在SQL中跨多行汇总日期？

Question

We have a Table that stores alarms for certain SetPoints in our system. I'm attempting to write a query that first gets the difference between two dates (spread across two rows), and then sums all of the date differences to get a total sum for the amount of time the setpoint was in alarm.

We have one database where I've accomplished similar, but in that case, both the startTime and endTime were in the same row. In this case, this is not adequate

Some example Data

|   Row   |   TagID   |   SetPointID   |         EventLogTime         |   InAlarm   |
-------------------------------------------------------------------------------------
|    1    |     1     |        2       |    2016-01-01 01:49:18.070   |      1      |
|    2    |     1     |        1       |    2016-01-01 03:23:39.970   |      1      |
|    3    |     1     |        2       |    2016-01-01 03:23:40.070   |      0      |
|    4    |     1     |        1       |    2016-01-01 08:04:01.260   |      0      |
|    5    |     1     |        2       |    2016-01-01 08:04:01.370   |      1      |
|    6    |     1     |        1       |    2016-01-01 11:40:36.367   |      1      |
|    7    |     1     |        2       |    2016-01-01 11:40:36.503   |      0      |
|    8    |     1     |        1       |    2016-01-01 13:00:30.263   |      0      |

Results

|   TagID    |   SetPointID   |   TotalTimeInAlarm   |
------------------------------------------------------
|     1      |        1       |    6.004443  (hours) |
|     1      |        2       |    5.182499  (hours) |

Essentially, what I need to do is to get the start time and end time for each tag and each setpoint, then I need to get the total time in alarm. I'm thing CTEs might be able to help, but I'm not sure.

I believe the pseudo query logic would be similar to

Define @startTime DATETIME, @endTime DATETIME

SELECT TagID,
       SetPointID,
       ABS(First Occurrence of InAlarm = True (since last occurrence WHERE InAlarm = False) 
           - First Occurrence of InAlarm = False (since last occurrence WHERE InAlarm = True)) 
       -- IF no InAlarm = False use @endTime.
GROUP BY TagID, SetPointID

Answer 1

You can use the LEAD windowed function (or LAG ) to do this pretty easily. This assumes that the rows always come in pairs with 1-0-1-0 for "InAlarm". If that doesn't happen then it's going to throw things off. You would need to have business rules for these situations in any event.

;WITH CTE_Timespans AS
(
    SELECT
        TagID,
        SetPointID,
        InAlarm,
        EventLogTime,
        LEAD(EventLogTime, 1) OVER (PARTITION BY TagID, SetPointID ORDER BY EventLogTime) AS EndingEventLogTime
    FROM
        My_Table
)
SELECT
    TagID,
    SetPointID,
    SUM(DATEDIFF(SS, EventLogTime, EndingEventLogTime))/3600.0 AS TotalTime
FROM
    CTE_Timespans
WHERE
    InAlarm = 1
GROUP BY
    TagID,
    SetPointID

Answer 2

One easy way is to use OUTER APPLY to get the next date that is not InAlarm

SELECT  mt.TagID,
        mt.SetPointID,
        SUM(DATEDIFF(ss,mt.EventLogTime,oa.EventLogTime)) / 3600.0 AS [TotalTimeInAlarm]
FROM    MyTable mt
        OUTER APPLY (SELECT MIN([EventLogTime]) EventLogTime
                     FROM   MyTable mt2
                     WHERE  mt.TagID = mt2.TagID
                            AND mt.SetPointID = mt2.SetPointID
                            AND mt2.EventLogTime > mt.EventLogTime
                            AND InAlarm = 0
                    ) oa
WHERE   mt.InAlarm = 1
GROUP BY mt.TagID,
        mt.SetPointID

LEAD() might perform better if using MSSQL 2012+

Answer 3

In SQL Server 2014+:

SELECT  tagId, setPointId, SUM(DATEDIFF(second, pt, eventLogTime)) / 3600. AS diff
FROM    (
        SELECT  *,
                LAG(inAlarm) OVER (PARTITION BY tagId, setPointId ORDER BY eventLogTime, row) ppa,
                LAG(eventLogTime) OVER (PARTITION BY tagId, setPointId ORDER BY eventLogTime, row) pt
        FROM    (
                SELECT  LAG(inAlarm) OVER (PARTITION BY tagId, setPointId ORDER BY eventLogTime, row) pa,
                        *
                FROM    mytable
                ) q
        WHERE   EXISTS
                (
                SELECT  pa
                EXCEPT
                SELECT  inAlarm
                )
        ) q
WHERE   ppa = 0
        AND inAlarm = 1
GROUP BY
        tagId, setPointId

This will filter out consecutive events with same alarm state