>I have to sum two fields. Same field name but in two different tables.
>
>Right now I sum and join but I end-up with two sums for the same Id.
>
>How do I sum everything without intermediate sums (because of the joins) ?
>
>I guess that "where in (select...) would be involved but I'm sot sure how to build this.

Try:

SELECT somefield, SUM(Tbl1.Fld1 + Tbl2.Fld1) AS ???;
FROM Tbl1;
INNER JOIN Tbl2 ON ....
GROUP BY ...