SQL按照月份查询该月有多少条数据

在SQLServer中按照月份查询该月有多少条数据（近三个月）

DATENAME() 截取时间中的年，月，日

   select t.time,COUNT(*)as sum from 
   (select ( DATENAME(year, datetime) + '-' + DATENAME(MONTH,datetime))as time,COUNT(*)  as number From CeShi t
   where DATENAME(year, datetime) + '-' + DATENAME(MONTH, datetime)
    between  DateName(year,GetDate()) +'-'+convert(varchar,(convert(int,DateName(MONTH,GetDate())-2)))
   and DateName(year,GetDate()) +'-'+convert(varchar,(convert(int,DateName(MONTH,GetDate()))))
   group by datetime) t
   group by t.time