PostgreSQL|Beats 98%|Simple solution with LEFT JOIN
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nSELECT p.product_id,\n       COALESCE(ROUND(SUM(u.units * p.price)::decimal / SUM(u.units), 2), 0) average_price\nFROM prices p\n         LEFT JOIN unitssold u ON p.product_id = u.product_id\n    AND u.purchase_date BETWEEN p.start_date AND p.end_date\nGROUP BY p.product_id\n```
['PostgreSQL']