▶학습내용문제1) SELECT U.USER_ID,U.NICKNAME,CONCAT(U.CITY,' ', U.STREET_ADDRESS1,' ', U.STREET_ADDRESS2) AS "전체주소" , CONCAT(SUBSTR(U.TLNO,1,3),'-', SUBSTR(U.TLNO,4,4),'-', SUBSTR(U.TLNO,8,4)) AS "전화번호 " FROM USED_GOODS_USER AS U INNER JOIN ( SELECT WRITER_ID FROM USED_GOODS_BOARD GROUP BY WRITER_ID HAVING CO..