sql TNS:protocol adapter error

ORA-12560: TNS:protocol adapter error
此问题是由于oracle_sid没有设置或者设置错误导致的.
解决办法:  使用安装目录的sqlplus程序即可解决，因为系统里面装了ORCAL客户端！
1:cmd命令行上:
C:\> set ORACLE_SID=orcl
orcl是设置的instance名字
在命令行上连接sqlplus如下:
C:\Documents and Settings\ldwtxwh>sqlplus

SQL*Plus: Release 10.1.0.2.0 - Production on 星期日 12月 20 18:22:28 2009

Copyright (c) 1982, 2004, Oracle.  All rights reserved.

Enter user-name: system
Enter password:

Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL>
ok!连接完毕

2:C:\Documents and Settings\ldwtxwh>sqlplus

SQL*Plus: Release 10.1.0.2.0 - Production on 星期日 12月 20 18:33:31 2009

Copyright (c) 1982, 2004, Oracle.  All rights reserved.

Enter user-name: sys/admin@orcl as SYSDBA
或者：scott/tiger@orcl

Connected to:

Oracle Database10gEnterpriseEdition Release10.2.0.1.0 - Production

With the Partitioning, OLAP and Data Mining options

SQL>
ok!连接完毕
现在用你的sqlplus就可以连接登陆了.