DROP USER removes the specified user. It does not remove tables, views, or other objects owned by the user. If the user owns any database, an error is raised.
Message returned if the user was successfully deleted.
Message returned if the specified user does not exist.
You must drop the database first or change its ownership.
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.