-- Sessions by user
select username Usuario_Oracle, count(username) Numero_Sesiones
from v$session
group by username
order by Numero_Sesiones desc

select osuser, username, machine, program 
  from v$session 
  order by osuser

-- Order sessions by app
select program Aplicacion, count(program) Numero_Sesiones
from v$session
group by program 
order by Numero_Sesiones desc