Oracle DROP USER

Summary: in this tutorial, you will learn how to use the Oracle DROP USER to delete a user from the database.

Introduction to Oracle DROP USER statement

The DROP USER statement allows you to delete a user from the Oracle Database. If the user has schema objects, the DROP USER statement also can remove all the user’s schema objects along with the user.

The following illustrates the basic syntax of the DROP USER statement:

DROP USER username [CASCADE];

In this syntax, you need to specify the user that you want to drop after the DROP USER keywords.

If the user whose schemas contain objects such as views and tables, you need to delete all schema objects of the user first and then drop the user.

Deleting all schema objects of the users first before removing the user is quite tedious. Therefore, Oracle provides you with the CASCADE option.

If you specify the CASCADE option, Oracle will remove all schema objects of the user before deleting the user.

If the schema objects of the dropped user are referenced by objects in other schemas, Oracle will invalidate these objects after deleting the user.

If a table of the dropped user is referenced by materialized views in other schemas, Oracle will not drop these materialized views. However, the materialized views can no longer be refreshed because the base table doesn’t exist anymore.

Note that Oracle does not drop roles created by the user even after it deletes the user.

Notice that if you attempt to delete the user SYS or SYSTEM, your database will corrupt.

Oracle DROP USER statement examples

Let’s take some examples of removing a user from the database.

1) Using Oracle DROP USER to remove a user that has no schema object

First, log in to the Oracle database using the user ot using SQL*Plus:

Enter user-name: ot@pdborcl
Enter password: <user_password>

Second, create a new user called foo:

CREATE USER foo IDENTIFIED BY abcd1234;

Third, drop the user foo using the DROP USER statement:

DROP USER foo;

You should see the following message:

User dropped.

Because the user foo has no schema objects, you could delete it without specifying the CASCADE option.

2) Using Oracle DROP USER to delete a user that has schema objects

First, create a new user called bar and grant the CREATE SESSION and CREATE TABLE system privileges to the user:

CREATE USER bar 
    IDENTIFIED BY abcd1234 
    QUOTA 5m ON users;

GRANT 
    CREATE SESSION,
    CREATE TABLE
TO bar;

Second, use the user bar to log in to the Oracle database:

Enter user-name: bar@pdborcl
Enter password: <bar_password>

Third, create a new table named t1 in the bar user’s schema:

CREATE TABLE t1(
    id NUMBER PRIMARY KEY,
    v VARCHAR2(100) NOT NULL
);

INSERT INTO t1(id,v) 
VALUES(1,'A');

Fourth, go back to the session of the user ot and drop user bar:

DROP USER bar;

Oracle issued the following error:

ORA-01940: cannot drop a user that is currently connected

Fifth, end the user bar’s session first using the exit command:

exit

And issue the DROP USER statement again in the user ot session:

DROP USER bar;

Oracle issued the following message:

ORA-01922: CASCADE must be specified to drop 'BAR'

You could not delete the user bar without specifying CASCADE because the user bar has the table t1 as a schema object.

Seventh, use the DROP USER statement with CASCADE option to delete the user bar:

DROP USER bar CASCADE;

Oracle could delete the user bar and also the table t1.

In this tutorial, you have learned how to use the Oracle DROP USER statement to delete a user and optionally remove all objects in the user’s schema from the Oracle database.

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