To put this question into context, I'm trying to calculate "time in app" based on an event log.

Assume the following table:

user_id   event_time
2         2012-05-09 07:03:38
3         2012-05-09 07:03:42
4         2012-05-09 07:03:43
2         2012-05-09 07:03:44
2         2012-05-09 07:03:45
4         2012-05-09 07:03:52
2         2012-05-09 07:06:30

I'd like to get the difference between the highest and lowest event_time from a set of timestamps that are within 2 minutes of eachother (and grouped by user). If a timestamp is outside of a 2 minute interval from the set, it should be considered a part of another set.

Desired output:

user_id  seconds_interval
2        7     (because 07:03:45 - 07:03:38 is 7 seconds)
3        0     (because 07:03:42)
4        9     (because 07:03:52 - 2012-05-09 07:03:43)
2        0     (because 07:06:30 is outside 2 min interval of 1st user_id=2 set)

This is what I've tried, although I can't group on seconds_interval (even if I could, I'm not sure this is the right direction):

SELECT (max(tr.event_time)-min(tr.event_time)) as seconds_interval
FROM some_table tr
INNER JOIN TrackingRaw tr2 ON (tr.event_time BETWEEN 
   tr2.event_time - INTERVAL 2 MINUTE AND tr2.event_time + INTERVAL 2 MINUTE) 
GROUP BY seconds_interval