1、查询oracle的连接数select count(*) from v$session;2、查询oracle的并发连接数select count(*) from v$session where status='ACTIVE';3、查看不同用户的连接数select username,count(username) from v$session where username is not null group by username;4、查看所有用户：select * from all_users;5、查看用户或角色系统权限(直接赋值给用户或角色的系统权限)：select * from dba_sys_privs;select * from user_sys_privs;6、查看角色(只能查看登陆用户拥有的角色)所包含的权限select * from role_sys_privs;7、查看用户对象权限：select * from dba_tab_privs;select * from all_tab_privs;select * from user_tab_privs;8、查看所有角色：select * from dba_roles;9、查看用户或角色所拥有的角色：select * from dba_role_privs;select * from user_role_privs;10、查看哪些用户有sysdba或sysoper系统权限(查询时需要相应权限)select * from V$PWFILE_USERS;当前连接数：select count(*) from v$session;最大连接数：select value from v$parameter where name = 'processes';      修改最大连接数:      alter system set processes = 300 scope = spfile;      重启数据库:shutdown immediate;startup;