-- 어찌 성공하신건지 궁금하네요.
-- 저는 아무리 테스트해봐도 오류나는데요.
WITH t AS
(
SELECT LPAD('1', 2000, '1') v FROM dual
UNION ALL SELECT LPAD('2', 2000, '2') FROM dual
UNION ALL SELECT LPAD('3', 2000, '3') FROM dual
)
SELECT wm_concat(TO_CLOB(v))
  FROM t
;

WITH
TAB AS (
SELECT COD
   ,LPAD(COD + LVL,5) VAL
 FROM (
  SELECT 10000 COD FROM DUAL UNION ALL
  SELECT 20000 COD FROM DUAL UNION ALL
  SELECT 30000 COD FROM DUAL
  ) ,(
  SELECT LEVEL LVL
   FROM DUAL
   CONNECT BY LEVEL <= 5000
  )
)

-- 묶음 처리했습니다.
-- WM_CONCAT, LISTAGG 가 안되어서 XMLAGG 사용
-- (5:칼럼크기 + 1:구분자) * 5,000:최대ROW수 = 30,000:CONCAT한크기
-- 30,000 / 4,000:VARCHAR2크기 = 7.5 , 여유있게 10 묶음 처리
SELECT COD
   ,TO_CLOB(MAX(DECODE(NTL, 1 ,SUBSTR(VAL,2)))) ||
    TO_CLOB(MAX(DECODE(NTL, 2 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 3 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 4 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 5 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 6 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 7 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 8 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL, 9 ,VAL))) ||
    TO_CLOB(MAX(DECODE(NTL,10 ,VAL))) VAL
 FROM ( 
  SELECT COD ,NTL
     ,SUBSTR(XMLAGG(XMLELEMENT(V ,',' ,VAL) ORDER BY VAL).EXTRACT('//text()') ,1) VAL
   FROM (
    SELECT COD ,VAL
       ,NTILE(10) OVER (PARTITION BY COD ORDER BY VAL) NTL
     FROM TAB
     ORDER BY COD ,VAL
    )
   GROUP BY COD ,NTL
  )
 GROUP BY COD