有人给出的方法是sqlplus直接回车，然后在提示用户名时输入/ as sysdba：

[oracle@yans1 ~]$ sqlplus

SQL*Plus: Release 10.2.0.3.0 - Production on 星期六 8月 8 22:01:47 2009

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

Enter user-name: / as sysdba

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL>

其实在10g中，sqlplus做了改进，可以在sqlplus后面直接加上/ as sysdba，而不需要双引号或单引号：

[oracle@yans1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.3.0 - Production on 星期六 8月 8 22:05:14 2009

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL>

在9i中，sqlplus还没有这个功能，必须在/ as sysdba两边加上引号。

bash-2.03$ sqlplus / as sysdba
Usage: SQLPLUS [ [] [] [] ]
where ::= -H | -V | [ [-L] [-M ] [-R ] [-S] ]
        ::= [/][@] | / | /NOLOG
        ::= @|[.] [ ...]
        "-H" displays the SQL*Plus version banner and usage syntax
        "-V" displays the SQL*Plus version banner
        "-L" attempts log on just once
        "-M " uses HTML markup options
        "-R " uses restricted mode
        "-S" uses silent mode
bash-2.03$ sqlplus "/ as sysdba"

SQL*Plus: Release 9.2.0.4.0 - Production on 星期六 8月 8 22:25:16 2009

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.

Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production

SQL>

从这种小的变化也可以看出，对于Oracle最基础的sqlplus工具而言，也在不断的提高易用性。