Question

My problem is simple: I have a table with a series of statuses and timestamps (for the sake of curiosity, these statuses indicate alarm levels) and I would like to query this table in order to get duration between two statuses.

Seems simple, but here comes the tricky part: I can´t create look-up tables, procedures and it should be as fast as possible as this table is a little monster holding over 1 billion records (no kidding!)…

The schema is drop dead simple:

[pk] Time
Value

(actualy, there is a second pk but it is useless for this)

And below a real world example:

Timestamp          Status
2013-1-1 00:00:00    1
2013-1-1 00:00:05    2
2013-1-1 00:00:10    2
2013-1-1 00:00:15    2
2013-1-1 00:00:20    0
2013-1-1 00:00:25    1
2013-1-1 00:00:30    2
2013-1-1 00:00:35    2
2013-1-1 00:00:40    0

The output, considering only a level 2 alarm, should be as follow should report the begin of a level 2 alarm an its end (when reach 0):

StartTime          EndTime            Interval
2013-1-1 00:00:05  2013-1-1 00:00:20     15
2013-1-1 00:00:30  2013-1-1 00:00:40     10

I have been trying all sorts of inner joins, but all of them lead me to an amazing Cartesian explosion. Can you guys help me figure out a way to accomplish this?

Thanks!

Answer 1

This has to be one of the harder questions I’ve seen today – thanks! I assume you can use CTEs? If so, try something like this:

;WITH Filtered
AS
(
    SELECT ROW_NUMBER() OVER (ORDER BY dateField) RN, dateField, Status
    FROM Test    
)
SELECT F1.RN, F3.MinRN,
    F1.dateField StartDate,
    F2.dateField Enddate
FROM Filtered      F1, Filtered F2, (
SELECT F1a.RN, MIN(F3a.RN) as MinRN
FROM Filtered      F1a
   JOIN Filtered F2a ON F1a.RN = F2a.RN+1 AND F1a.Status = 2 AND F2a.Status <> 2
   JOIN Filtered F3a ON F1a.RN < F3a.RN AND F3a.Status <> 2
GROUP BY F1a.RN ) F3 
WHERE F1.RN = F3.RN AND F2.RN = F3.MinRN

And the Fiddle. I didn’t add the intervals, but I imagine you can handle that part from here.

Good luck.