So next question: how do I get the "active" time per hour from this?
I think you just SUM() over the intersection between each hourly window
and each event, right? This might be easiest using tsrange, something
like this:
SUM(extract(minutes from (tsrange(start_time, end_time) &&
tsrange(h, h + interval '1 hour'))::interval))
I think you'll have to implement ::interval yourself though, e.g. here:
http://dba.stackexchange.com/questions/52153/postgresql-9-2-number-of-days-in-a-tstzrange
Also as mentioned you'll have to convert h from an integer [0,23] to a
timestamp, but that seems pretty easy. Assuming start_time and end_time
are UTC that's just adding that many hours to UTC midnight of the same day.
Some weird edge cases to be careful about: activities that cross
midnight. Activities that last more than one full day, e.g. start 3/15
and end 3/17.
Paul
