Unknown database cmd_online： String url = jdbcmysql121199692483306cmd_online; String username = root; String password = YWRtaW42NjY=mysql; try Connection conn = DriverManagergetC

The error message "Unknown database 'cmd_online'" suggests that the database named "cmd_online" does not exist on the MySQL server at the specified IP address and port. It could be that the database has not been created yet, or that the IP address or port is incorrect. Double-check that the MySQL server is running and that the database has been created with the correct name and credentials.