Извличане на състоянието на сигнала през определен период от време

Опростени типове.

DECLARE @t TABLE (AlarmId INT NOT NULL, State BIT NOT NULL, TIME SMALLDATETIME NOT NULL)

INSERT @t
VALUES
(1  ,0,'2011-11-15 09:00')
,(1  ,1,'2011-12-20 13:30')
,(2  ,1,'2011-11-17 15:01')
,(2  ,0,'2011-12-15 06:57')
,(3  ,0,'2011-11-10 11:42')
,(3  ,1,'2011-12-02 13:12')
,(3  ,0,'2011-12-24 14:41')
,(4  ,1,'2011-10-09 13:25')
,(4  ,0,'2012-01-07 08:29')
,(5  ,0,'2011-11-19 07:12')
,(5  ,1,'2011-11-28 15:48')
,(6  ,0,'2011-12-14 17:29')
,(6  ,1,'2011-12-23 23:46')


DECLARE @Start DATETIME = '20111201'

--Initial State DISABLED
;WITH Disabled(AlarmId, Time) AS
(
    SELECT 
        AlarmId,
        Time
    FROM
    (
        SELECT 
            ROW_NUMBER() OVER (PARTITION BY AlarmId ORDER BY Time DESC) Ordinal,
            AlarmId,
            Time,
            State
        FROM @t
        WHERE 
            Time < @Start
    ) t
    WHERE 
        t.Ordinal = 1
    AND t.STate = 0
    UNION
    SELECT
        AlarmId,
        TIME
    FROM @t
    WHERE 
        Time >= @start AND Time < DATEADD(m,1,@STart)
    AND STate = 0

),
Enabled(AlarmId, Time) AS
(
    SELECT 
        AlarmId,
        TIME
    FROM @t
    WHERE 
        Time >= @start AND Time < DATEADD(m,1,@STart)
    AND STate = 1
),
Alarms(AlarmId) AS
(
    SELECT DISTINCT AlarmId FROM @t
)

SELECT 
    Alarms.AlarmId,
    CASE WHEN Disabled.Time >= @start AND Disabled.Time < DATEADD(m,1,@STart) THEN Disabled.Time ELSE NULL END Disabled,
    CASE WHEN Enabled.Time < Disabled.Time THEN NULL ELSE Enabled.Time END Enabled
FROM Alarms 
LEFT JOIN Enabled
    ON Alarms.AlarmId = Enabled.AlarmId
LEFT JOIN Disabled
    ON Alarms.AlarmId = Disabled.AlarmId
WHERE COALESCE(Enabled.Time, Disabled.Time) IS NOT NULL