我有以下SQL脚本：

$query = $wpdb->prepare(
    "SELECT user_login FROM wpdb->staff as staff
      join wpdb->users as users on staff.wp_user_id  = users.ID
       where full_name =%s",
    $usernametest
);
$userlogin = $wpdb->query( $query );

您的SQL语法有错误；检查与您的MariaDB服务器版本相对应的手册，以了解使用near“->ab\\U staff as staff join wpdb->users as users on staff的正确语法。wp\\u user\\u id=用户。”在第1行