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MS SQL Measure Duration Between Selected Rows Using A Date & Time Field

Elisys asked
Last Modified: 2015-01-13
Dear Experts,

I have a SQL table which holds alarm history data stored chronologically. There is a DateTime field entered into teach record together with the alarm label and alarm state depicting whether the alarm was ON or OFF when the record was stored.

I would like to generate a query to measure the length of time each alarm was ON over a customisable period. The result list should show this for each individual alarm recorded during the selected period.

The query which shows everything is as follows.

SELECT App_DateTime, Label, Priority, Enum_Status, Cycle FROM History

App_DateTime = date and time when record was entered into History.
Label = a unique text identifier for each alarm.
Priority = intiger depicting the priority of the alarm 0 to 4.
Enum_Status = the status of the alarm 1 = ON and 0 = OFF.
Cycle = the number of times the alarm has gone ON/OFF.

 The Label filed is unique to each alarm. Attached is a typical list of historical alarms where orange is ON and white is OFF. I need to produce a list showing the total ON time for each alarm in the period.
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