I have this query:

```
SELECT C.ID_PASS, C.ID_MERCE, CTRL.ESITO, M.ID_CAT, M.QTA, M.DESCRIZ, 
   CTRL.ID_PUNTO, CTRL.ID_ADDETTO, C.DATE_OPEN, C.DATE_CLOSE, C.NOTE

FROM   CONTESTAZIONI C, CONTROLLI CTRL, FUNZIONARI F, ADDETTI A, MERCI M

WHERE  A.ID=CTRL.ID_ADDETTO
  AND    A.ID_FUNZ=501
  AND    M.ID=C.ID_MERCE
  AND    M.ID_PASS=C.ID_PASS
  AND    CTRL.ESITO > 1
GROUP  BY C.ID_PASS;

```

Why, if I don't add `GROUP BY C.ID_PASS`, do I get 20 rows (instead of 2).