Find number of concurrent_users connected to Oracle apps

select count(distinct d.user_name) from apps.fnd_logins a, v$session b, v$process c, apps.fnd_user d
where b.paddr = c.addr and a.pid=c.pid and a.spid = b.process and d.user_id = a.user_id
and (d.user_name = ‘USER_NAME’ OR 1=1)