View the current number of Oracle connections

How can I view the current number of connections in Oracle? You only need to use the following SQL statement to query it.
Select * from V $ session where username is not null

Select username, count (username) from V $ session where username is not null group by username # view the number of connections of different users

Select count (*) from V $ session # Number of connections

Select count (*) from V $ session where status = 'active' # number of concurrent connections

Show parameter Processes # maximum connection

Alter system set processes = value scope = spfile; restart database # modify connection

/Home/Oracle9i/APP/Oracle9i/dbs/init. ora

/Home/Oracle9i/APP/Oracle9i/dbs/spfilexxx. ora # open_cursor