function getcategories($parent_id = 0) {   $categories = [];    // 递归查询子分类   $result = mysql_query("select * from categories where parent_id = $parent_id");   while ($row = mysql_fetch_assoc($result)) {     $categories[$row['id']] = $row;     $categories[$row['id']]['sub_categories'] = getcategories($row['id']);   }    return $categories; }  $categories = getcategories();

<ul>   <?php foreach ($categories as $category): ?>   <li>     <a href="#"><?php echo $category['name']; ?></a>     <?php if (!empty($category['sub_categories'])): ?>     <ul>       <?php foreach ($category['sub_categories'] as $sub_category): ?>       <li>         <a href="#"><?php echo $sub_category['name']; ?></a>       </li>       <?php endforeach; ?>     </ul>     <?php endif; ?>   </li>   <?php endforeach; ?> </ul>