Problem: 1251. 平均售价

👨‍🏫 参考题解（题目数据增强，代码只能过90%的点）

🍻 AC code

SELECT  p.product_id, ROUND(ifnull(SUM(units * price) / SUM(units), 0),2) AS average_price
FROM prices as p
LEFT JOIN unitsSold as u ON p.product_id = u.product_id
WHERE u.purchase_date BETWEEN p.start_date AND p.end_date or u.product_id is null
GROUP BY p.product_id