오프라인/온라인 판매 데이터 통합하기

SELECT DATE_FORMAT(SALES_DATE, '%Y-%m-%d') AS SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT
FROM ONLINE_SALE
WHERE SALES_DATE LIKE ('2022-03%')
UNION 
SELECT DATE_FORMAT(SALES_DATE, '%Y-%m-%d') AS SALES_DATE, PRODUCT_ID, NULL 'USER_ID', SALES_AMOUNT 
FROM  OFFLINE_SALE 
WHERE SALES_DATE LIKE ('2022-03%')
ORDER BY SALES_DATE, PRODUCT_ID, USER_ID;

#NULL 'USER_NAME' (SAME AS ) NULL AS USER_ID