WITH t AS
(
SELECT 1 seq, 'a' pt, '01.01' dt FROM dual
UNION ALL SELECT 2, 'a', '01.02' FROM dual
UNION ALL SELECT 3, 'a', '01.04' FROM dual
UNION ALL SELECT 4, 'b', '01.05' FROM dual
UNION ALL SELECT 5, 'a', '01.07' FROM dual
UNION ALL SELECT 6, 'a', '01.10' FROM dual
UNION ALL SELECT 7, 'b', '01.11' FROM dual
UNION ALL SELECT 8, 'c', '01.14' FROM dual
UNION ALL SELECT 9, 'c', '01.15' FROM dual
)
SELECT seq, pt
     , LAST_VALUE(dt IGNORE NULLS) OVER(ORDER BY seq DESC) dt
  FROM (SELECT seq, pt
             , DECODE(pt, LEAD(pt) OVER(ORDER BY seq), null, dt) dt
          FROM t
        )
 ORDER BY seq
;