[ SELECT 오프라인/온라인 판매 데이터 통합하기 ]

- UNION ALL / UNION

SELECT TO_CHAR(SALES_DATE, 'YYYY-MM-DD') AS SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT FROM 
(SELECT SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT FROM ONLINE_SALE 
UNION ALL
SELECT SALES_DATE, PRODUCT_ID, NULL AS USER_ID, SALES_AMOUNT FROM OFFLINE_SALE)
WHERE TO_CHAR(SALES_DATE, 'YYYYMM') = '202203'
ORDER BY SALES_DATE, PRODUCT_ID, USER_ID;

 

- UNION ALL 과 UNION의 차이 살펴봐야함