Thread

1. get counts of multiple field values in a jsonb column

   Martin Norbäck Olivers <martin@norpan.org> — 2020-10-17T15:00:05Z

   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
   

2. Re: get counts of multiple field values in a jsonb column

   David G. Johnston <david.g.johnston@gmail.com> — 2020-10-17T15:38:50Z

   On Sat, Oct 17, 2020 at 8:00 AM Martin Norbäck Olivers <martin@norpan.org>
   wrote:
   
   > 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.
   >
   
   If you want counts the count function is your goto aggregate function.
   What you are missing is performing conditional counting.
   
   SELECT fld, count(*) FILTER (WHERE expression) FROM query GROUP BY fld;
   
   https://www.postgresql.org/docs/13/sql-expressions.html#SYNTAX-AGGREGATES
   
   David J.
   

3. Re: get counts of multiple field values in a jsonb column

   Rob Sargent <robjsargent@gmail.com> — 2020-10-17T16:15:12Z

   
   > 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.
   
   
   

4. Re: get counts of multiple field values in a jsonb column

   Simon Riggs <simon@2ndquadrant.com> — 2020-10-20T08:56:42Z

   On Sat, 17 Oct 2020 at 16:00, 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.
   
   You want something like this...
   
   select key, count(*) from (select (jsonb_each_text(data)).key from
   COMPLICATED QUERY) as kv group by 1;
   
   -- 
   Simon Riggs                http://www.EnterpriseDB.com/