SQL DateDiff advanced usage?

Question

I need to calculate the DateDiff (hours) between two dates, but only during business-hours (8:30 - 16:00, no weekends). This result will then be put into the Reaction_Time c

Answer 1

This function will give you the difference in business hours between two given times. This will return the difference in minutes or hours based on the date part parameter.

CREATE FUNCTION [dbo].[fnBusinessHoursDateDiff] (@StartTime SmallDatetime, @EndTime SmallDateTime, @DatePart varchar(2)) RETURNS DECIMAL (10,2)
AS 
BEGIN

DECLARE @Minutes        bigint
    ,   @FinalNumber    Decimal(10,2)

-- // Create Minute By minute table for CTE
-- ===========================================================
;WITH  cteInputHours (StartTime, EndTime, NextTime) AS (
    SELECT  @StartTime  
        ,   @EndTime    
        ,   dateadd(mi, 1, @StartTime)
 ),
 cteBusinessMinutes (TimeOfDay, [isBusHour], NextTime) AS(
    SELECT  StartTime [TimeOfDay]
        ,   case when datepart(dw, StartTime) between 2 and 6 and convert(time,StartTime) between '08:30' and '15:59' then 1 else 0 end [isBusHour]
        ,   dateadd(mi, 1, @StartTime)  [NextTime]
    FROM    cteInputHours
    UNION ALL
    SELECT  dateadd(mi, 1, (a.TimeOfDay)) [TimeOfDay]
        ,   case when datepart(dw, a.TimeOfDay) between 2 and 6 and  convert(time,dateadd(mi, 1, (a.TimeOfDay)) ) between '08:30' and '15:59' then 1 else 0 end [isBusHour]
        ,   dateadd(mi, 2, (a.TimeOfDay)) NextTime
    FROM    cteBusinessMinutes a
    WHERE   dateadd(mi, 1, (a.TimeOfDay)) < @EndTime
) 
SELECT  @Minutes = count(*)
FROM    cteBusinessMinutes
WHERE   isBusHour = 1
OPTION (MAXRECURSION 0);

-- // Final Select
-- ===========================================================
SELECT  @FinalNumber = @Minutes / (case when @DatePart = 'hh' then 60.00 else 1 end)

RETURN @FinalNumber 

END