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SQL 이론] UNION_ALL

-- 코드를 입력하세요
SELECT DATE_FORMAT(SALES_DATE, '%Y-%m-%d') as SALES_DATE, PRODUCT_ID, USER_ID, SALES_AMOUNT
    FROM (
        SELECT O.SALES_DATE, O.PRODUCT_ID, O.USER_ID, O.SALES_AMOUNT
        FROM ONLINE_SALE O
        WHERE O.SALES_DATE >= '2022-03-01' AND O.SALES_DATE <'2022-04-01'
        
        UNION ALL
        
        SELECT F.SALES_DATE, F.PRODUCT_ID, NULL as USER_ID, F.SALES_AMOUNT
        FROM OFFLINE_SALE F
        WHERE F.SALES_DATE >= '2022-03-01' AND F.SALES_DATE <'2022-04-01'
    ) AS S
    ORDER BY SALES_DATE, PRODUCT_ID, USER_ID