Count field using fields at another tables

Question

Hi. I have invoice and deliveries:
Create table Invoices (
InvoiceID number primary key,
OrganizationName varchar2(30),
InvoiceDate date,
TotalPrice money
Create table Deliveries (
InvoiceID number,
ProductName varchar2(30),
ProductPrice money,
Amount number,
Second table has information about products with in invoice.
I would like not to count all Products:
Select InvoiseID ,COUNT(ProductPrice*Amount) as "Total invoice Price"
From somewhere
Where something has the same InvoiceID
Group by invoiceID
I want it to count automaticlly and put it in TotalPrice field. How can I do it?

Answer 1

some notes...
Create or replace Procedure CountInvoiceSums IS
begin
cursor c1 is
select *
from Invoices;
records number;
records=(select COUNT(*) from Invoices);
invoiceN varchar2(5);
for j 1..records
LOOP
--get invoice name:
invoiceN=
--change invoice Total price for
(select SUM(ProductPrice*Amount)
from Products p
where p.INVOICENAME=invoiceN)
END LOOP
end;
--=========================================
Create or replace trigger InvoiceTotalPrice
after update of ProductPrice on Products
call CountInvoiceSums;
Am I on the right way? If I am, I have 2 questions:
1)how to edit field in j record? delete old the add new?
2)how to get field in j record?
Thanks in advance.
P.S. please just advice not make for me, i want to lean it myself.