[프로그래머스] 오프라인/온라인 판매 데이터 통합하기 Mysql

https://school.programmers.co.kr/learn/courses/30/lessons/131537

프로그래머스

(SELECT DATE_FORMAT(SALES_DATE, '%Y-%m-%d') AS SALES_DATE, PRODUCT_ID, NULL AS USER_ID, SALES_AMOUNT
FROM OFFLINE_SALE 
WHERE DATE_FORMAT(SALES_DATE, '%m') = '03')
UNION ALL
(SELECT DATE_FORMAT(SALES_DATE, '%Y-%m-%d') AS SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT
FROM ONLINE_SALE
WHERE DATE_FORMAT(SALES_DATE, '%m') = '03')
ORDER BY SALES_DATE, PRODUCT_ID, USER_ID;