https://school.programmers.co.kr/learn/courses/30/lessons/144855
SELECT
book.category AS CATEGORY,
sum( book_sales.sales ) as TOTAL_SALES
FROM book
LEFT OUTER JOIN
book_sales
ON
book.book_id = book_sales.book_id
WHERE
book_sales.sales_date like '2022-01%'
GROUP BY
book.category
ORDER BY
book.category asc;