Re: concatenating hstores in a group by?

Thanks for the replies, appreciated...

My current solution is:

select trip_code,
station_no,
timer_sec + interval '12 hour' as NZST,
timer_sec as utc,
hstore_to_json(string_agg(values_sec::text, ', ')::hstore) as values_sec
from (select '$TRIP' as trip_code,
$STATION as station_no,
date_trunc('second', timer) as timer_sec,
values_sec
from t_reading_hstore_sec
where timer >= '$ISO_S'::timestamp - interval '12 hour'
and timer <= '$ISO_F'::timestamp - interval '12 hour') as foo
group by timer_sec, trip_code, station_no;

Convert the hstore to text, aggregate the text with string_agg(), convert back to hstore (which seems to remove duplicate keys, OK for my purpose)
and group by timer truncated to whole seconds. I also provide UTC & local timezone times for each set of readings. It is run in a bash script which passes the trip & station values to the query, as well as the start/finish times as ISO format strings.

The output is going to a Sqlite3 (Spatialite) database, which does not have hstore, or all the hstore functionality that Postgres has, but does have a json datatype which is adequate for our purposes, hence the hstore_to_json in the query.

Thanks again,

Brent Wood

Principal Technician, Fisheries
NIWA
DDI: +64 (4) 3860529
________________________________
From: David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
Sent: Monday, January 20, 2025 04:28
To: Brent Wood <Brent(dot)Wood(at)niwa(dot)co(dot)nz>
Cc: pgsql-general(at)lists(dot)postgresql(dot)org <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: concatenating hstores in a group by?

On Friday, January 17, 2025, Brent Wood <Brent(dot)Wood(at)niwa(dot)co(dot)nz<mailto:Brent(dot)Wood(at)niwa(dot)co(dot)nz>> wrote:

I want to concatenate the hstores,

There are no hstore aggregate functions. You’ll want to convert them to,json first then use the json_objectagg aggregate function.

David J.

[https://www.niwa.co.nz/static/niwa-2018-horizontal-180.png] <https://www.niwa.co.nz>
Brent Wood
Principal Technician - GIS and Spatial Data Management
Programme Leader - Environmental Information Delivery
+64-4-386-0529

National Institute of Water & Atmospheric Research Ltd (NIWA)
301 Evans Bay Parade Hataitai Wellington New Zealand
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