카테고리 별 도서 판매량 집계하기

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

프로그래머스

 

 

오답 : 

 

SELECT a.CATEGORY "CATEGORY", count(*) "TOTAL_SALES"
from book a join book_sales b on a.book_id = b.book_id
WHERE b.SALES_DATE BETWEEN '2022-01-01' AND '2022-01-31'
group by a.category
order by a.category

 

 

정답 :

SELECT a.CATEGORY "CATEGORY", SUM(b.SALES) "TOTAL_SALES"
FROM book a
         JOIN book_sales b ON a.book_id = b.book_id
WHERE b.SALES_DATE BETWEEN '2022-01-01' AND '2022-01-31'
GROUP BY a.CATEGORY
ORDER BY a.CATEGORY;

 

 

count 는 칼럼 갯수 !!

 

합계는 sum !!