SELECT DOTAZ2.KLIENT, DOTAZ2.ODBER, DOTAZ1.PRUMER
FROM
(select	 KLIENT.NAZEV_KL as KLIENT,
         SUM(ODECTY.KON_STAV-ODECTY.POC_STAV) as ODBER
   from	 ODECTY, MERIDLO, KLIENT
  where  MERIDLO.ID_KLIENTA =KLIENT.ID_KLIENTA 
    and	 MERIDLO.OZN_MERIDLA =ODECTY.OZN_MERIDLA
   and ODECTY.ID_OBD = 1
   group by KLIENT.NAZEV_KL) DOTAZ2,
(select	 avg(ODECTY.KON_STAV-ODECTY.POC_STAV) as PRUMER 
   from	 ODECTY  WHERE ID_OBD = 1) DOTAZ1
where DOTAZ2.ODBER > DOTAZ1.PRUMER