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. 成功回傳TRUE失敗回傳FALSE。
注: This function was introduced in PHP 3.0.13 and requires MySQL 3.23.3 or higher. It is not available in PHP 4.