테이블명을 test, 각 칼럼명을 col1,col2,col3, 그리고 데이타가 순차적으로 insert 되었다고 가정하면,

SELECT DECODE (a.col1,
               NULL, (SELECT col1
                        FROM TEST
                       WHERE ROWID =
                                   (SELECT MAX (ROWID)
                                      FROM TEST
                                     WHERE ROWID <= a.ROWID AND col1 IS NOT NULL)),
               a.col1
              ) col1,
       col2,
       DECODE (a.col3,
               NULL, (SELECT col3
                        FROM TEST
                       WHERE ROWID =
                                   (SELECT MAX (ROWID)
                                      FROM TEST
                                     WHERE ROWID <= a.ROWID AND col3 IS NOT NULL)),
               a.col3
              ) col3
  FROM TEST a

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