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

UPDATED WITH NEW TEST CASES

Here is one technique that calculates the unique outages and then aligns them back to the initial downtime causing the outage so that the actual and expected values match.

DECLARE @Downtime TABLE (
    ID INT PRIMARY KEY NOT NULL IDENTITY(1,1),
    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)
    ,('Application Demo 2', '2014-12-19 23:09:01.303', '2014-12-22 09:43:01.397', 3514)
    ,('Application Demo 2', '2014-12-19 23:09:01.303', '2014-12-22 09:43:01.397', 0)
    ,('Application Demo 2', '2014-12-19 23:09:01.303', '2014-12-22 09:43:01.397', 0) 
    ,('Application Demo 2', '2014-12-19 23:09:01.303', '2014-12-22 09:43:01.397', 0)
    ,('Application Demo 2', '2014-12-19 23:09:01.303', '2014-12-22 09:43:01.397', 0) 

SELECT
    Downtimes.Application,
    Downtimes.DowntimeStart,
    Downtimes.DowntimeEnd,
    Downtimes.Expected,
    COALESCE(Actual, 0) AS Actual
FROM @Downtime Downtimes
    LEFT OUTER JOIN (
        SELECT DISTINCT
            D1.Application,
            MIN(CASE WHEN D1.DowntimeStart < D2.DowntimeStart THEN D1.ID ELSE D2.ID END) AS [ID],
            MIN(CASE WHEN D1.DowntimeStart < D2.DowntimeStart THEN D1.DowntimeStart ELSE D2.DowntimeStart END) AS [DowntimeStart],
            MAX(CASE WHEN D1.DowntimeEnd > D2.DowntimeEnd THEN D1.DowntimeEnd ELSE D2.DowntimeEnd END) AS [DowntimeEnd],
            DATEDIFF(MINUTE,
                MIN(CASE WHEN D1.DowntimeStart < D2.DowntimeStart THEN D1.DowntimeStart ELSE D2.DowntimeStart END),
                MAX(CASE WHEN D1.DowntimeEnd > D2.DowntimeEnd THEN D1.DowntimeEnd ELSE D2.DowntimeEnd END)) AS Actual
        FROM @Downtime D1
            INNER JOIN @Downtime D2
                ON D1.Application = D2.Application
                    AND (D1.DowntimeStart BETWEEN D2.DowntimeStart AND D2.DowntimeEnd
                        OR D2.DowntimeStart BETWEEN D1.DowntimeStart AND D1.DowntimeEnd)
        GROUP BY
            D1.Application,
            D1.DowntimeStart
    ) Outages
        ON Outages.ID = Downtimes.ID

And this yields the desired output:

Application               DowntimeStart           DowntimeEnd             Expected    Actual
------------------------- ----------------------- ----------------------- ----------- -----------
Application Demo          2014-11-20 17:31:01.467 2014-11-20 18:01:01.243 30          30
Application Demo          2014-11-28 17:59:00.987 2014-11-28 18:09:02.167 26          26
Application Demo          2014-11-28 18:00:01.403 2014-11-28 18:25:01.443 0           0
Application Demo          2014-11-29 19:13:08.580 2014-11-30 05:30:01.763 617         617
Application Demo          2014-11-30 01:55:01.953 2014-11-30 03:54:01.730 0           0
Application Demo 2        2014-12-19 23:09:01.303 2014-12-22 09:43:01.397 3514        3514
Application Demo 2        2014-12-19 23:09:01.303 2014-12-22 09:43:01.397 0           0
Application Demo 2        2014-12-19 23:09:01.303 2014-12-22 09:43:01.397 0           0
Application Demo 2        2014-12-19 23:09:01.303 2014-12-22 09:43:01.397 0           0
Application Demo 2        2014-12-19 23:09:01.303 2014-12-22 09:43:01.397 0           0