Dear Group,

I need your help please, to optimize a query in FireBird.

I'm writing an Invoicing program. The Invoice Metadata is stored in
one table, and multiple items for each invoice are stored in a
separate table, like:

TABLE Invoices -> InvoiceID, CustomerName, CustomerAddress, etc.
TABLE InvoiceItems -> ItemID, InvoiceID, ItemName, ItemNetPrice,
VATPercentage and so on for each invoice item.

I would like to create a stored procedure which returns all of the
invoices, and calculates the invoice sum, vat sum, and total sum for
each invoice.

So I have the following queries:

Query1:
FOR SELECT InvoiceID, CustomerName, CustomerAddress
FROM Invoices INTO :InvoiceID, :CustomerName, :CustomerAddress
DO SUSPEND;

Query2:
SELECT Sum(ItemNetPrice * Quantity), Sum(ItemNetPrice * Quantity *
VATPercentage / 100), Sum(ItemNetPrice * Quantity * (1 +
VATPercentage / 100))
FROM InvoiceItems WHERE InvoiceID = :InvoiceID GROUP BY ItemID;

How could I combine these querys into one single query, so I won't
have to execute Query2 for each line of Query1?

Thank you!