>With that WHERE clause you filter first and last record from the example data.
>Maybe you need:
>

>WHERE (BusinessTime.Start>=@Start AND BusinessTime.Start<=@End) OR
>      (BusinessTime.[End]>=@Start AND BusinessTime.[End]<=@End)) Temp
>

Thanks, your approach is better. This would give this:

DECLARE @Start DATETIME
DECLARE @End DATETIME
 
SET @Start='2014-01-23 09:15:00'
SET @End='2014-01-29 13:45:00'
 
SELECT SUM(Temp.SecondValue)/3600 AS HourValue
FROM (SELECT CAST(DATEDIFF(SECOND,
 CASE WHEN BusinessTime.Start>@Start THEN BusinessTime.Start ELSE @Start END,
 CASE WHEN BusinessTime.[End]<@End THEN BusinessTime.[End] ELSE @End END) AS DECIMAL(10,2)) AS SecondValue
 FROM BusinessTime
 WHERE (BusinessTime.Start>=@Start AND BusinessTime.Start<=@End) OR
  (BusinessTime.[End]>=@Start AND BusinessTime.[End]<=@End)) Temp

However, this gives 35.5 not 31.5.