When closing the database, you must have the SYSOPER OR SYSDBA permission. There are several ways to close the database:

1- NORMAL.

2- TRANSACTIONAL.

3- IMMEDIATE.

4- ABORT.

1- NORMAL:

This is the default mode for closing the database. During closing, the following steps occur:-

• No new user connection to the database is allowed.

• All users are waited to end their connection before completing the database closing.

• All data in the buffer must be written to disk.

• Background Processes are terminated and SGA is cleared from memory.
• Close the database.
• The database files are closed before the instance is closed.
• You do not need to restore the instance when you open the database again.

2-Transactional :

In this shutdown mode the following steps occur:-

• All users cannot start new transactions.
• The moment the user finishes the current transaction, his connection to the database is disconnected.
• The moment all transactions in the database are finished, the database is closed.
• You do not need to restore the instance when opening the database again.

3- IMMEDIATE:

In this shutdown mode the following steps occur:-

• Current operations in the database are terminated immediately.
• Oracle Server does not wait for current users in the database to terminate their connection.
• Oracle Server performs a rollback of currently active operations in the instance.
• Database files are closed before closing the instance.
• You do not need to perform an instance restore when you open the database again.

4- ABORT: 

In this shutdown mode the following steps occur:-

• Current operations in the database are terminated immediately.
• Current users in the database are not waited for to terminate their connection.
• Data in the buffer is not written to disk.
• Operations that have not been committed are not rolled back.
• The instance is terminated without closing the database files.
• When we open the database again we need to restore the Instance.