Hi Rodrigo,

> select
> coalesce(a1.id,a2.id,...,a12.id) as id,
> sum(iNvl(a1.value,0)+iNvl(a2.value,0)+...+iNvl(a12.value)) as value
> from table1 a1
> full outer join table2 a2 on a1.id = a2.id
> full outer join table3 a3 on a1.id = a3.id
> ...
> full outer join table12 a12 on a1.id = a12.id
> group by coalesce(a1.id,a2.id,...,a12.id)

I believe that with your sql construction firebird is going to be
unable to use indexs at all.

The best approach to me would be to merge all the tables into one,
create views based on that table if you require them to duplicate the
12 original tables.

Alternatively, you could use a stored procedure similar to this:

create procedure getData
returns (id integer, value double)
as
for select id, sum(value) from a group by id into :id, :value do
suspend;
for select id, sum(value) from a1 group by id into :id, :value do
suspend;
{ ... }
end;

then use the following sql to get the results:

select id, value from getdata() group by id;

I not promising it will be any faster however, but I think it will be!
I must emphesis that my first option is to me a far better solution (
I believe you could make the views updateable in this option)

Regards
Ian Newby