11g : similar queries but different results !

Hi ,

I have two "similar" queries :

QUERY 1 : No rows returned

Select F1.ID_FACT
From FACTORIES F1
LEFT JOIN FACTORIES F2
ON F1.ID_FACT = F2.ID_FACT
Where F1.NO_REF = 62
and F2.NO_REF = 61
and F2.ID_FACT is null;
---------------------------

QUERY 2 : 1050 rows returned

Select F1.ID_FACT
From FACTORIES F1 , FACTORIES F2
Where F1.ID_FACT = F2.ID_FACT(+)
and F1.NO_REF = 62
and F2.NO_REF(+)= 61
and F2.ID_FACT is null;

Why QUERY 1 result is diffrent to QUERY 2 result !

Best regards.
GD.