IF OBJECT_ID('F_getmonths') IS NOT NULL DROP FUNCTION  F_getmonths
GO
CREATE FUNCTION F_getmonths
(@n_date datetime
)
RETURNS @tb_month table(第一天 datetime,最后一天 datetime)
AS
BEGIN
   declare @N_day int 
   declare @first_date datetime,@last_date datetime
   set @n_day=datepart(dd,@n_date)
   if @n_day >25
     begin 
         set @first_date=cast(cast(year(@n_date) as varchar)+'-'+cast(month(@n_date)as varchar)+'-26' as datetime)
         set @last_date=cast(cast(year(@n_date) as varchar)+'-'+cast(month(dateadd(mm,1,@n_date))as varchar)+'-25' as datetime)
     end
   else 
       begin
          set @first_date=cast(cast(year(@n_date) as varchar)+'-'+cast(month(dateadd(mm,-1,@n_date))as varchar)+'-26' as datetime)
          set @last_date=cast(cast(year(@n_date) as varchar)+'-'+cast(month(@n_date)as varchar)+'-25' as datetime)
  
     end
       insert @tb_month select @first_date,@last_date
       return
END
GO