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From: Brent Wood <[email protected]>
To: [email protected] <[email protected]>
Subject: Re: concatenating hstores in a group by?
Date: Sun, 19 Jan 2025 20:09:48 +0000
Message-ID: <SY7P300MB0761B08085ED0691EBA1B78DA1E42@SY7P300MB0761.AUSP300.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <CAKFQuwasxOzkA-BECEaOz1b8EOh2hGaEfcG3JHquL-eDJkSrMQ@mail.gmail.com>
References: <CH2PR01MB5765698BB9F71CEB662D5AE4AD1B2@CH2PR01MB5765.prod.exchangelabs.com>
	<[email protected]>
	<SY7P300MB0761A579730344B2813CA07DA11B2@SY7P300MB0761.AUSP300.PROD.OUTLOOK.COM>
	<CAKFQuwasxOzkA-BECEaOz1b8EOh2hGaEfcG3JHquL-eDJkSrMQ@mail.gmail.com>

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 <[email protected]>
Sent: Monday, January 20, 2025 04:28
To: Brent Wood <[email protected]>
Cc: [email protected] <[email protected]>
Subject: concatenating hstores in a group by?

On Friday, January 17, 2025, Brent Wood <[email protected]<mailto:[email protected]>> 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)
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