Simple subtraction in a table

[Anon]

I have a web site that tracks helicopters. I capture the "from_location" "to_location", "off_time"and "on_time". It's know problem to calculate the flight time. I need a sql that will grab the next row "on_time" and subtract it from the current row "off_time", this will give me the helicopter standby time. Can anyone help?

Paul

[[deleted]]

You will have to do this for every flight.

What you are looking for is the smallest (most recent) on-time that is still later than the current off-time, and where the helicopter_id is the same.

something like:
SELECT min(on_time)
FROM table
WHERE helicopter_id = $your_heli_id
AND on_time> $the_off_time_from_last_flight