PostgreSQL connected component query

CREATE OR REPLACE FUNCTION choose_other(x bigint, y bigint, z bigint) RETURNS bigint AS
$$
SELECT CASE x
  WHEN y THEN z
    ELSE y
  END
$$ LANGUAGE SQL;

CREATE OR REPLACE FUNCTION node_connected_component(node_id bigint) RETURNS SETOF bigint AS
$$
WITH RECURSIVE n(id, path) AS (
  VALUES (node_id, ARRAY[node_id])
  UNION
  SELECT
    choose_other(n.id, l.src_node_id, l.dst_node_id),
    n.path || ARRAY[choose_other(n.id, l.src_node_id, l.dst_node_id)]
  FROM n, link AS l
  WHERE
    NOT choose_other(n.id, l.src_node_id, l.dst_node_id) = ANY (n.path)
    AND l.active
    AND (l.src_node_id = n.id OR l.dst_node_id = n.id)
) SELECT id from n;
$$ LANGUAGE SQL;