참고만 하셔서 더 좋은 쿼리 만들어 보세요.

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WITH WITH_DATA AS (
    SELECT 111 NO, 'A' GB, '홍길일' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'A' GB, '홍길이' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길삼' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길사' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길오' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'C' GB, '홍길육' NAME FROM DUAL
)

SELECT NO, GB
     , CASE WHEN COUNT(*) <= 1 THEN NAME
       ELSE
            NAME||'외'||(COUNT(*)-1)||'명'
       END NAME
  FROM (
    SELECT NO, GB
         , FIRST_VALUE(NAME) OVER (PARTITION BY NO, GB) NAME
      FROM WITH_DATA
  ) T
 GROUP BY NO, GB, NAME
 ORDER BY NO, GB;

 네 정말감사합니다

대표자 이름을 아무나 해도 상관이 없다면 아래처럼 구현해도 되지 않을까요?

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WITH WITH_DATA AS (
    SELECT 111 NO, 'A' GB, '홍길일' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'A' GB, '홍길이' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길삼' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길사' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'B' GB, '홍길오' NAME FROM DUAL UNION ALL
    SELECT 111 NO, 'C' GB, '홍길육' NAME FROM DUAL
)
SELECT NO, GB
     , CASE WHEN COUNT(*) <= 1 THEN MIN(NAME)
       ELSE
             MIN(NAME)||'외'||(COUNT(*)-1)||'명'
       END NAME
  FROM  WITH_DATA
 GROUP BY NO, GB
 ORDER BY NO, GB;