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。 [plain] view plaincopyprint? 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> 

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>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=testORACLE_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 . 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：