Calculate difference between 2 date / times in Oracle SQL

Calculate difference between 2 date / times in Oracle SQL
select (to_date('2009-07-07 22:00', 'YYYY-MM-DD hh24:mi') - to_date('2009-07-07 19:30', 'YYYY-MM-DD hh24:mi')) diff_hours from dual;
date difference between oracle using todate function

Questions List - Database