Allen's 데이터 맛집

문제 풀이 -- 온라인 판매 데이터 SELECT DATE_FORMAT(sales_date, '%Y-%m-%d') AS sales_date, product_id, user_id, sales_amount FROM online_sale WHERE sales_date BETWEEN '2022-03-01' AND '2022-03-31' UNION ALL -- 오프라인 판매 데이터 SELECT DATE_FORMAT(sales_date, '%Y-%m-%d') AS sales_date, product_id, NULL AS user_id, sales_amount FROM offline_sale WHERE sales_date BETWEEN '2022-03-01' AND '2022-03-31' ORDER BY sales_d..