SQL to find overlapping time periods and sub-faults - sql

Question

Long time stalker, first time poster (and SQL beginner). My question is similar to this one SQL to find time elapsed from multiple overlapping intervals, except I'm able to use CTE, UDFs etc and am looking for more detail.
On a piece of large scale equipment I have a record of all faults that arise. Faults can arise on different sub-components of the system, some may take it offline completely (complete outage = yes), while others do not (complete outage = no). Faults can overlap in time, and may not have end times if the fault has not yet been repaired.
Outage_ID StartDateTime EndDateTime CompleteOutage
1 07:00 3-Jul-13 08:55 3-Jul13 Yes
2 08:30 3-Jul-13 10:00 4-Jul13 No
3 12:00 4-Jul-13 No
4 12:30 4-Jul13 12:35 4-Jul-13 No
1 |---------|
2 |---------|
3 |--------------------------------------------------------------
4 |---|
I need to be able to work out for a user defined time period, how long the total system is fully functional (no faults), how long its degraded (one or more non-complete outages) and how long inoperable (one or more complete outages). I also need to be able to work out for any given time period which faults were on the system. I was thinking of creating a "Stage Change" table anytime a fault is opened or closed, but I am stuck on the best way to do this - any help on this or better solutions would be appreciated!

Answer 1

This isn't a complete solution (I leave that as an exercise :)) but should illustrate the basic technique. The trick is to create a state table (as you say). If you record a 1 for a "start" event and a -1 for an "end" event then a running total in event date/time order gives you the current state at that particular event date/time. The SQL below is T-SQL but should be easily adaptable to whatever database server you're using.
Using your data for partial outage as an example:
DECLARE #Faults TABLE (
StartDateTime DATETIME NOT NULL,
EndDateTime DATETIME NULL
)
INSERT INTO #Faults (StartDateTime, EndDateTime)
SELECT '2013-07-03 08:30', '2013-07-04 10:00'
UNION ALL SELECT '2013-07-04 12:00', NULL
UNION ALL SELECT '2013-07-04 12:30', '2013-07-04 12:35'
-- "Unpivot" the events and assign 1 to a start and -1 to an end
;WITH FaultEvents AS (
SELECT *, Ord = ROW_NUMBER() OVER(ORDER BY EventDateTime)
FROM (
SELECT EventDateTime = StartDateTime, Evt = 1
FROM #Faults
UNION ALL SELECT EndDateTime, Evt = -1
FROM #Faults
WHERE EndDateTime IS NOT NULL
) X
)
-- Running total of Evt gives the current state at each date/time point
, FaultEventStates AS (
SELECT A.Ord, A.EventDateTime, A.Evt, [State] = (SELECT SUM(B.Evt) FROM FaultEvents B WHERE B.Ord <= A.Ord)
FROM FaultEvents A
)
SELECT StartDateTime = S.EventDateTime, EndDateTime = F.EventDateTime
FROM FaultEventStates S
OUTER APPLY (
-- Find the nearest transition to the no-fault state
SELECT TOP 1 *
FROM FaultEventStates B
WHERE B.[State] = 0
AND B.Ord > S.Ord
ORDER BY B.Ord
) F
-- Restrict to start events transitioning from the no-fault state
WHERE S.Evt = 1 AND S.[State] = 1
If you are using SQL Server 2012 then you have the option to calculate the running total using a windowing function.

Answer 2

The below is a rough guide to getting this working. It will compare against an interval table of dates and an interval table of 15 mins. It will then sum the outage events (1 event per interval), but not sum a partial outage if there is a full outage.
You could use a more granular time interval if you needed, I choose 15 mins for speed of coding.
I already had a date interval table set up "CAL.t_Calendar" so you would need to create one of your own to run this code.
Please note, this does not represent actual code you should use. It is only intended as a demonstration and to point you in a possible direction...
EDIT I've just realised I have't accounted for the null end dates. The code will need amending to check for NULL endDates and use #EndDate or GETDATE() if #EndDate is in the future
--drop table ##Events
CREATE TABLE #Events (OUTAGE_ID INT IDENTITY(1,1) PRIMARY KEY
,StartDateTime datetime
,EndDateTime datetime
, completeOutage bit)
INSERT INTO #Events VALUES ('2013-07-03 07:00','2013-07-03 08:55',1),('2013-07-03 08:30','2013-07-04 10:00',0)
,('2013-07-04 12:00',NULL,0),('2013-07-04 12:30','2013-07-04 12:35',0)
--drop table #FiveMins
CREATE TABLE #FiveMins (ID int IDENTITY(1,1) PRIMARY KEY, TimeInterval Time)
DECLARE #Time INT = 0
WHILE #Time <= 1410 --number of 15 min intervals in day * 15
BEGIN
INSERT INTO #FiveMins SELECT DATEADD(MINUTE , #Time, '00:00')
SET #Time = #Time + 15
END
SELECT * from #FiveMins
DECLARE #StartDate DATETIME = '2013-07-03'
DECLARE #EndDate DATETIME = '2013-07-04 23:59:59.999'
SELECT SUM(FullOutage) * 15 as MinutesFullOutage
,SUM(PartialOutage) * 15 as MinutesPartialOutage
,SUM(NoOutage) * 15 as MinutesNoOutage
FROM
(
SELECT DateAnc.EventDateTime
, CASE WHEN COUNT(OU.OUTAGE_ID) > 0 THEN 1 ELSE 0 END AS FullOutage
, CASE WHEN COUNT(OU.OUTAGE_ID) = 0 AND COUNT(pOU.OUTAGE_ID) > 0 THEN 1 ELSE 0 END AS PartialOutage
, CASE WHEN COUNT(OU.OUTAGE_ID) > 0 OR COUNT(pOU.OUTAGE_ID) > 0 THEN 0 ELSE 1 END AS NoOutage
FROM
(
SELECT CAL.calDate + MI.TimeInterval AS EventDateTime
FROM CAL.t_Calendar CAL
CROSS JOIN #FiveMins MI
WHERE CAL.calDate BETWEEN #StartDate AND #EndDate
) DateAnc
LEFT JOIN #Events OU
ON DateAnc.EventDateTime BETWEEN OU.StartDateTime AND OU.EndDateTime
AND OU.completeOutage = 1
LEFT JOIN #Events pOU
ON DateAnc.EventDateTime BETWEEN pOU.StartDateTime AND pOU.EndDateTime
AND pOU.completeOutage = 0
GROUP BY DateAnc.EventDateTime
) AllOutages