Wordpress的错误值为Wordpress

Question

$myEvents = $wpdb->prefix . 'Events';

       $sql = "SELECT COALESCE(max(event_id),0) FROM $myEvents WHERE event_title = 'pd'";
        $numb = $wpdb->get_results($sql);
        $num = $numb->{'event_id'};
        echo $num;

以下代码始终回显0，即使我知道它不应该。怎么了？