[sql] How can I get the number of days between 2 dates in Oracle 11g?

I'm trying to find an integer number of days between two dates in Oracle 11g.

I can get close by doing

select sysdate - to_date('2009-10-01', 'yyyy-mm-dd') from dual

but this returns an interval, and I haven't been successful casting this to an integer.

Edit: Apparently in 10g, this returns the number of days as an integer.

• Full days between end of month and start of today, including the last day of the month:

  SELECT LAST_DAY (TRUNC(SysDate)) - TRUNC(SysDate) + 1 FROM dual
  

• Days between using exact time:

  SELECT SysDate - TO_DATE('2018-01-01','YYYY-MM-DD') FROM dual
  

Or you could have done this:

select trunc(sysdate) - to_date('2009-10-01', 'yyyy-mm-dd') from dual

This returns a NUMBER of whole days:

SQL> create view v as 
  2  select trunc(sysdate) - to_date('2009-10-01', 'yyyy-mm-dd') diff 
  3  from dual;

View created.

SQL> select * from v;

      DIFF
----------
        29

SQL> desc v
 Name                   Null?    Type
 ---------------------- -------- ------------------------
 DIFF                            NUMBER(38)

This will work i have tested myself.
It gives difference between sysdate and date fetched from column admitdate

  TABLE SCHEMA:
    CREATE TABLE "ADMIN"."DUESTESTING" 
    (   
  "TOTAL" NUMBER(*,0), 
"DUES" NUMBER(*,0), 
"ADMITDATE" TIMESTAMP (6), 
"DISCHARGEDATE" TIMESTAMP (6)
    )

EXAMPLE:
select TO_NUMBER(trunc(sysdate) - to_date(to_char(admitdate, 'yyyy-mm-dd'),'yyyy-mm-dd')) from admin.duestesting where total=300

You can try using:

select trunc(sysdate - to_date('2009-10-01', 'yyyy-mm-dd')) as days from dual