CREATE TABLE Products (product_name VARCHAR2, product_id VARCHAR2)
CREATE TABLE Order_items (product_id VARCHAR2)

Show all product names without an order.
SELECT product_name FROM Products EXCEPT SELECT T1.product_name FROM Products AS T1 JOIN Order_items AS T2 ON T1.product_id = T2.product_id
SELECT "product_name" FROM "Products" EXCEPT SELECT "T1"."product_name" FROM "Products" "T1" JOIN "Order_items" "T2" ON "T1"."product_id" = "T2"."product_id"