WITH t AS
(
SELECT 1 pk, 'S0203' cd, '20121218' sdt, '20121219' edt FROM dual
UNION ALL SELECT 2, 'S0203', '20121226', '20121226' FROM dual
UNION ALL SELECT 3, 'S0203', '20121227', '20121228' FROM dual
UNION ALL SELECT 4, 'S0204', '20130129', '20130131' FROM dual
UNION ALL SELECT 5, 'S0204', '20130204', '20130220' FROM dual
UNION ALL SELECT 6, 'S0204', '20130221', '20130305' FROM dual
UNION ALL SELECT 7, 'S0204', '20130306', '99991231' FROM dual
)
SELECT MIN(pk) pk
     , cd
     , MIN(sdt) sdt
     , MAX(edt) edt
  FROM (SELECT pk, cd, sdt, edt
             , SUM(flag) OVER(PARTITION BY cd ORDER BY sdt) gb
          FROM (SELECT pk, cd, sdt, edt
                     , DECODE(LAG(edt) OVER(PARTITION BY cd ORDER BY sdt)
                       , TO_CHAR(TO_DATE(sdt, 'yyyymmdd') - 1, 'yyyymmdd')
                       , 0, 1) flag
                  FROM t
                )
        )
 GROUP BY cd, gb
 ORDER BY cd, gb
;