CREATE OR REPLACE FUNCTION array_sort_unique (ANYARRAY) RETURNS ANYARRAY
LANGUAGE SQL
AS $body$
SELECT ARRAY(
    SELECT DISTINCT $1[s.i]
    FROM generate_series(array_lower($1,1), array_upper($1,1)) AS s(i)
    ORDER BY 1
);
$body$;

UPDATE
  stamp
SET
  same_series = (
    SELECT array_to_json(
        array_sort_unique(
            ARRAY(
                SELECT
                  ss.catalogue_code
                FROM
                  same_series ss
                WHERE
                  ss.link_id IS NULL
                  AND
                  ss.stamp_id = ps.id

                UNION

                SELECT
                  s.catalogue_code
                FROM
                  same_series ss
                INNER JOIN
                  stamp s ON ss.link_id = s.id
                WHERE
                  ss.stamp_id = ps.id
            )
        )
    )
  )
FROM
  stamp ps
WHERE
  ps.id in (
    SELECT
      DISTINCT stamp_id
    FROM
      same_series
  )
;

DROP FUNCTION IF EXISTS array_sort_unique(ANYARRAY);