[UNION] 오프라인/온라인 판매 데이터 통합하기

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

프로그래머스

레벨4

SELECT DATE_FORMAT(SALES_DATE,"%Y-%m-%d") AS SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT 
FROM ONLINE_SALE AS B
WHERE DATE_FORMAT(SALES_DATE,"%Y-%m") LIKE "2022-03%"
 
UNION

SELECT SALES_DATE, PRODUCT_ID, NULL AS USER_ID, SALES_AMOUNT 
FROM OFFLINE_SALE AS B
WHERE DATE_FORMAT(SALES_DATE,"%Y-%m") LIKE "2022-03%"

ORDER BY SALES_DATE ASC, PRODUCT_ID ASC, USER_ID ASC;

 

UNION 후에 ORDER BY는 합쳐서 하나만!