sum() problems

[PaT!]

Dear All,
 
I have this two queries
 
The first one gives me the right result for the sum():
 
SELECT           DATE_FORMAT(ordini.dataord,'%d-%m-%Y'), 
                        SUM(ordini.totale),
                        SUM(ordini.quantita),
                        ordini.codcliente,
                        ordini.fromprev
FROM              ordini
WHERE           ordini.numordine = 2302 
GROUP BY      ordini.numordine;
 
 
this other one gives me problems with the sum(), wrong result.
 
SELECT           DATE_FORMAT(ordini.dataord,'%d-%m-%Y'), 
                        SUM(ordini.totale),
                        SUM(ordini.quantita),
                        ordini.codcliente,
                        ordini.fromprev,
                        carello.numprev,
                        DATE_FORMAT(carello.dataordine,'%d-%m-%Y') 
FROM              ordini, carello 
WHERE           ordini.numordine = 2302 
AND                 carello.numprev = ordini.fromprev 
GROUP BY      ordini.numordine, carello.numprev;
 
Help is appreciated
 
I'm using mysql 4.0.13
 
Patrizio