Oracle : find duplicate row and total duplicate

select column_name, count(column_name)
from table
group by column_name
having count (column_name) > 1;

Oracle : display all date in month

Here some example for show all date in current/before/after month or specific month

select to_char( add_months(trunc(sysdate,'MM'),-1) + level - 1, 'YYYYMMDD' ) from dual connect by level <= last_day(add_months(trunc(sysdate,'MM'),-1)) -  add_months(trunc(sysdate,'MM'),-1) + 1;

Above is before current month

select to_char( add_months(trunc(sysdate,'MM'),1) + level - 1, 'YYYYMMDD' ) from dual connect by level <= last_day(add_months(trunc(sysdate,'MM'),1)) -  add_months(trunc(sysdate,'MM'),1) + 1;

Above is after current month

select to_char( trunc(sysdate,'MM') + level - 1, 'YYYYMMDD' ) from dual connect by level <= last_day(trunc(sysdate,'MM')) -  trunc(sysdate,'MM') + 1;

Above is current month

select to_char( trunc(to_date('20140101','YYYYMMDD'),'MM') + level - 1, 'YYYYMMDD' ) from dual connect by level <= last_day(trunc(to_date('20140101','YYYYMMDD'),'MM')) -  trunc(to_date('20140101','YYYYMMDD'),'MM') + 1;

Above is specific month but you must enter date.