create  FUNCTION f_GetRentalMonths_double(@StartDate DATETIME ,@EndDate DATE)  RETURNS DECIMAL(10,4)    AS  BEGIN    DECLARE @DiffMonths  DECIMAL(10,4) ,           @DiffDays INT ,          @BuZuMonths  DECIMAL (10,4)  SET @DiffMonths=CAST(0 AS DECIMAL(10,4))  while(@EndDate>=DATEADD(DAY,-1,DATEADD(MONTH,1,@StartDate)))  begin  SET @DiffMonths=@DiffMonths+CAST(1 AS DECIMAL(10,4))  SeT @StartDate=DATEADD(MONTH,1,@StartDate)  end  --不足月天数  SET @DiffDays = DATEDIFF(DAY,@StartDate,@EndDate) + 1 --不足月天数/月天数，得到月份数  SET @BuZuMonths=round( CAST(@DiffDays AS DECIMAL(10,2))/(CAST(365 AS DECIMAL(10,2))/CASt(12 AS DECIMAL(10,2))),4)  SET @DiffMonths=@DiffMonths+@BuZuMonths      RETURN   @DiffMonths END  GO