当我们接到一个任务对一个数据库进行优化时，有时候我们需要用到SYSTEM用户对数据库进行登陆，我们不能简单的把SYSTEM用户的密码修改了，因为其他管理人员有可能在使用这个用户，这是我们只需要把SYSTEM的密码临时变化一下，等优化结束后将其还原(当然前提是我们可以直接连接到服务器通过 / as sysdba方式作为sysdba进行登陆)。
SYSTEM用户的密码初始是:manager
[oracle@blliu ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Jan 25 21:04:07 2010
Copyright (c) 1982, 2007, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select password from dba_users where username='SYSTEM';
PASSWORD
------------------------------
D4DF7931AB130E37
SQL> alter user system identified by "1111";
User altered.
SQL> connect system/1111
Connected.
SQL> show user
USER is "SYSTEM"
SQL> connect sys/oracle as sysdba
Connected.
SQL> alter user system identified by values 'D4DF7931AB130E37';
User altered.
SQL> connect system/manager
Connected.
SQL> show user
USER is "SYSTEM"
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