根据年、月获取当前的天数

ALTER   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