postgresql renvoie 0 si la valeur renvoyée est nulle

Question

J'ai une requête qui renvoie moy(prix)

  select avg(price)
  from(
      select *, cume_dist() OVER (ORDER BY price desc) from web_price_scan
      where listing_Type='AARM'
        and u_kbalikepartnumbers_id = 1000307
        and (EXTRACT(Day FROM (Now()-dateEnded)))*24 < 48
        and price>( select avg(price)* 0.50
                    from(select *, cume_dist() OVER (ORDER BY price desc)
                         from web_price_scan
                         where listing_Type='AARM'
                           and u_kbalikepartnumbers_id = 1000307
                           and (EXTRACT(Day FROM (Now()-dateEnded)))*24 < 48
                        )g
                   where cume_dist < 0.50
                 )
        and price<( select avg(price)*2
                    from( select *, cume_dist() OVER (ORDER BY price desc)
                          from web_price_scan
                          where listing_Type='AARM'
                            and u_kbalikepartnumbers_id = 1000307
                            and (EXTRACT(Day FROM (Now()-dateEnded)))*24 < 48
                        )d
                    where cume_dist < 0.50)
     )s

  having count(*) > 5

comment le faire retourner à 0 si aucune valeur n'est disponible ?