Re: Group by range in hour of day - Mailing list pgsql-general

>>On Tue, Mar 17, 2015, at 11:30 AM, Adrian Klaver wrote:
>>> On 03/17/2015 10:57 AM, Israel Brewster wrote:
>>> >
>>> >
>>> >> On Mar 17, 2015, at 9:30 AM, Paul Jungwirth <pj@illuminatedcomputing.com> 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
easiestusing 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
>>
>>
>>Aah, should be
>>
>>WHEN
>>      date_trunc('hour', end_time) < h + 1
>> THEN
>>      end_time - start_time
>> ELSE
>>      (date_trunc('hour', start_time) + interval '1 hr') - start_time
>> as
>>     active_time
>
>Here another approach while building an hourly serie for each start/end pair, truncated to the hours:
>
>create temp table t (s timestamptz, e timestamptz);
>
>insert into t select '2015-03-16 08:15:00','2015-03-16 09:35:00';
>insert into t select '2015-03-16 09:15:00','2015-03-16 11:05:00';
>insert into t select '2015-03-16 08:00:00','2015-03-16 11:45:00';
>insert into t select '2015-03-17 15:15:00','2015-03-18 11:45:00';
>insert into t select '2015-03-17 20:15:00','2015-03-18 11:45:00';
>insert into t select '2015-03-17 21:15:00','2015-03-18 10:10:00';
>insert into t select '2015-03-18 23:30:00','2015-03-19 01:30:00';
>
>SELECT ser, SUM(
>  case when e - ser < interval '1 hour' then e-ser --end interval
>  when s >= ser then interval '1 hour' - (s - ser) --start interval
>  else interval '1 hour'
>  end ) as time_tot
>FROM
>  (select e,s,
>        generate_series(date_trunc('hour',s), date_trunc('hour',e), '1 hour') ser
>  from t
>  )foo
>group by ser
>order by 1
>
>regards,
>Marc Mamin

I missed the case when the start and end points are in the same hour:

SELECT ser, SUM(
  case when e - ser < interval '1 hour' then e - greatest(ser,s) --end interval or s&e in same hour
  when s >= ser then interval '1 hour' - (s - ser) --start interval
  else interval '1 hour'
  end ) as time_tot
FROM
  (select e,s,
        generate_series(date_trunc('hour',s), date_trunc('hour',e), '1 hour') ser
  from t
  )foo
group by ser
order by 1

Marc