TSQL function to find difference between two dates taking weekends and holidays into account

Tomalak posted an excellent response to an existing SO question:

SQL DateDiff advanced usage?

It almost worked for me but I needed to compute the business hours difference between two dates, excluding weekends, even if less than a week had elapsed. My solution adds a while loop (which is probably a bit naive, open to suggestions!) and adds a check for holidays in a holiday lookup table.

Edit: I'm not looking for this to be answered in the traditional sense, just wanted to get back to it easily and open it up for critiquing for those who may come across it in the future.

ALTER FUNCTION dbo.udfDateDiffBusinessHours (
  @date1 DATETIME,
  @date2 DATETIME
) RETURNS DATETIME AS
BEGIN
  DECLARE @sat INT
  DECLARE @sun INT
  DECLARE @workday_s INT
  DECLARE @workday_e INT
  DECLARE @basedate1 DATETIME
  DECLARE @baseda开发者_如何学编程te2 DATETIME
  DECLARE @calcdate1 DATETIME
  DECLARE @calcdate2 DATETIME
  DECLARE @iteratordate DATETIME
  DECLARE @cworkdays INT
  DECLARE @coffdays INT
  DECLARE @returnval INT

  SET @workday_s = 480 -- work day start:  8 hours
  SET @workday_e = 1080 -- work day end:   18 hours

    -- calculate Saturday and Sunday dependent on SET DATEFIRST option
  SET @sat = CASE @@DATEFIRST WHEN 7 THEN 7 ELSE 7 - @@DATEFIRST END 
  SET @sun = CASE @@DATEFIRST WHEN 7 THEN 1 ELSE @sat + 1 END 

  SET @calcdate1 = @date1
  SET @calcdate2 = @date2

  -- @date1: assume next day if start was after end of workday
  SET @basedate1 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate1))
  SET @calcdate1 = CASE WHEN DATEDIFF(mi, @basedate1, @calcdate1) > @workday_e
                   THEN @basedate1 + 1
                   ELSE @calcdate1
                   END

  -- @date1: if Saturday or Sunday, make it next Monday
  SET @basedate1 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate1))
  SET @calcdate1 = CASE DATEPART(dw, @basedate1)
                   WHEN @sat THEN @basedate1 + 2
                   WHEN @sun THEN @basedate1 + 1
                   ELSE @calcdate1
                   END

  -- @date1: assume @workday_s as the minimum start time
  SET @basedate1 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate1))
  SET @calcdate1 = CASE WHEN DATEDIFF(mi, @basedate1, @calcdate1) < @workday_s 
                   THEN DATEADD(mi, @workday_s, @basedate1)
                   ELSE @calcdate1
                   END

  -- @date2: assume previous day if end was before start of workday
  SET @basedate2 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate2))
  SET @calcdate2 = CASE WHEN DATEDIFF(mi, @basedate2, @calcdate2) < @workday_s
                   THEN DATEADD(mi, @workday_e, @basedate2 - 1)
                   ELSE @calcdate2
                   END

  -- @date2: if Saturday or Sunday, make it previous Friday
  SET @basedate2 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate2))
  SET @calcdate2 = CASE DATEPART(dw, @calcdate2)
                   WHEN @sat THEN @basedate2 - 0.00001
                   WHEN @sun THEN @basedate2 - 1.00001
                   ELSE @date2
                   END

  -- @date2: assume @workday_e as the maximum end time
  SET @basedate2 = DATEADD(dd, 0, DATEDIFF(dd, 0, @calcdate2))
  SET @calcdate2 = CASE WHEN DATEDIFF(mi, @basedate2, @calcdate2) > @workday_e
                   THEN DATEADD(mi, @workday_e, @basedate2)
                   ELSE @calcdate2
                   END

  -- count full work days (subtract Saturdays, Sundays and holidays)
  SET @cworkdays = DATEDIFF(dd, @basedate1, @basedate2)
  SET @iteratordate = @basedate1
  SET @coffdays = 0

  WHILE DATEDIFF(dd, @iteratordate, @basedate2) > 0
  BEGIN
    IF DATEPART(dw, @iteratordate) = @sat OR DATEPART(dw, @iteratordate) = @sun OR EXISTS (SELECT holidaydate FROM dbo.holidays_lu (NOLOCK) WHERE holidaydate = @iteratordate)
        SET @coffdays = @coffdays + 1
    SET @iteratordate = DATEADD(dd, 1, @iteratordate)
  END
  SET @cworkdays = @cworkdays - @coffdays

  -- calculate effective duration in minutes
  SET @returnval = @cworkdays * (@workday_e - @workday_s)
                   + @workday_e - DATEDIFF(mi, @basedate1, @calcdate1) 
                   + DATEDIFF(mi, @basedate2, @calcdate2) - @workday_e

  -- return duration as an offset in minutes from date 0
  RETURN DATEADD(mi, @returnval, 0)
END

---

While searching the internet I came across this solution:

How do I count the number of business days between two dates?

It's using a work calendar table, which you can adjust as you wish for marking working days (including holidays).

Counting the business hours would be querying for:

• working days between start and end date excluding both start and end date * (working hours/day)
• + working hours on start day (if it's a working day)
• + working hours on end day (if it's a working day)

Maybe it's possible to also code the business hours into the work calendar table, but I haven't tried it yet.