我想获得过去x天评论最多的帖子，我有以下代码：

<?php
  global $wpdb;
  $weekstart = date(\'Y-m-d\', strtotime(\'-12 days\'));
  $query = $wpdb->prepare("
  SELECT comment_post_id, count( comment_post_id ) AS c, SUBSTRING( comment_date,1,    5     ) AS d
 FROM        $wpdb->comments
 WHERE       (comment_date >= %s)
 GROUP BY comment_post_id
 ORDER BY c DESC, d DESC ",$weekstart);

 $col_ids = $wpdb->get_col($query);
 if ($col_ids) {
 $postids = implode($col_ids,\', \');
 echo $postids;

function filter_orderby($orderby = \'\') {
global $postids;
$orderby = " FIELD(ID,$postids )";
echo $orderby;
return $orderby;
}

add_filter(\'posts_orderby\', \'filter_orderby\');  
?>

我想按id过滤帖子，问题是回显$orderby（用于测试）会返回以下内容：字段（id，）
而不是实际的顺序，该字段无法识别，并且$PostId为空。我错过了什么？我怎样才能让它正常工作？非常感谢。