[프로그래머스/5단계/MYSQL] 상품을 구매한 회원 비율 구하기

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

프로그래머스

 

SELECT YEAR(B.SALES_DATE) AS YEAR, MONTH(B.SALES_DATE) AS MONTH, COUNT(DISTINCT B.USER_ID) AS PUCHASED_USERS, 
ROUND(COUNT(DISTINCT B.USER_ID)/ (SELECT COUNT(*) FROM USER_INFO WHERE YEAR(JOINED)='2021') ,1) AS PUCHASED_RATIO
FROM USER_INFO A, ONLINE_SALE B
WHERE YEAR(A.JOINED)='2021' AND A.USER_ID=B.USER_ID
GROUP BY SUBSTR(B.SALES_DATE,1,7)
ORDER BY YEAR, MONTH;