=30 then '21-30'
  when age>=31 and age<=40 then '31-40' 
 end 
 as nnd,uname from #t
)a group by nnd