How to resolve the failure of connecting to an Oracle database using PL/SQL?

If the connection to the Oracle database fails in PL/SQL, you can try the following solutions:

1. Check the connection string: Ensure that the connection string contains the correct hostname, port number, database name and authentication information.
2. Check the network connection: Make sure that the network connection is working properly by pinging the database server to test the network connection.
3. Check the database status: Make sure the Oracle database is running and verify its status by connecting to it using SQL*Plus or other tools.
4. Check permissions: Ensure that the user connecting to the database has enough permissions to access database objects. You can use the sysdba user to check the user’s permissions.
5. Check the firewall settings: If there is a firewall or network security settings, make sure to allow the traffic from PL/SQL connecting to the database to pass through the firewall.
6. Check the listener: make sure that the Oracle listener is running and its configuration is correct.

If none of the above methods work to resolve the connection issue, you can try restarting the database service or reconfiguring the database connection information. If the problem persists, contact Oracle technical support for assistance.