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

DECLARE @BusHourStart DATETIME, @BusHourEnd DATETIME
SELECT @BusHourStart = '08:30:00', @BusHourEnd = '16:00:00'
DECLARE @BusMinutesStart INT, @BusMinutesEnd INT
SELECT @BusMinutesStart = DATEPART(minute,@BusHourStart)+DATEPART(hour,@BusHourStart)*60, 
@BusMinutesEnd = DATEPART(minute,@BusHourEnd)+DATEPART(hour,@BusHourEnd)*60 
DECLARE @Dates2 TABLE (ID INT, DateStart DATETIME, DateEnd DATETIME)
INSERT INTO @Dates2
SELECT 1, '15:00:00 04/29/2003', '11:00:00 04/30/2003' UNION
SELECT 2, '14:00:00 04/30/2003', '14:00:00 05/01/2003' UNION
SELECT 3, '14:00:00 05/02/2003', '14:00:00 05/06/2003' UNION
SELECT 4, '14:00:00 05/02/2003', '14:00:00 05/04/2003' UNION
SELECT 5, '07:00:00 05/02/2003', '14:00:00 05/02/2003' UNION
SELECT 6, '14:00:00 05/02/2003', '23:00:00 05/02/2003' UNION
SELECT 7, '07:00:00 05/02/2003', '08:00:00 05/02/2003' UNION
SELECT 8, '22:00:00 05/02/2003', '23:00:00 05/03/2003' UNION
SELECT 9, '08:00:00 05/03/2003', '23:00:00 05/04/2003' UNION
SELECT 10, '07:00:00 05/02/2003', '23:00:00 05/02/2003' 

-- SET DATEFIRST to U.S. English default value of 7.
SET DATEFIRST 7

SELECT ID, DateStart, DateEnd, CONVERT(VARCHAR, Minutes/60) +':'+ CONVERT(VARCHAR, Minutes % 60) AS ReactionTime
FROM ( 
    SELECT ID, DateStart, DateEnd, Overtime,
        CASE 
            WHEN DayDiff = 0 THEN 
                CASE 
                    WHEN (MinutesEnd - MinutesStart - Overtime) > 0 THEN (MinutesEnd - MinutesStart - Overtime) 
                    ELSE 0 
                    END
            WHEN DayDiff > 0  THEN 
                CASE 
                    WHEN (StartPart + EndPart - Overtime) > 0 THEN (StartPart + EndPart - Overtime) 
                    ELSE 0 
                    END + DayPart
            ELSE 0
        END AS Minutes 
    FROM(
        SELECT ID, DateStart, DateEnd, DayDiff, MinutesStart, MinutesEnd,
                CASE WHEN(@BusMinutesStart - MinutesStart) > 0 THEN (@BusMinutesStart - MinutesStart) ELSE 0 END +
                CASE WHEN(MinutesEnd - @BusMinutesEnd) > 0 THEN (MinutesEnd - @BusMinutesEnd) ELSE 0 END AS Overtime, 
                CASE WHEN(@BusMinutesEnd - MinutesStart) > 0 THEN (@BusMinutesEnd - MinutesStart) ELSE 0 END AS StartPart,
                CASE WHEN(MinutesEnd - @BusMinutesStart) > 0 THEN (MinutesEnd - @BusMinutesStart) ELSE 0 END AS EndPart,
                CASE WHEN DayDiff > 1 THEN (@BusMinutesEnd - @BusMinutesStart)*(DayDiff - 1) ELSE 0 END AS DayPart
        FROM (
                SELECT DATEDIFF(d,DateStart, DateEnd) AS DayDiff, ID, DateStart, DateEnd,  
                DATEPART(minute,DateStart)+DATEPART(hour,DateStart)*60 AS MinutesStart,
                DATEPART(minute,DateEnd)+DATEPART(hour,DateEnd)*60 AS MinutesEnd 
                FROM (
                        SELECT ID,
                                CASE 
                                        WHEN DATEPART(dw, DateStart) = 7 
                                        THEN DATEADD(SECOND, 1, DATEADD(DAY, DATEDIFF(DAY, 0, DateStart), 2))
                                        WHEN DATEPART(dw, DateStart) = 1 
                                        THEN DATEADD(SECOND, 1, DATEADD(DAY, DATEDIFF(DAY, 0, DateStart), 1))
                                ELSE DateStart END AS DateStart,
                                CASE 
                                        WHEN DATEPART(dw, DateEnd) = 7 
                                        THEN DATEADD(SECOND, -1, DATEADD(DAY, DATEDIFF(DAY, 0, DateEnd), 0))
                                        WHEN DATEPART(dw, DateEnd) = 1 
                                        THEN DATEADD(SECOND, -1, DATEADD(DAY, DATEDIFF(DAY, 0, DateEnd), -1))
                                ELSE DateEnd END AS DateEnd FROM @Dates2
                )Weekends
        )InMinutes
    )Overtime
)Calculation