[Programmers] 021 - 저자 별 카테고리 별 매출액 집계하기

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