SQL best way to subtract a value of the previous row in the query?

Question

I\'m trying to calculate the total lost machine time in the database. The columns in the table are MachineID aka PlantID, StartTime, EndTime.

In theory its simply sort t

Answer 1

This was the resulting query I went with :)

SELECT SUM(a.StartTime - a.LagEnd) as LostTime 
FROM (SELECT [PlantID], [StartTime], [EndTime], 
             LAG([PlantID]) OVER (ORDER BY PlantID, StartTime) LagPlantID,
             LAG([EndTime]) OVER (ORDER BY PlantID, StartTime) LagEnd 
      FROM MachineRecords) a 
WHERE a.PlantID = a.LagPlantID