oracle当前连接数，会话数



　1.查看session：
　　select * from v$session where username is not null
　　select username,count(username) from v$session where username is not null group by username
　2.当前连接数：
       select count(*) from v$process
　3.查看连接数参数的设置情况
　　select value from v$parameter where name = 'processes'
　　Select count(*) from v$session where status='ACTIVE'　#并发连接数