>I think you'd have to do something like this:
>
>select customer, sum(invoices) from ;
>(select Customer, count(InvNum) as Invoices;
> from ActiveInvoices;
> group by Customer;
>union select Customer, count(InvNum) as Invoices;
> from HistInvoices;
> group by Customer;
> order by Customer)
>group by customer

And also, you'd have to do UNION ALL, on the chance that a customer might have as many active invoices as history invoices.