[GROUP BY] 식품분류별 가장 비싼 식품의 정보 조회하기 (Oracle)

SELECT A.AUTHOR_ID
    , B.AUTHOR_NAME
    , A.CATEGORY
    , SUM(PRICE * SALES) AS TOTAL_SALES
FROM BOOK A, AUTHOR B, BOOK_SALES C
WHERE A.AUTHOR_ID = B.AUTHOR_ID
AND A.BOOK_ID = C.BOOK_ID
AND TO_CHAR(SALES_DATE, 'YYYYMM') = '202201'
GROUP BY  A.AUTHOR_ID
        , B.AUTHOR_NAME
        , A.CATEGORY
ORDER BY AUTHOR_ID, CATEGORY DESC
;