Show the product name for all products.
select product_name from products
Show the product name and all the order quantities for each product.
select t1.product_name, t2.order_quantity from products as t1 join order_items as t2 on t1.product_id = t2.product_id
For each of those products, what is the total order quantity?
select t1.product_name, sum(t2.order_quantity) from products as t1 join order_items as t2 on t1.product_id = t2.product_id group by t1.product_id