Oracle query for difference between two dates in hours

Oracle Query to calculate date difference in hours

Example: 1

SELECT floor(((to_date('01-jan-2012')-to_date('01-jun-2011'))*24*60*60)/3600) from dual;


Example 2:

Calculate diffence between any date from SYSDATE

Select trunc((Sysdate-to_date('06/19/2012 1:20:14','mm/dd/yyyy hh12:mi:ss'))*24) From dual;