今日分享，今天在银行待了一天，明天可以休息一下了，祝大家周末愉快！

如果大家看到以下几种写法，大家会有什么想法？有什么区别？
告诉大家，这几种写法默认都可以登录到数据库的。

$sqlplus xxx/xxx as sysdba
$sqlplus roidba/roidba as sysdba
$sqlplus / as sysdba
$sqlplus '！@#/!!! as sysdba'

这里有几个小知识点值得注意。
1、Oracle 默认使用系统认证，登录数据库
2、单引号在这里强调忽略所有特殊字符，这就是为什么有时候我们需要单引号，而有的时候不需要。

我们在做数据库备份的时候，有的时候用sys,有的时候用system,有的时候有业务用户来做逻辑备份，而我又不想把密码暴露出来的话，怎么办呢？
有不少朋友就是使用了expdp \'/ as sysdba\'
例如

$expdp \'/ as sysdba\' 

Export: Release 12.1.0.2.0 - Production on Fri Dec 15 22:42:17 2017

Copyright (c) 1982, 2014, Oracle and/or its affiliates.  All rights reserved.

Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options
Starting "SYS"."SYS_EXPORT_SCHEMA_01":  "/******** AS SYSDBA" 
Estimate in progress using BLOCKS method...
Total estimation using BLOCKS method: 0 KB
Processing object type SCHEMA_EXPORT/STATISTICS/MARKER
ORA-31655: no data or metadata objects selected for job
Job "SYS"."SYS_EXPORT_SCHEMA_01" completed with 1 error(s) at Fri Dec 15 22:42:43 2017 elapsed 0 00:00:24

哪里来的xxx用户，别被忽悠了哈

$sqlplus xxx/xxx as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Fri Dec 15 22:44:20 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options

SYS@orcl1> select user from dual;

USER
------------------------------
SYS

哪里来的！@#用户哈，这下大家应该理解了吧，眼见不一定为实，自己动手测试验证了，才能得出最终的结论。

$sqlplus '！@#/!!! as sysdba'

SQL*Plus: Release 12.1.0.2.0 Production on Fri Dec 15 22:45:35 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options

SYS@orcl1> select user from dual;

USER
------------------------------
SYS

SYS@orcl1>