How do you start up an Oracle database?

To start the Oracle database, you need to follow these steps:

1. Open the command prompt (Windows) or terminal (Linux).
2. Navigate to the “bin” directory in the Oracle software installation directory using the “cd” command. For example, if your Oracle software is installed in the “C:\Oracle” directory, you would need to enter the following command: cd C:\Oracle\bin.
3. Enter the command “sqlplus / as sysdba” to log in to the database as a system administrator. If you are using a non-Windows operating system, use the command “sudo sqlplus / as sysdba.”
4. Enter the “startup” command to initiate the database. If the database is already running, there will be no output. If the database is closed, it will be started and a message saying “Database opened” will be displayed.
5. You can use other commands to verify if the database has successfully started, such as “select status from v$instance;” or “select open_mode from v$database;”.
6. If you need to stop the database, use the “shutdown” command in step 3.

Please note that starting the Oracle database requires the appropriate permissions and the correct installation and configuration of the Oracle software. If you encounter any issues, refer to the official Oracle documentation or consult with a database administrator.