https://school.programmers.co.kr/learn/courses/30/lessons/131533

정답

SELECT
    PRODUCT_CODE,
    SUM(SALES_AMOUNT) * PRICE AS SALES
FROM
    PRODUCT
        JOIN OFFLINE_SALE USING(PRODUCT_ID)
GROUP BY
    PRODUCT_ID
ORDER BY
    SALES DESC, PRODUCT_CODE

간단해서 메모 생략