What are the distinct ids of products ordered between 1975-01-01 and 1976-01-01??
select distinct t2.product_id from orders as t1 join order_items as t2 on t1.order_id = t2.order_id where t1.date_order_placed >= "1975-01-01" and t1.date_order_placed <= "1976-01-01"