CREATE FUNCTION [dbo].[GetMonthDays](@YY CHAR(4), @MM CHAR(8))

RETURNS INT

AS

BEGIN

  DECLARE @Riqi DATETIME,@I INT

  if @MM<12

  begin

    SET @MM=CONVERT(CHAR(5),CONVERT(INT,@MM)+1)

  SET @Riqi = dateadd(day,-1,CONVERT(DATETIME,@YY+'-'+@MM+'-01'))

 SET @I =CAST(datepart(day,@Riqi) AS INT)

  end

  else

 SET @I =31

  return @I

END