En modifiant la réponse à votre question précédente, donne ce qui suit...
WITH RECURSIVE sub(s_id, s_r_id, s_a_id, s_p_id, row) AS (
SELECT id, r_id, a_id, p_id, 1 AS row FROM foo WHERE p_id = 0
UNION ALL
SELECT id, r_id, a_id, p_id, (row + 1) FROM foo JOIN sub ON s_a_id = p_id AND s_r_id = r_id
)
SELECT * FROM sub ORDER BY s_r_id, row;