Using UDF in SELECT statement

Question

I made a user-define function for business hours calculation.

This is my UDF.

CREATE FUNCTION  fn_GetBusinessHour (@date datetime, @addHours int)
RETURNS datetime
AS
BEGIN 
    DECLARE @CalcuatedDate datetime;
    DECLARE @addDayCount int, @addHourCount int, @addMinCount int;

    SET @addDayCount = @addHours / 8.5;
    SET @addHourCount = @addHours - (@addDayCount * 8.5);
    SET @addMinCount =  @addHours - (@addDayCount * 8.5) - @addHourCount;

    IF(@addDayCount != 0) 
        SET @CalcuatedDate = DATEADD(DD, @addDayCount, @date); 

    SET @CalcuatedDate = DATEADD(HH, @addHourCount, @CalcuatedDate);

    IF(@addMinCount != 0) 
        SET @CalcuatedDate = DATEADD(MM, @addMinCount, @CalcuatedDate); 

    RETURN @CalcuatedDate;
END

When I test using following statement,

SELECT dbo.fn_GetBusinessHour(GETDATE(), 40)

It shows proper result.

However, I use my function like this,

SELECT TicketID
     , DateTimeLogged --Type: Datetime
     , Priority       --Type: int
     , [dbo].[fn_GetBusinessHour](DateTimeLogged, Priority)
  FROM TicketHeader

the result shows only NULL value.

TicketID    DateTimeLogged  Priority    (No column name)
1   2011-07-04 11:26:19.510     30  NULL
2   2011-07-04 13:58:45.683     30  NULL
3   2011-07-05 10:09:16.923     10  NULL
4   2011-07-05 13:13:30.237     30  NULL
5   2011-07-05 16:50:34.033     20  NULL

I tried CONVERT because it worked when I give a value 40 but it also shows null values.

SELECT TicketID
         , DateTimeLogged --Type: Datetime
         , Priority       --Type: int
         , [dbo].[fn_GetBusinessHour](DateTimeLogged, CONVERT(int, Priority))
      FROM TicketHeader

How can I fix this to work my UDF? Why this thing happen? I cannot understand what is different between Priority and 40.

Thank you in advance.

Aaron Bertrand · Accepted Answer · 2012-06-25 02:22:49Z

For values of priority > 8.5, this seems to work fine for me:

DECLARE @t TABLE(TicketID INT, DateTImeLogged DATETIME, Priority INT);

INSERT @t SELECT 1,'20110704 11:26:19.510',30
UNION ALL SELECT 2,'20110704 13:58:45.683',30
UNION ALL SELECT 3,'20110705 10:09:16.923',10
UNION ALL SELECT 4,'20110705 13:13:30.237',30
UNION ALL SELECT 5,'20110705 16:50:34.033',20;

SELECT TicketID
     , DateTimeLogged --Type: Datetime
     , Priority       --Type: int
     , [dbo].[fn_GetBusinessHour](DateTimeLogged, Priority)
  FROM @t;

Yields:

TicketID  DateTimeLogged           Priority  (No column name)
--------  -----------------------  --------  -----------------------
1         2011-07-04 11:26:19.510  30        2011-07-07 15:26:19.510
2         2011-07-04 13:58:45.683  30        2011-07-07 17:58:45.683
3         2011-07-05 10:09:16.923  10        2011-07-06 11:09:16.923
4         2011-07-05 13:13:30.237  30        2011-07-08 17:13:30.237
5         2011-07-05 16:50:34.033  20        2011-07-07 19:50:34.033

If I add another row with a Priority < 8.5, e.g.:

INSERT @t SELECT 6,'20110705 13:13:30.237',5;

Then this row is added to the result:

TicketID  DateTimeLogged           Priority  (No column name)
--------  -----------------------  --------  -----------------------
6         2011-07-05 13:13:30.237  5         NULL

In other words, the function will output NULL if the function logic leaves @CalculatedDate unassigned, which will happen if @addDayCount = 0. In the function you say:

IF(@addDayCount != 0) 
    SET @CalcuatedDate = DATEADD(DD, @addDayCount, @date);

Since @addDayCount is an INT, try this:

DECLARE @addDayCount INT;
SET @addDayCount = 5 / 8.5;
SELECT @addDayCount;

Result:

So because @CalculatedDate isn't assigned a value initially, all of the following DATEADD operations are performing DATEADD(interval, number, NULL) which still yields NULL.

So perhaps you need to use a different data type for the variables in the function...

Thank you so much @aaronb. Finally I knew it. I add one line DECLARE CalcuatedDate = date. It prevent DATEADD(interval, number, NULL). Thank you again.

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