Deep jsonb_concat for Postgres

deep_jsonb_concat.sql

-- Postgres jsonb_concat() function only merges the top level keys, it does not merge nested objects.
-- This will merge all nested objects. Note that it doesn't recurse through arrays, nor does it append
-- arrays, it simply replaces them. It would be easy to adjust this if you need. Tested on 9.6.
-- NOTE: This was mostly an experiment and has not been thoroughly vetted for functionality or performance,
-- use at your own risk!
-- This work is in the Public Domain.
CREATE OR REPLACE FUNCTION _deep_jsonb_concat(a jsonb, b jsonb) RETURNS jsonb AS $$
    DECLARE
        key text;
        merged jsonb;
    BEGIN
        if jsonb_typeof(a) <> 'object' THEN
            return b;
        end if;
        if jsonb_typeof(b) <> 'object' THEN
            return b;
        end if;
        merged := a;
        FOR key in SELECT jsonb_object_keys(b) LOOP
            merged := jsonb_set(merged, ARRAY[key], _deep_jsonb_concat(
                jsonb_object_field(a, key),
                jsonb_object_field(b, key)
            ));
        END LOOP;
        RETURN merged;
    END;
$$ LANGUAGE plpgsql;


SELECT jsonb_concat('{"a":{"nested":1}}'::jsonb, '{"a":{"also nested":2}}'::jsonb); -- {"a": {"also nested": 2}}
SELECT _deep_jsonb_concat('{"a":{"nested":1}}'::jsonb, '{"a":{"also nested":2}}'::jsonb); -- {"a": {"nested": 1, "also nested": 2}}

Thanks to this for some inspiration: https://gist.github.com/phillip-haydon/54871b746201793990a18717af8d70dc