"Oracle Error Collection": Ora-12154:tns: Unable to resolve the specified connection identifier

Believe that this error is not unfamiliar to everyone, as long as the installation of the use of Oracle estimates have encountered this problem, generally in the use of PL/SQL connection to the Oracle database occurs.
The cause of this error and the solution are various, I also repeatedly have encountered this problem, today, the ORA-12154 solution to summarize.

1, first look at the server side, Oracle services and monitoring services are started. Win+r, enter services.msc to view the service. Check whether the two services are running.

2, through the SQL plus connection to the database to try to exclude server errors. If the SQL plus connection succeeds, it means that there is no error in the installation process, the database is working correctly, and the error is in some configurations.

3, if the Sqlplus can successfully log in, prove that the server is not a problem, then start troubleshooting configuration, First look at the Oracle installation directory: D:\app\NiuNiu\product\11.2.0\dbhome_1\NETWORK\ADMIN The Tnsnames.ora file below is configured with the appropriate connection descriptor. This is to see if a new network service is configured.
Specific how to configure See blog: http://blog.csdn.net/u010028869/article/details/46652165

Also, note that the network service name, such as the DRP, cannot have spaces before, and there can be a blank line between the two services, but it cannot have whitespace. You may not recognize a space. As shown in the following:

4. Check the environment variable-system variable path, whether there is an Oracle installation directory: D:\app\NiuNiu\product\11.2.0\dbhome_1\bin; This variable is automatically generated when you install Oracle, so it's a good idea to look at it for insurance purposes.

5. If the Oracle 10g version is installed, open PL/sql, cancel login, find "Tools->preferences" in the Plsql Developer toolbar, locate Oracle in connection node of Oracle Home Select Oraclient10g_home1, save and close Plsql Developer as shown:

6, if it is oracle11g, you need to check whether the Oracle 32-bit client is installed, the appropriate environment variables are configured. Specific configuration See article: http://blog.csdn.net/u010028869/article/details/46647479

7, if the above methods are not effective after the attempt, then try to replace the Plsql version, it is possible to download Plsql and installed on the version of the Oracle database is incompatible.

Temporarily think of the solution on this, hope to help everyone!

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"Oracle Error Collection": Ora-12154:tns: Unable to resolve the specified connection identifier