sqlplus / as sysdba

显示parameter结构
SQL> set pause on
SQL> desc v$parameter

显示系统静态参数
SQL> select name from v$parameter where isses_modifiable = 'FALSE';

显示db_files是否可以用命令修改
SQL> select isses_modifiable, issys_modifiable, ismodified from v$parameter where name = 'db_files';

先查看db_files的原值，再用alter system修改，在显示修改后的值。
静态参数需要关闭实例重启后生效。
SQL> show parameter db_files

无法修改
SQL> alter system set db_files = 300;

并没有成功修改
SQL> alter system set db_files = 300 scope = spfile;
SQL> show parameter db_files

关闭实例后重启，修改成功
SQL> show parameter db_files
SQL> conn / as sysdba
SQL> startup

查看db-files的值
SQL> show parameter db_files

以下操作我还不清楚
SQL> conn scott/tiger
SQL> conn / as sysdba
SQL> alter user scott account unlock;
SQL> alter user scott identified by tiger;

显示startup命令的帮助信息
SQL> help startup

SQL> shutdown immediate
SQL> startup nomount
SQL> alter database mount;
SQL> alter database open;

SQL> shutdown immediate
SQL> startup mount

切换首先状态（首先状态只有有权限的管理员权限的用户才能访问数据库），分别尝试用scott和sys用户登录，观察系统提示的信息
SQL> shutdown immediate
SQL> startup restrict
//SQL> conn scott/tiger
SQL> conn / as sysdba
SQL> select * from scott.emp;

转为受限状态，权限不足
SQL> alter system disable restricted session;
SQL> conn scott/tiger
SQL> alter system enable restricted session;

SQL> shutdown immediate
SQL> conn / as sysdba
SQL> startup mount
SQL> alter database open read write;
SQL> delete from scott.emp where empnn = 7369;

SQL> select instance_name, active_state from v$instance;
SQL> alter system quiesce restricted;