Migrate flat jsonb to hstore

Question

I run postgres 9.4, and want to migrate column in my database table to hstore just to be able to make performance comparison.

My current column is key-value pair in jsonb, w/o nested structure.

Any tips how to approach this problem?

Answer 1

Example data:

create table jsons (id int, val jsonb);
insert into jsons values
(1, '{"age":22}'), 
(2, '{"height":182}'),
(3, '{"age":30, "height":177}');

Split json objects to key, value pairs:

    select id, (jsonb_each_text(val)).key, (jsonb_each_text(val)).value
    from jsons

 id |  key   | value 
----+--------+-------
  1 | age    | 22
  2 | height | 182
  3 | age    | 30
  3 | height | 177
(4 rows)        

Aggregate the pairs and convert them to hstore:

select id, hstore(array_agg(key), array_agg(value))
from (
    select id, (jsonb_each_text(val)).key, (jsonb_each_text(val)).value
    from jsons
    ) sub
group by 1
order by 1

 id |            hstore            
----+------------------------------
  1 | "age"=>"22"
  2 | "height"=>"182"
  3 | "age"=>"30", "height"=>"177"
(3 rows)    

The same can be accomplished in a more elegant way using lateral join:

select id, hstore(array_agg(key), array_agg(value))
from jsons
cross join jsonb_each_text(val)
group by 1
order by 1;