SELECT trim(to_char(floor(((date1-date2)*24*60*60)/3600), '00')) || ':' ||
        trim(to_char(floor((((date1-date2)*24*60*60) - floor(((date1-date2)*24*60*60)/3600)*3600)/60), '00')) || ':' ||
        trim(to_char(round((((date1-date2)*24*60*60) - floor(((date1-date2)*24*60*60)/3600)*3600 -
         (floor((((date1-date2)*24*60*60) - floor(((date1-date2)*24*60*60)/3600)*3600)/60)*60) )), '00'))
         as time_difference
    FROM dates;