Lv.3_카테고리 별 도서 판매량 집계하기

https://school.programmers.co.kr/learn/courses/30/lessons/144855

프로그래머스

SELECT B.CATEGORY, SUM(S.SALES) TOTAL_SALES
FROM BOOK B INNER JOIN BOOK_SALES S
ON B.BOOK_ID = S.BOOK_ID
WHERE EXTRACT(MONTH FROM S.SALES_DATE) = 1
GROUP BY B.CATEGORY
ORDER BY 1;