상품을 구매한 회원 비율 구하기

문제

코드

SELECT YEAR(O.SALES_DATE) AS YEAR, MONTH(O.SALES_DATE) AS MONTH,
    COUNT(DISTINCT O.USER_ID) AS PURCHASED_USERS,
    ROUND((COUNT(DISTINCT O.USER_ID)/
           (SELECT COUNT(*) FROM USER_INFO WHERE YEAR(JOINED) = 2021)),1) AS PURCHASED_RATIO
FROM ONLINE_SALE O
WHERE O.USER_ID IN (SELECT USER_ID FROM USER_INFO WHERE YEAR(JOINED) = 2021)
GROUP BY YEAR, MONTH
ORDER BY YEAR, MONTH;

 

출처: 프로그래머스 코딩 테스트 연습, https://school.programmers.co.kr/learn/courses/30/lessons/131534