一个group by例子

select 
    case 
        when (datediff(yy,csrq,getdate()) > 18) then '18岁及以上'        
        when (datediff(yy,csrq,getdate()) = 11) then '11岁'
        when (datediff(yy,csrq,getdate()) = 12) then '12岁'
        when (datediff(yy,csrq,getdate()) = 13) then '13岁'
        when (datediff(yy,csrq,getdate()) = 14) then '14岁'
        when (datediff(yy,csrq,getdate()) = 15) then '15岁'
        when (datediff(yy,csrq,getdate()) = 16) then '16岁'
        when (datediff(yy,csrq,getdate()) = 17) then '17岁'
        else '10岁及以下'
    end 'AgeStage',
    count(*) as 'Num', xbm as Sex,
    XSLBM as 'Class',MZM as 'Nationality',ZJXY as Boarder
from stu_studentinfo
where  Dept_ID 
in (select id from sys_departments where p_id 
in (select id from sys_departments where p_id in (252,258,277,279) 
and gradeclass = '初一年级'))
group by 
case 
    when (datediff(yy,csrq,getdate()) > 18) then '18岁及以上'        
    when (datediff(yy,csrq,getdate()) = 11) then '11岁'
    when (datediff(yy,csrq,getdate()) = 12) then '12岁'
    when (datediff(yy,csrq,getdate()) = 13) then '13岁'
    when (datediff(yy,csrq,getdate()) = 14) then '14岁'
    when (datediff(yy,csrq,getdate()) = 15) then '15岁'
    when (datediff(yy,csrq,getdate()) = 16) then '16岁'
    when (datediff(yy,csrq,getdate()) = 17) then '17岁'
    else '10岁及以下'
end, xbm,XSLBM,MZM,ZJXY