Joining DBA_HIST_ACTIVE_SESS_HISTORY with DBA_USERS

select
   count(*),
   ses.user_id,
   usr.username
from
   dba_hist_active_sess_history  ses                              left join
   dba_users                     usr on ses.user_id = usr.user_id
where
   usr.oracle_maintained = 'N'
group by
   ses.user_id,
   usr.username
order by  
   usr.username;