Calculate Actual Downtime ignoring overlap in dates/times

Question

I\'m trying to work out how to calculate actual downtime for various applications from data I\'m storing within a table.

At the moment I\'m just calculating the dif

Answer 1

I had a similar problem, and I got it answered in my question How to Consolidate Blocks of Time?

In your case, this is accomplished with a top 1 self outer apply to get the overlap, and then use either the Overlap's Start time, or if null, the normal Record's end time as the end time.

CREATE TABLE Downtime (
    Application VARCHAR(25), 
    DowntimeStart DATETIME,
    DowntimeEnd DATETIME,
    Expected INT
)

INSERT Downtime (Application, DowntimeStart, DowntimeEnd, Expected) VALUES -- Act/Exp
    ('Application Demo', '2014-11-20 17:31:01.467', '2014-11-20 18:01:01.243', 30) -- 30/30
    ,('Application Demo', '2014-11-28 17:59:00.987', '2014-11-28 18:09:02.167', 26) -- 10/26
    ,('Application Demo', '2014-11-28 18:00:01.403', '2014-11-28 18:25:01.443', 0) -- 25/0
    ,('Application Demo', '2014-11-29 19:13:08.580', '2014-11-30 05:30:01.763', 617) -- 617/617
    ,('Application Demo', '2014-11-30 01:55:01.953', '2014-11-30 03:54:01.730', 0)


SELECT
    Records.Application, Records.DowntimeStart, Records.DowntimeEnd, Records.Expected
  , DATEDIFF(minute, Records.DowntimeStart, COALESCE(Overlap.DowntimeStart, Records.DowntimeEnd)) AS Actual
--  , Overlap.Application, Overlap.DowntimeStart, Overlap.DowntimeEnd -- For Verification Purposes
FROM Downtime Records
  OUTER APPLY (
    SELECT TOP 1 Overlap.Application, Overlap.DowntimeStart, Overlap.DowntimeEnd
    FROM Downtime Overlap
    WHERE Records.Application = Overlap.Application
      AND Overlap.DowntimeStart > Records.DowntimeStart
      AND Overlap.DowntimeStart BETWEEN Records.DowntimeStart AND Records.DowntimeEnd
    ORDER BY Overlap.DowntimeStart
    ) Overlap

Here's the SQLFiddle with the solution.