DROP USER removes the specified user from the database. It does not remove tables, views, or other objects owned by the user. If the user owns any database, an error is raised.
The message returned if the user is successfully deleted.
This message occurs if the user name is not found.
You must drop the database first or change its ownership.
Use CREATE USER to add new users, and ALTER USER to change a user's attributes. PostgreSQL includes a program dropuser that has the same functionality as this command (in fact, it calls this command) but can be run from the command shell.
The DROP USER statement is a PostgreSQL extension. The SQL standard leaves the definition of users to the implementation.