On 03/17/2015 10:57 AM, Israel Brewster wrote:
On Mar 17, 2015, at 9:30 AM, Paul Jungwirth <pj@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
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:
Sounds reasonable. I've never worked with range values before, but it does seem appropriate here.
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
Gotcha
My take on this is using CASE.
Rough sketch:
WHEN
date_trunc('hour', end_time) < h
THEN
end_time - start_time
ELSE
(date_trunc('hour', start_time) + interval '1 hr') - start_time
as
active_time
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.
Right. And I will run into some of those (at least the crossing midnight), so I'll keep an eye out.
-----------------------------------------------
Israel Brewster
Systems Analyst II
Ravn Alaska
5245 Airport Industrial Rd
Fairbanks, AK 99709
(907) 450-7293
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Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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