Norbert wrote:

>execute block
>returns (reference varchar(10), due double precision, balance double
>precision)
>as
>begin
>balance = 0;
>for select
>reference,due
>from invoices into :reference, :due
>do begin
>balance = balance+due;
>suspend;
>end
>end

Thank you Norbert, that does look like the simplest solution till FB 3 is available.