Oracleは連続した日付ブロックでデータを選択します

「ギャップと島」の問題のようです：

WITH cte("hash","date") AS (
    SELECT 'abcd',  DATE'2017-11-01' FROM dual UNION ALL
    SELECT 'abcd',  DATE'2017-11-02' FROM dual UNION ALL
    SELECT 'abcd',  DATE'2017-11-03' FROM dual UNION ALL
    SELECT 'wxyz',  DATE'2017-11-04' FROM dual UNION ALL
    SELECT 'wxyz',  DATE'2017-11-05' FROM dual UNION ALL
    SELECT 'abcd',  DATE'2017-11-06' FROM dual UNION ALL
    SELECT 'wxyz',  DATE'2017-11-07' FROM dual UNION ALL
    SELECT 'abcd',  DATE'2017-11-08' FROM dual UNION ALL
    SELECT 'abcd',  DATE'2017-11-09' FROM dual UNION ALL
    SELECT 'lmno',  DATE'2017-11-10' FROM dual UNION ALL
    SELECT 'lmno',  DATE'2017-11-11' FROM dual 
)
select "hash"
      ,min("date") as startdate
      ,max("date") as enddate
from (
    select "date","hash"
         , row_number() over (order by "date") 
         - row_number() over (partition by "hash" order by "date") as grp
    from cte
) A
group by "hash", grp
ORDER BY startdate;

DBFiddleデモ