-- Oefening 1

SELECT order_num
FROM OrderItems
WHERE prod_id = 'RGAN01';


-- Oefening 2

SELECT cust_id
FROM Orders
WHERE order_num IN (20007,20008);


-- Oefening 3

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