
1. 셀프 조인을 이용SELECT DISTINCT A.USER_ID, A.PRODUCT_IDFROM ONLINE_SALE as AJOIN ONLINE_SALE as BWHERE 1=1 AND A.USER_ID = B.USER_ID AND A.PRODUCT_ID = B.PRODUCT_ID AND A.SALES_DATE B.SALES_DATEORDER BY A.USER_ID ASC, A.PRODUCT_ID DESC 2. GROUP BY 사용SELECT USER_ID, PRODUCT_IDFROM ONLINE_SALEGROUP BY USER_ID, PRODUCT_IDHAVING COUNT(DISTINCT SALES_DATE) >= 2ORDER BY USER_ID ASC, PRODUCT_ID D..