1개 컬럼 인가요? 'D,A,B,C'
4개 컬럼 인가요? 'D', 'A', 'B', 'C'

앗 1개 컬럼입니다!

WITH t AS
(
SELECT 1 id, 'D,A,B,C' v FROM dual
UNION ALL SELECT 2, 'Z,W,X,Y' FROM dual
)
SELECT id
     , v
     , LISTAGG(x, ',') WITHIN GROUP(ORDER BY x) x
  FROM (SELECT id, v
             , REGEXP_SUBSTR(v, '[^,]+', 1, lv) x
          FROM t
             , (SELECT LEVEL lv FROM dual CONNECT BY LEVEL <= 9)
         WHERE lv <= REGEXP_COUNT(v, '[^,]+')
        )
 GROUP BY id, v
 ORDER BY id
;

감사합니다 덕분에 해결되었습니다