상품을 구매한 회원 비율 구하기

• 문제
  

• 정답

SELECT YEAR(O.SALES_DATE) YEAR, MONTH(O.SALES_DATE) MONTH, COUNT(DISTINCT O.USER_ID) PURCHASED_USERS, 
ROUND(COUNT(DISTINCT O.USER_ID) / (SELECT COUNT(USER_ID) 
                                      FROM USER_INFO 
                                      WHERE YEAR(JOINED) = 2021), 1) PUCHASED_RATIO
FROM USER_INFO U JOIN ONLINE_SALE O ON U.USER_ID = O.USER_ID
WHERE YEAR(U.JOINED) = '2021'
GROUP BY 1, 2
ORDER BY 1, 2

• 결과