Merging Concatenating JSON(B) columns in query

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.