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From: Rob Sargent <robjsargent@gmail.com>
To: Martin Norbäck Olivers <martin@norpan.org>
Cc: pgsql-sql@lists.postgresql.org
Subject: Re: get counts of multiple field values in a jsonb column
Date: Sat, 17 Oct 2020 10:15:12 -0600
Message-ID: <D96111AE-073A-4A0F-865A-BA34B57EC92C@gmail.com> (raw)
In-Reply-To: <CALoTC6sN0E_oYayqFYL1d=65N+C0P3ngnr=RvXo0=1=3fPpczA@mail.gmail.com>
References: <CALoTC6sN0E_oYayqFYL1d=65N+C0P3ngnr=RvXo0=1=3fPpczA@mail.gmail.com>



> On Oct 17, 2020, at 9:00 AM, Martin Norbäck Olivers <martin@norpan.org> wrote:
> 
> HI!
> I'm using postgres to store unstructured fields in a jsonb column. I also have a quite complicated query on the table, joining it with other tables etc, and given that query I want to get a count of all the values for a number of keys in the data.
> 
> Currently I'm doing one query for each key, like this
> select data->>'field1', count(*) from COMPLICATED QUERY group by 1
> select data->>'field2', count(*) from COMPLICATED QUERY group by 1
> ...
> select data->>'fieldN', count(*) from COMPLICATED QUERY group by 1
> 
> field1, field2, ..., fieldN are known at query time.
> 
> But as the number of keys I want to count for increases, so does the time it takes to run all these queries. I think the main problem is that COMPLICATED QUERY is complicated and takes time to run each time. I would very much like to run only one query that counts all the values of all the fields, but I'm not quite sure how to do that. I'm looking at all the aggregation functions but can't quite find one that suits this purpose.
> 
> I would love to get some input on ways to make this faster.
> 
> Regards,
> 
> Martin

If the “COMPLICATED QUERY” is repeated verbatim each time, run it once into a temp table and do the counts against the temp table.

create temp table complicate as COMPLICATED_QUERY;
/*maybe index*/
select data->>'field1', count(*) from COMPLICATED QUERY group by 1

You can put the whole thing in a function and drop the temp table each run.


A CTE based on COMPLICATED_QUERY might work too.

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