postgresql - Merging Concatenating JSON(B) columns in query

Question

Using Postgres 9.4, I am looking for a way to merge two (or more) json or jsonb columns in a query. Consider the following table as an example:

  id | json1        | json2
----------------------------------------
  1   | {'a':'b'}   | {'c':'d'}
  2   | {'a1':'b2'} | {'f':{'g' : 'h'}}

Is it possible to have the query return the following:

  id | json
----------------------------------------
  1   | {'a':'b', 'c':'d'}
  2   | {'a1':'b2', 'f':{'g' : 'h'}}

Unfortunately, I can't define a function as described here. Is this possible with a "traditional" query?

Answer 1

In Postgres 9.5+ you can merge JSONB like this:

select json1 || json2;

Or, if it's JSON, coerce to JSONB if necessary:

select json1::jsonb || json2::jsonb;

Or:

select COALESCE(json1::jsonb||json2::jsonb, json1::jsonb, json2::jsonb);

(Otherwise, any null value in json1 or json2 returns an empty row)

For example:

select data || '{"foo":"bar"}'::jsonb from photos limit 1;
                               ?column?
----------------------------------------------------------------------
 {"foo": "bar", "preview_url": "https://unsplash.it/500/720/123"}

Kudos to @MattZukowski for pointing this out in a comment.