-- Oefening 1

SELECT cust_id
FROM Orders
WHERE order_num IN (SELECT order_num
					FROM OrderItems
					WHERE prod_id = 'RGAN01');
					
-- Oefening 2

SELECT Orders.cust_id
FROM Orders
INNER JOIN OrderItems ON Orders.order_num = OrderItems.order_num 
WHERE OrderItems.prod_id='RGAN01';

SELECT O.cust_id
FROM Orders AS O
INNER JOIN OrderItems AS I ON O.order_num = I.order_num 
WHERE I.prod_id='RGAN01';

-- Oefening 3

SELECT O.cust_id
FROM Orders AS O, OrderItems AS I
WHERE O.order_num = I.order_num AND prod_id='RGAN01';