看来，切换到博客可能太不可预测，无法用于主要网站设计。这是我第一次尝试基于SQL的解决方案。

function get_intro_post($blogid, $thumb_size=\'\') {

  global $wpdb, $post;

  // Get the system defined table prefix
  $prefix = $wpdb->prefix;

  // Create a full table prefix by combining the system prefix with the blogid
  $tbl = $prefix . $blogid;

  // First query selects posts with the \'Introduction\' category
  $sql = "SELECT `ID` FROM {$tbl}_posts as p";
  $sql .= " JOIN {$tbl}_term_relationships tr ON p.ID = tr.object_id";
  $sql .= " JOIN {$tbl}_terms t ON tr.term_taxonomy_id = t.term_id";
  $sql .= " WHERE t.name = \'Introduction\'";

  // Only want/expect one result row, so use get_row()
  $intro = $wpdb->get_row($sql);
  $postid = $intro->ID;

  // Second query joins the postmeta table to itself so that I can find
  // the row whose post_id matches the _thumbnail_id, found in meta_value, 
  // for the post whose post_id matches the one I found in the previous query.
  $sql = "SELECT p2.meta_key, p2.meta_value FROM  `{$tbl}_postmeta` p1";
  $sql .=   " JOIN  `{$tbl}_postmeta` p2 ON p1.meta_value = p2.post_id";
  $sql .=   " WHERE p1.meta_key =  \'_thumbnail_id\'";
  $sql .=   " AND p1.post_id =  \'{$postid}\'";
  $sql .=   " LIMIT 0 , 30";

  // Expecting 2 result rows, so use get_results()
  $thumb_meta = $wpdb->get_results($sql);

  // Set $src to FALSE as the default
  $src = FALSE;

  // Make sure the query returned results
  if(!empty($thumb_meta)) {
    foreach($thumb_meta as $row) {
        // We just want to find the row where meta_key is the attached file
        // and then set our $src var to that value, which is the image path
        if ($row->meta_key == "_wp_attached_file") $src = $row->meta_value;
    }
  }

  // If we found an image path above, I\'ll append the rest of the path to the front
  if($src) { $src = "/wp-content/blogs.dir/{$blogid}/files/{$src}"; }

  // Handy core function to grab the blogname of another network\'s blog, by ID
  $blogname = get_blog_details( $blogid )->blogname;

  // Make an associative array holding the elements we need, 
  // some pulled from the global $post context
  $p = array(
    \'title\' => get_the_title(),
    \'content\' => get_the_content(),
    \'excerpt\' => get_the_excerpt(),
    \'permalink\' => get_permalink(),
    \'blogname\' => $blogname,
    \'thumbnail\' => $src
  );

  // Return an object with the post details mentioned above
  return (object) $p;
}