select type , count(*) from 
(
  select * , case when datediff(year,birthday,getdate()) <= 35 then '35岁以下' 
                when datediff(year,birthday,getdate()) >= 36 and datediff(year,birthday,getdate()) <= 45 then '36-45岁'
                when datediff(year,birthday,getdate()) >= 46 and datediff(year,birthday,getdate()) <= 55 then '46-55岁'
                when datediff(year,birthday,getdate()) >= 56 and datediff(year,birthday,getdate()) <= 65 then '56-65岁'
                when datediff(year,birthday,getdate()) > 65 and  then '65岁以上'
           end type
  from tb
) t
group by type

------解决方案--------------------
SQL code

select type , count(*) from 
(
  select * , case when datediff(year,birthday,getdate()) <= 35 and datepart(month,birthday)<=datepart(month,getdate()) and datepart(day,birthday)<=datepart(day,getdate()) then '35岁以下' 
                 when datediff(year,birthday,getdate()) between 36 and 45 and datepart(month,birthday)<=datepart(month,getdate()) and datepart(day,birthday)<=datepart(day,getdate()) then '36-45岁'
                 when datediff(year,birthday,getdate()) between 46 and 55 and datepart(month,birthday)<=datepart(month,getdate()) and datepart(day,birthday)<=datepart(day,getdate()) then '46-55岁'
                 when datediff(year,birthday,getdate()) between 56 and 65 and datepart(month,birthday)<=datepart(month,getdate()) and datepart(day,birthday)<=datepart(day,getdate()) then '56-65岁'
                 when datediff(year,birthday,getdate()) > 65 and datepart(month,birthday>datepart(month,getdate()) and datepart(day,birthday)>datepart(day,getdate()) then '65岁以上'
            end type
  from tb
) t
group by type