Oracleでカレンダーテーブルを作成する方法

connect by level 句を使用できます:

 select FromDate+level-1 "Date", Description "HolidayName"
   from holiday 
connect by level <=  ToDate - FromDate + 1
  group by FromDate+level-1, Description
  order by 1;
  

 デモ