[프로그래머스]Lv5. 상품을 구매한 회원 비율 구하기

https://school.programmers.co.kr/learn/courses/30/lessons/131534

프로그래머스

문제

 

정답코드

SELECT YEAR, MONTH
    , COUNT(*) AS PUCHASED_USERS
    , ROUND((COUNT(*)/ (SELECT COUNT(*) 
                        FROM USER_INFO 
                        WHERE YEAR(JOINED) = 2021)), 1) AS PUCHASED_RATIO
FROM (
    SELECT DISTINCT YEAR(S.SALES_DATE) AS YEAR, MONTH(S.SALES_DATE) AS MONTH, U.USER_ID
    FROM ONLINE_SALE S JOIN USER_INFO U 
        ON S.USER_ID = U.USER_ID AND YEAR(JOINED) = 2021
) A
GROUP BY YEAR, MONTH
ORDER BY YEAR, MONTH