A3: 

  TOP 5 : les pays de rang <= à 5


N_NATIONKEY N_NAME     NB_DE_CLIENTS       RANG
----------- ---------- ------------- ----------
          9 INDONESIA             22          1
          3 CANADA                21          2
         10 IRAN                  20          3
         15 MOROCCO               20          3
          1 ARGENTINA             18          5
         22 RUSSIA                18          5
          7 GERMANY               18          5
          2 BRAZIL                18          5