Final answer:
ORA-12154 is an error indicating that the Oracle database service name could not be resolved, often due to a misconfiguration in the tnsnames.ora file or a network issue. To fix it, check the tnsnames.ora file and network connectivity to the Oracle server.
Step-by-step explanation:
The ORA-12154 error message stands for 'TNS:could not resolve the connect identifier specified'. It is an error that occurs when the client is unable to connect to an Oracle database because it cannot resolve the database alias specified in the connection string. The cause of this error can typically be attributed to a misconfigured or missing tnsnames.ora file, incorrect entries within this file, or a network connectivity issue preventing access to the Oracle server.
To resolve this error, you should check the tnsnames.ora file, which is usually found in the 'network/admin' directory of your Oracle client installation. Ensure that it contains the correct service name, host, and port for the database you're trying to connect to. If the tnsnames.ora file is configured properly, verify that the database service is up and running, and you have network access to the Oracle server.