subtracting 2 datetime values

[tomcbr]

I need to subtract 2 datetime values.

The values are from the same view table but 2 different rows.

The points in the table are Alarm points which are generated via an after hours push button for air conditioning. The first point is the time the alarm is first initiated and the second is the time the alarm is disabled after the after hours timer disables.

Below are the queries which I am using to retrieves each value presently.

SELECT LastAlarmDetailsByTime.originalAlarmTime
FROM         LastAlarmDetailsByTime
WHERE      (lan = 20) AND (os = 41) AND (theModule = N'i1') AND (AlarmCode = N'DI=1')
ORDER BY originalAlarmTime DESC

SELECT LastAlarmDetailsByTime.originalAlarmTime
FROM         LastAlarmDetailsByTime
WHERE      (lan = 20) AND (os = 41) AND (theModule = N'i1') AND (AlarmCode = N'CDI1')
ORDER BY originalAlarmTime DESC

[ck9663]

What is the column that link this two? Equipment ID perhaps? And your query is almost identical, too. Do you just need the value from the previous row after sorting by date?


~~ CK

[tomcbr]

I am a little unsure what you mean by “column that links the two”
Basically I need to subtract the first query’s "originalAlarmTime" from the second query’s "originalAlarmTime".

Sorry for my ignorance, I am very new to this as I am an electrician working with building management systems.