题目链接：点击打开链接
题目大意：略。
解题思路：略。
AC 代码
SELECT p.product_id, ROUND(SUM(price * units) / SUM(units), 2) average_price
FROM Prices p JOIN UnitsSold u ON p.product_id = u.product_id AND u.purchase_date BETWEEN start_date AND end_date
GROUP BY p.product_id
