[GROUPBY 2항, DATE, JOIN2개] 저자별 카테고리별 매출액 집계하기

https://school.programmers.co.kr/learn/courses/30/lessons/144856

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SELECT B.AUTHOR_ID, C.AUTHOR_NAME, B.CATEGORY, SUM(A.SALES*B.PRICE) AS SALES
FROM BOOK_SALES AS A
LEFT JOIN BOOK AS B ON A.BOOK_ID=B.BOOK_ID
LEFT JOIN AUTHOR AS C ON B.AUTHOR_ID = C.AUTHOR_ID
WHERE DATE_FORMAT(A.SALES_DATE,"%Y-%m")="2022-01"
GROUP BY B.AUTHOR_ID, CATEGORY
ORDER BY B.AUTHOR_ID ASC , CATEGORY DESC;