SQL & PL/SQL

Hi

I have the following table relationship

Father -< Child -< GrandChild

Every table has numeric values that I would like to summarize but I have only one query:

select ...
from Father, Child, GrandChild
where Father.id = Child.parentId(+) and
Child.id = GrandChild.parentId(+)

In this query I would like to summarize values from Child and GrandChild. But if I summarize Child values they will be repeated depending on the number of GrandChild he has. So is there a way to do a "SUM" that will only summarize the values in Child without values repeating? SUM DISTINCT will not work because I can have values in two Childs that are equal.

Regards,

Néstor Boscán