How to populate calendar table in Oracle?

This is a simple and easy way to do it

with calendar as (
        select :startdate + rownum - 1 as day
        from dual
        connect by rownum < :enddate - :startdate
    )
select rownum as "S.No", to_date(day,'dd_mm_yyyy') as "Cal_Dt", to_char(day,'day') as "DayName"
from calendar

with calendar as (
        select rownum - 1 as daynum
        from dual
        connect by rownum < sysdate - to_date('1-jan-2010') + 1
    )
select to_date('1-jan-2010') + daynum as monthdate
from calendar
;

declare
  v_date date := to_date('20110101','yyyymmdd');
begin

   while v_date < sysdate + 720 loop

      insert into calender
      values ( v_date, to_char(v_date,'DAY'));

      v_date := v_date + 1;

   end loop;
   commit;

end;
/

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This is not best practice and you should use Allesandro Rossi's solution. This may only be useful if you're using Oracle 9i or earlier and populating a large table.