Finding the Next Business Day Recursively

  • Rob Scholl

    Old Hand

    Points: 300

    Comments posted to this topic are about the content posted at http://www.sqlservercentral.com/columnists/rScholl/findingthenextbusinessdayrecursively.asp

  • Phil Paxton

    SSC Veteran

    Points: 234

    I have to quibble a bit on the definition of recursion and the article provides a hint to support this.

    "Way back when", recursion was taught as "a function which calls itself with parameters|data|whatever in a simpler version of themselves [compared to what was passed in].  Eventually, you will reach a base or termination case which will cause the recursion to unravel itself and provide a solution.

     

  • Andre Araujo-272450

    SSC Enthusiast

    Points: 157

    Rob,

      for some reason your function didn't work for me. I changed it a bit to get it working here and changed basically two things:

    1) As we are using recursion there is no need for an explicit loop inside the function. The iteration is done using the consecutive calls to the function.

    2) I get rid of the HH:MM:SS of the startDate in order to compare with the dates on the Holiday table. Otherwise the comparison would be like '2005-11-07 16:41:03' = '2005-11-07 00:00:00', which would evaluate to FALSE.

    Below is the code with the changes.

    Cheers,

    Andre

    create function fnGetNextBusinessDay (@startDate smalldatetime)

    returns smalldatetime as

    Begin

    Declare @nextBusDay smalldatetime

    Declare @weekDay tinyInt

    set @nextBusDay = convert(datetime,left(convert(varchar,@startDate + 1,120),10),120) -- first get the raw next day

    SET @weekDay =((@@dateFirst+datePart(dw,@nextBusDay)-2) % 7) + 1

    if @weekDay in (6, 7) or exists (select 1 from holiday where holidayDate = @nextBusDay)

    set @nextBusDay = dbo.fnGetNextBusinessDay(@nextBusDay)

    return (@nextBusDay)

    End

  • Hugo Kornelis

    SSC Guru

    Points: 64645

    Hi Rob,

    While the function uses some nifty tricks (I particularly like the trick to get correct results regardless of datefirst setting; this is a new trick for me), I'd never recommend using this function to anyone.

    There are other ways to achieve this. Ways that are, in my opinion, better. Check out http://www.aspfaq.com/show.asp?id=2519, and especially the section titled "Pre-determine delivery dates".

    Best, Hugo


    Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
    Visit my SQL Server blog: https://sqlserverfast.com/blog/
    SQL Server Execution Plan Reference: https://sqlserverfast.com/epr/

  • Ian Yates

    SSCoach

    Points: 19738

    Elegant solution (I too like the trick to get the correct day regardless of datefirst!  Clever!).  BUT...  recursion in SQL is limited to 32 calls (XMAS holidays in schools, for example, go a lot longer than this) - it could easily have been done with a simple loop, or better yet, a simple select statement...

    In our software where we have to keep track of days a clinic is open for business, rather than messing around with such procedures, we just have a dates table with one value for each day and a bit flag representing opened or closed...  Makes reporting VERY easy and you can join to the table easily to group days together efficiently, etc.  For similar ideas and more info on why just storing the data in a table can be efficient, look up "numbers table" on this site - Adam Machanic has quite a bit written about them.

    But I still like that modulus trick!!

  • Mark Firth-200666

    Old Hand

    Points: 333

    Cute, but I agree with Ian, if you are using a table why not maintain the correct dates in the table, it is MUCH easier to work with.

    I did not know the 32 levels of recursion limitation, thanks

  • Mark Hickin

    Say Hey Kid

    Points: 693

    One thing to note.

    @@Datefirst is affected by things like the defaultlanguage property of your language.

    I believe that for the US @@Datefirst defaults to 7, whereas if you set up your login to use British English, as we brits often do, it will be 1.

    This will affect what Datepart(weekday, getdate()) returns.

    Just something to be aware of, I've had problems with this before.

     

     

  • David Jackson

    SSCertifiable

    Points: 6404

    Paul Cresham posted an elegant solution for this including working out holidays on the fly, albeit for the UK.  It did contain a nifty Easter algorithm, as well as tackling the @@DATEFIRST problem.  see

    http://www.sqlservercentral.com/forums/shwmessage.aspx?forumid=23&messageid=110259

    I documented it with an example of how we use it at

    http://glossopian.co.uk/pmwiki.php?n=Main.WorkingDays

    Dave Jackson


    http://glossopian.co.uk/
    "I don't know what I don't know."

  • Mike C

    SSC-Insane

    Points: 23224

    Here's another version of the Easter Calculation algorithm:

    http://sqlservercentral.com/cs/blogs/michael_coles/archive/2005/07/16/49.aspx

    And something for calculating "floating" American holidays:

    http://sqlservercentral.com/cs/blogs/michael_coles/archive/2005/07/17/52.aspx

     

  • mdolan1959

    Old Hand

    Points: 369

    Rob- I like this example. It will work for our business because we don't take long holidays

    Thanks, Matt


    Matt Dolan

  • John McLaughlin-213204

    Old Hand

    Points: 310

    Here's another function that takes a simpler approach. If you are maintaining a holiday table, it would be simple enough to check the return value against it as well.

     

    John

     

    CREATE       FUNCTION dbo.udf_GetNextBizDay (@dDateValue DATETIME)

    RETURNS Datetime

    AS 

    ---------------------------------------------------------------------------------

    --

    -- Modification History:

    --

    -- Date                     Version  Programmer Comments

    -- ------------------       -------  ---------- ----------------------------

    -- 2005-06-13 02:23:00  1.0  John McLaughlin 

    --

    --

    BEGIN

     DECLARE @dReturnDate DATETIME

     

     IF ISDATE(@dDateValue)=0

      BEGIN

       RETURN NULL

      END

     

     SET @dReturnDate = DATEADD(d,1,@dDateValue)

     --Set to zero hour. Uncomment if needed.

     --SET @dReturnDate = CAST(CONVERT(CHAR(10),@dReturnDate,101) AS DATETIME)

     WHILE DATEPART(dw,@dReturnDate) in(1,7)

      BEGIN

       SET @dReturnDate = DATEADD(d,1,@dReturnDate)

      END

     

     RETURN @dReturnDate

    END

  • Jason1972

    SSC Veteran

    Points: 206

    I like the trick for handling the DATEFIRST.  With it, you can write the function in 3 lines without recursion, which I think is a bit more elegant.

    CREATE FUNCTION dbo.fnGetNextBusinessDay (@Date datetime) RETURNS datetime AS

    BEGIN

         SET @Date = DATEADD(dd, 1, CONVERT(datetime, (CONVERT(CHAR(10), @Date, 101))))

         WHILE ((@@DATEFIRST + DATEPART(dw, @Date) - 1) % 7) + 1 IN (1, 7) OR @Date IN (SELECT HolidayDate FROM Holiday) SET @Date = DATEADD(dd, 1, @Date)

         RETURN @Date

    END

     

  • Ninja's_RGR'us

    SSC Guru

    Points: 294069

    Hey Joe, don't you feel like you are talking for nothing sometimes???

     

    Guys, Joe literally wrote the book on SQL, he wrote the ISO standards for SQL.  I would strongly suggest you listen to him on this one... and basically any other post he makes .

     

    Even if it seems like overkill this time, and the next time and the time after that.  Won't you wish you had taken the time to write one when you decid to implement it the nth time... and then decid to make that the business rule to implement overall once you see the benefits??

  • TriggerMe

    SSChampion

    Points: 11752

    I don't understand the @numDays input parameter!

    For example if do this,

    DECLARE

    @Date SMALLDATETIME

    SET

    @Date = dbo.fnGetNextBusinessDay ('2006-12-24', 10)

    SELECT

    @Date

    It's suppsoe to return the date 2006-12-27 as that is the next business day.

    Can someone explain please?


    Kindest Regards,

  • Hugo Kornelis

    SSC Guru

    Points: 64645

    Hi Trigger,

    The @numDays parameter is the number of business days to move forward in time.

    To get 2006-12-27, you should have used:

    SET @Date = dbo.fnGetNextBusinessDay ('2006-12-24', 1)

    to get the "first" next business day. Your use of:

    SET @Date = dbo.fnGetNextBusinessDay ('2006-12-24', 10)

    should get the 10th next business day.


    Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
    Visit my SQL Server blog: https://sqlserverfast.com/blog/
    SQL Server Execution Plan Reference: https://sqlserverfast.com/epr/

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