Getting the corresponding record of a Cursor/Select when in a Cursor LOOP statement - oracle

Question

The question seems easy. I have built a package, where there is a quite massive cursor, let's say on all invoices of my company for the whole year.
CURSOR c_invoices(p_year IN INTEGER) IS
SELECT all_invoices.invoicenumber,
all_invoices.invoicedate,
all_invoices.customernumber
FROM all_invoices
WHERE all_invoices.year = p_year
;
After opening it and using a LOOP statement, I want to get some data from another table (forbidden_customers), but only if the customer is in this very last table.
What I'd like to do, is to open another cursor (or a SELECT ?) at the very beginning of my package, browsing the whole table(forbidden_customers), and then getting to the corresponding record when in my invoices LOOP.
So, something like :
CURSOR c_forbidden_customers IS
SELECT forbidden_customers.customernumber,
forbidden_customers.customeradress
FROM forbidden_customers
;
And then :
OPEN c_invoices(v_year);
LOOP FETCH c_invoices INTO invoices_cursor;
BEGIN
EXIT WHEN c_invoices%NOTFOUND;
*IF invoices_cursor.customernumber IS FOUND IN c_forbidden_customers ...
THEN ...*
This is what I do meanwhile (I know it is bad):
SELECT COUNT(*)
INTO v_exist /*INTEGER*/
FROM forbidden_customers
WHERE forbidden_customers.customernumber= p_customernumber
IF v_exist <> 0
THEN...
I tried to make it as clear as possible. Thank you for your time

Answer 1

Don't do it twice; join both tables in the same cursor and use it. Also, if you switch to a cursor FOR loop, you'll save yourself from some typing as Oracle will do most of boring stuff for you (declaring cursor variable, opening the cursor, closing it, exiting the loop ...):
create or replace procedure p_test (p_year in integer) is
begin
for c_invoices in
(select a.invoicenumber,
a.invoicedate,
a.customernumber,
c.customeraddress
from all_invoices a join forbidden_customers c on c.customernumber = a.customernumber
where a.year = p_year)
loop
-- do something
end loop;
end;

Answer 2

If the table forbidden_customers is not large and it will fit oracle's session memory, you can use a pl/sql table to store all id's from forbidden_customers and check it later. The check is done in memory only, so it is much faster than any regular select.
create table all_invoices
(id number,
year number,
customer_number number);
create table forbidden_customers
(customer_number number);
CREATE OR REPLACE TYPE t_number_table IS TABLE OF number
/
CREATE OR REPLACE PROCEDURE test23
IS
forbidden_customers_list t_number_table;
CURSOR c_invoices (p_year IN INTEGER)
IS
SELECT all_invoices.customer_number
FROM all_invoices
WHERE all_invoices.year = p_year;
BEGIN
SELECT customer_number
BULK COLLECT INTO forbidden_customers_list
FROM forbidden_customers;
FOR rec_invoices in c_invoices(2022) loop
if forbidden_customers_list.exists(rec_invoices.customer_number) then
null;
end if;
end loop;
end;
/