转载自：http://blog.csdn.net/pan_tian/article/details/7699469
这种问题一般是因为客户端不知道要连那个instance或者不知道要使用哪个TNS Alias
可能的原因1.服务没有起来
下边是Tom的一个Test Case来说明OracleServiceSID服务没有起来的话，是会引起ORA-12560错误的。
- C:\Documents and Settings\tkyte>sqlplus scott/tiger
- SQL*Plus: Release 10.1.0.4.0 - Production on Thu Sep 6 15:43:55 2007
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- Connected to:
- Oracle Database 10g Enterprise Edition Release 10.1.0.4.0 - Production
- With the Partitioning, OLAP and Data Mining options
- scott%ORA10GR1> exit
- Disconnected from Oracle Database 10g Enterprise Edition Release 10.1.0.4.0 - Production
- With the Partitioning, OLAP and Data Mining options
- C:\Documents and Settings\tkyte>net stop oracleserviceora10gr1
- The OracleServiceORA10GR1 service is stopping.........
- The OracleServiceORA10GR1 service was stopped successfully.
- C:\Documents and Settings\tkyte>sqlplus scott/tiger
- SQL*Plus: Release 10.1.0.4.0 - Production on Thu Sep 6 15:44:35 2007
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- ERROR:
- ORA-12560: TNS:protocol adapter error
- Enter user-name:
- ERROR:
- ORA-12560: TNS:protocol adapter error
- Enter user-name:
- ERROR:
- ORA-12560: TNS:protocol adapter error
- SP2-0157: unable to CONNECT to ORACLE after 3 attempts, exiting SQL*Plus
- C:\Documents and Settings\tkyte>net start oracleserviceora10gr1
- The OracleServiceORA10GR1 service is starting..........
- The OracleServiceORA10GR1 service was started successfully.
- C:\Documents and Settings\tkyte>sqlplus scott/tiger
- SQL*Plus: Release 10.1.0.4.0 - Production on Thu Sep 6 15:45:12 2007
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- Connected to:
- Oracle Database 10g Enterprise Edition Release 10.1.0.4.0 - Production
- With the Partitioning, OLAP and Data Mining options
- scott%ORA10GR1><a name="PAGETOP"></a>
修改方法：控制面板>管理工具>服务里边把OracleServiceSID起起来
可能的原因2.ORACLE_SID环境变量没有指定（最常见引起ORA-12560问题的原因）
检查方法，命令行(cmd)下，
C:\Documents and Settings\ptian>set oracle_sid
ORACLE_SID=test
ORACLE_SID=test
ORACLE_SID是sqlplus默认连接的数据库instance,即sqlplus user/pwd连接的instance，如果不指定sqlplus里连接的时候就需要明确@你的instance,eg,sqlplus user/pwd@instance.
修改方法：在注册表中，HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraDb10g_home1\ORACLE_SID 需指向你的Instance(eg.orcl)；或者在系统的环境变量里加ORACLE_SID项，值为Instance的SID。
可能的原因3.TNS_ADMIN环境变量没有指定
检查方法，命令行(cmd)下，
C:\Documents and Settings\ptian>set TNS_ADMIN
TNS_ADMIN=D:\oracle\product\10.1.0\Db_1\NETWORK\ADMIN
TNS_ADMIN=D:\oracle\product\10.1.0\Db_1\NETWORK\ADMIN
TNS_ADMIN应该返回你的tnsnames.ora所在的目录
修改方法：可以在注册表HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0\TNS_ADMIN或者环境变量中指定。
可能的原因4.ORACLE_HOME环境变量没有指定
和上边的方法类似，检查Oracle_Home环境变量
可能的原因5.tnsnames.ora文件内容不对
A sample:
TEST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = ptian-cn.cn.oracle.com)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = test)
)
)
Possible fixes for the TNS-12560 include：
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = ptian-cn.cn.oracle.com)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = test)
)
)
Possible fixes for the TNS-12560 include：
