프로그래머스 SQL 연습문제: 오프라인/온라인 판매 데이터 통합하기

SELECT SALES_DATE,
       PRODUCT_ID,
       USER_ID,
       SALES_AMOUNT
FROM ONLINE_SALE
WHERE SALES_DATE >= '2022-03-01'
  AND SALES_DATE < '2022-04-01'
UNION ALL
SELECT SALES_DATE,
       PRODUCT_ID,
       NULL AS USER_ID,
       SALES_AMOUNT
FROM OFFLINE_SALE
WHERE SALES_DATE >= '2022-03-01'
  AND SALES_DATE < '2022-04-01'
ORDER BY SALES_DATE, PRODUCT_ID, USER_ID;