문제 링크 : https://school.programmers.co.kr/learn/courses/30/lessons/131532 정상 코드. SELECT YEAR(SALES_DATE) AS YEAR, MONTH(SALES_DATE) AS MONTH, GENDER, COUNT(DISTINCT USER_ID) AS USERS FROM ONLINE_SALE JOIN USER_INFO USING (USER_ID) WHERE GENDER IS NOT NULL GROUP BY YEAR, MONTH, GENDER ORDER BY YEAR, MONTH, GENDER 내부 동작 순서 1. FROM 절 ONLINE_SALE 테이블과 USER_INFO 테이블을 USER_ID를 사용하여 조인합니다. 2. WHERE 절 GE..
