mysql_change_user() changes the logged in user of the current active connection, or the connection given by the optional link_identifier parameter. If a database is specified, this will be the current database after the user has been changed. If the new user and password authorization fails, the current connected user stays active. Возвращает TRUE в случае успешного завершения, FALSE в случае возникновения ошибки.
Замечание: This function was introduced in PHP 3.0.13 and requires MySQL 3.23.3 or higher. It is not available in PHP 4.