USING & NATURAL JOIN

-- INNER JOIN
SELECT order_date, product_name, ship_country, products.unit_price, quantity, discount
FROM orders
INNER JOIN order_details ON orders.order_id = order_details.order_id
INNER JOIN products ON order_details.product_id = products.product_id

-- USING
SELECT order_date, product_name, ship_country, products.unit_price, quantity, discount
FROM orders
INNER JOIN order_details USING(order_id) -- ON orders.order_id = order_details.order_id
INNER JOIN products USING (product_id) -- ON order_details.product_id = products.product_id

NATURAL JOIN is better not to use.

-- NATURAL JOIN
SELECT order_date, product_name, ship_country, products.unit_price, quantity, discount
FROM orders
NATURAL JOIN order_details
NATURAL JOIN products