How to resolve the issue of PLSQL connecting to Oracle …

When the “no listener” error occurs, it may be due to the following reasons:

1. Oracle service is not started: make sure the Oracle service is started. You can check the status of the listener program by running the command “lsnrctl status” in the command prompt.
2. Listener program configuration error: Please verify the configuration in the listener.ora file is correct. This file is typically located in the $ORACLE_HOME/network/admin directory. Make sure the listener’s port number and service name are configured correctly.
3. Firewall or network issues: Make sure the firewall is not blocking the Oracle service port connection. If using a virtual machine or cloud server, also check that the network configuration is correct.
4. TNS path configuration error: Please check if the configuration in the tnsnames.ora file is correct. This file is usually located in the $ORACLE_HOME/network/admin directory. Make sure the hostname, port number, and service name in the TNS path are configured correctly.

The steps to solve this problem are as follows:

1. Check if the Oracle service is already started. If it is not started, please start the service.
2. Check the configuration of the listener program to ensure that the port number and service name are correct. You can use the command “lsnrctl status” to view the status of the listener program.
3. Check the firewall and network settings to ensure that the ports for Oracle service are not blocked.
4. Check the configuration in the tnsnames.ora file to ensure that the TNS path is correct.

If the above steps still cannot resolve the issue, it is recommended to consult an Oracle database administrator or technical support person for more detailed assistance.