LeetCode1251.SQL

select p.product_id, ifnull(round(sum(u.units *p.price) / sum(u.units), 2), 0) as average_price from Prices as p left join UnitsSold as u on u.product_id = p.product_id and u.purchase_date between p.start_date and p.end_date group by p.product_id;