LANGUAGE plpgsql

    AS $$

BEGIN

    RETURN new;

END;

$$;

    IF new.matched_label_id IS DISTINCT FROM old.matched_label_id THEN

        IF new.matched_label_id IS NOT NULL THEN

            IF new.matched_label_id = new.taxonlabel_id THEN -- self-reference

            ELSE -- propagate from matched label

                    SELECT canon_label_id

                    FROM taxonlabel

                    WHERE taxonlabel_id = new.matched_label_id

            AND taxonlabel_id != new.taxonlabel_id -- avoid infinite recursion

            ;

        ELSE -- no matched taxonlabel

        END IF;

    END IF;

    RETURN new;