Re: array_agg() with join question

Thank you. I was trying to do the order by at the sub-query level.

Thanks again.

Woody

iGLASS Networks
www.iglass.net

On Tue, May 14, 2013 at 11:37 AM, Igor Neyman <ineyman(dot)at(dot)work(at)gmail(dot)com>wrote:

>
>
>
> On Tue, May 14, 2013 at 10:08 AM, George Woodring <
> george(dot)woodring(at)iglass(dot)net> wrote:
>
>> To summarize my question at the top, why is it that when I did the JOIN,
>> the array_agg results reversed order?
>>
>> I had a function that ran the following query:
>>
>> SELECT timeslot, pollgrpid, array_agg(outval)
>> FROM
>> (SELECT * FROM rrd.a_current WHERE pollgrpid=8 ORDER BY timeslot,
>> dsnum) AS foo
>> WHERE timeslot >= now() - '1 hour'::interval AND timeslot <= now() +
>> '1 hour'::interval
>> GROUP BY timeslot, pollgrpid
>> ORDER BY timeslot;
>>
>> timeslot | pollgrpid | array_agg
>> ------------------------+-----------+----------------------------
>> 2013-05-14 08:58:00-04 | 8 | {1,1,0.00125217437744141}
>> 2013-05-14 09:00:00-04 | 8 | {1,1,0.000999927520751953}
>> 2013-05-14 09:02:00-04 | 8 | {1,1,0.00318312644958496}
>> 2013-05-14 09:04:00-04 | 8 | {1,1,0.000761985778808594}
>> 2013-05-14 09:06:00-04 | 8 | {1,1,0.000777959823608398}
>> 2013-05-14 09:08:00-04 | 8 | {1,1,0.101096868515015}
>> 2013-05-14 09:10:00-04 | 8 | {1,1,0.86168384552002}
>> 2013-05-14 09:12:00-04 | 8 | {1,1,0.00656795501708984}
>> 2013-05-14 09:14:00-04 | 8 | {1,1,0.102259159088135}
>> 2013-05-14 09:16:00-04 | 8 | {1,1,0.000636100769042969}
>>
>> I wanted to include missing timestamps in my results, so I joined it with
>> generate_series.
>>
>> SELECT timeslot, pollgrpid, array_agg(outval)
>> FROM
>> ( SELECT generate_series(rrd_timeslot('avail', now() - '58
>> minutes'::interval), now() + '1 hour'::interval, '2 minutes') AS timeslot )
>> AS bar
>> LEFT JOIN
>> (SELECT * FROM rrd.a_current WHERE pollgrpid=8 AND timeslot >=
>> now() - '1 hour'::interval AND timeslot <= now() + '1 hour'::interval ORDER
>> BY timeslot, dsnum) AS foo
>> USING(timeslot)
>> GROUP BY timeslot, pollgrpid
>> ORDER BY timeslot;
>>
>> timeslot | pollgrpid | array_agg
>> ------------------------+-----------+----------------------------
>> 2013-05-14 09:02:00-04 | 8 | {0.00318312644958496,1,1}
>> 2013-05-14 09:04:00-04 | 8 | {0.000761985778808594,1,1}
>> 2013-05-14 09:06:00-04 | 8 | {0.000777959823608398,1,1}
>> 2013-05-14 09:08:00-04 | 8 | {0.101096868515015,1,1}
>> 2013-05-14 09:10:00-04 | 8 | {0.86168384552002,1,1}
>> 2013-05-14 09:12:00-04 | 8 | {0.00656795501708984,1,1}
>> 2013-05-14 09:14:00-04 | 8 | {0.102259159088135,1,1}
>> 2013-05-14 09:16:00-04 | 8 | {0.000636100769042969,1,1}
>> 2013-05-14 09:18:00-04 | 8 | {0.000638008117675781,1,1}
>> 2013-05-14 09:20:00-04 | 8 | {0.174574136734009,1,1}
>> 2013-05-14 09:22:00-04 | 8 | {0.1006920337677,1,1}
>> 2013-05-14 09:24:00-04 | 8 | {0.00069117546081543,1,1}
>> 2013-05-14 09:26:00-04 | 8 | {0.114289045333862,1,1}
>> 2013-05-14 09:28:00-04 | 8 | {0.116230010986328,1,1}
>> 2013-05-14 09:30:00-04 | 8 | {0.0349528789520264,1,1}
>>
>> The array_agg results are reversed. I had to ODER BY timeslot, dsnum
>> desc on the right of the join to make it match. I am curious as to why this
>> happened. I am running 9.2.4.
>>
>> Thanks,
>> Woody
>>
>> iGLASS Networks
>> www.iglass.net
>>
>
> As always (with databases) order is not guaranteed unless you specify
> "ORDER BY ...".
> So, specify whatever order you want inside aggregate function:
>
> array_agg(outval order by column1)
>
> Check the docs:
>
> http://www.postgresql.org/docs/9.2/static/sql-expressions.html#SYNTAX-AGGREGATES
>
> Igor Neyman
>