Mutex sleep in database - oracle database script

COLUMN mux format a18 heading 'Mutex Type' trunc;

COLUMN loc format a32 heading 'Location' trunc;

COLUMN sleeps format 9,
                     999,
                     999,
                     990 heading 'Sleeps';

COLUMN wt format 9,
                 999,
                 990.9 heading 'Wait  |Time (s)';

SELECT e.mutex_type mux ,
       e.location loc ,
       e.sleeps - nvl(b.sleeps, 0) sleeps ,
       (e.wait_time - nvl(b.wait_time, 0))/1000000 wt
FROM DBA_HIST_MUTEX_SLEEP b ,
     DBA_HIST_MUTEX_SLEEP e
WHERE b.snap_id(+) = &bid
  AND e.snap_id = &eid
  AND b.dbid(+) = e.dbid
  AND b.instance_number(+) = e.instance_number
  AND b.mutex_type(+) = e.mutex_type
  AND b.location(+) = e.location
  AND e.sleeps - nvl(b.sleeps, 0) > 0
ORDER BY e.wait_time - nvl(b.wait_time, 0) DESC;