--create table poligonoval as 
select sum(valore) as valoreTOT, the_geom , nome_pre, cod_pre
from
(select v.the_geom
as the_geom, v.cod_pre, v.nome_pre0, v.nome_pre, area(intersection(v.the_geom, m.the_geom))*m.valori as valore
from aziende_pre v, valori m
where v.the_geom && m.the_geom and 
intersects(v.the_geom, m.the_geom)) as val
group by the_geom, nome_pre, cod_pre;