How can I get join results as JSON in a PostgreSQL query?

Question

I have the query below that almost works: It returns 3 rows one of which should have first_nation populated (other two should be NULL). But they all get the same data for first_nation. What I need is the person.id from the outer where to be a part of the WHERE in the inner query but I don't think that's doable. Any help would be appreciated.

Or another way, I'd like the results of the JOIN to be JSON rather than appearing as additional columns.

SELECT person.id,
  (
    SELECT row_to_json(x)
    FROM (
      SELECT ref_first_nations_gov.id
      FROM ref_first_nations_gov JOIN person ON person.first_nation_id = ref_first_nations_gov.id
      WHERE person.application_id = 1 AND person.archived = false
    ) x
  ) AS first_nation
FROM person
WHERE application_id = 1 AND archived = false;

EDIT: Sample Data

SELECT id, application_id, first_nation_id FROM person WHERE application_id = 1;
 id | application_id | first_nation_id 
----+----------------+-----------------
  4 |              1 |                
  1 |              1 |                
  2 |              1 |                
  3 |              1 |               1

What the query above gives me:

 id | first_nation 
----+--------------
  4 | {"id":1}
  1 | {"id":1}
  3 | {"id":1}

What I want

 id | first_nation 
----+--------------
  4 | 
  1 | 
  3 | {"id":1}

Answer 1

Even though I don't have how to test this right now, I don't think you need a subquery.

Try something like this.

SELECT p.id, row_to_json(r.id) FROM person p 
  FULL OUTER JOIN ref_first_nations_gov r on r.id = p.first_nation_id
  WHERE p.application_id = 1 AND p.archived = false;