How to combine two rows and calculate the time difference between two timestamp values in MySQL?

Question

I have a situation that I\'m sure is quite common and it\'s really bothering me that I can\'t figure out how to do it or what to search for to find a relevant example/soluti

Answer 1

How about this:

SELECT start_log.ts AS start_time, end_log.ts AS end_time
FROM log AS start_log
INNER JOIN log AS end_log ON (start_log.name = end_log.name AND end_log.ts > start_log.ts)
WHERE NOT EXISTS (SELECT 1 FROM log WHERE log.ts > start_log.ts AND log.ts < end_log.ts)
 AND start_log.eventtype = 'start'
 AND end_log.eventtype = 'stop'

This will find each pair of rows (aliased as start_log and end_log) with no events in between, where the first is always a start and the last is always a stop. Since we disallow intermediate events, a start that's not immediately followed by a stop will naturally be excluded.