Merging JSONB values in PostgreSQL?

Question

Using the || operator yields the following result:

select \'{\"a\":{\"b\":2}}\'::jsonb || \'{\"a\":{\"c\":3}}\'::jsonb ;
    ?column?     
-----         


        

Answer 1

This kind of "deep merge" can be interpreted quite differently, depending on your use case. For completeness, my intuition usually dictates the following rules:

• object + object: Every property survives from each object, which is not in the other object (JSON's null value is considered to be in the object, if it's explicitly mentioned). When a property is in both objects, the merge continues recursively with the same rules (this point is usually agreed on).
• array + array: The result is the concatenation of the two arrays.
• array + primitive/object: the result is the first array, with the second JSON value appended to it.
• any other cases: The result is the second JSON value (so f.ex. primitives or incompatible types override each other).

---

create or replace function jsonb_merge_deep(jsonb, jsonb)
  returns jsonb
  language sql
  immutable
as $func$
  select case jsonb_typeof($1)
    when 'object' then case jsonb_typeof($2)
      when 'object' then (
        select    jsonb_object_agg(k, case
                    when e2.v is null then e1.v
                    when e1.v is null then e2.v
                    else jsonb_merge_deep(e1.v, e2.v)
                  end)
        from      jsonb_each($1) e1(k, v)
        full join jsonb_each($2) e2(k, v) using (k)
      )
      else $2
    end
    when 'array' then $1 || $2
    else $2
  end
$func$;

This function's added bonus is that it can be called with literally any type of JSON values: always produces a result & never complains about JSON value types.

http://rextester.com/FAC95623