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:

Answer 1

Also you can tranform json into text, concatenate, replace and convert back to json. Using the same data from Clément you can do:

SELECT replace(
    (json1::text || json2::text), 
    '}{', 
    ', ')::json 
FROM test

You could also concatenate all json1 into single json with:

SELECT regexp_replace(
    array_agg((json1))::text,
    '}"(,)"{|\\| |^{"|"}$', 
    '\1', 
    'g'
)::json
FROM test

This is a very old solution, since 9.4 you should use json_object_agg and simple || concatenate operator. Keeping here just for reference.