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

>
>
>--
>  Adrian Klaver
>  adrian.klaver@aklaver.com
>
>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