한쪽을 아래와 같이 변경후

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SELECT SUBSTR(MAX(SYS_CONNECT_BY_PATH(NAME,',')),2) NAME, CD
  FROM (SELECT ROW_NUMBER() OVER(PARTITION BY CD ORDER BY NAME) RN, CD, NAME
    FROM (
    SELECT 'A' CD, '가' NAME FROM DUAL UNION ALL
    SELECT 'A' CD, '나' NAME FROM DUAL UNION ALL
    SELECT 'A' CD, '다' NAME FROM DUAL UNION ALL
    SELECT 'A' CD, '라' NAME FROM DUAL UNION ALL
    SELECT 'B' CD, '마' NAME FROM DUAL UNION ALL
    SELECT 'B' CD, '바' NAME FROM DUAL))
 CONNECT BY RN = PRIOR RN + 1
   AND CD = PRIOR CD
 START WITH RN = 1  
 GROUP BY CD