PHP uses recursion to generate article trees, _PHP tutorial

function category_tree($fatherid){
  //require_once("mysql_class/config.inc.php");
  //require_once("mysql_class/Database.class.php");
  $db = new Database(DB_SERVER, DB_USER, DB_PASS, DB_DATABASE);
  $db->connect();
  $sql = "SELECT id,title,url FROM ".TABLE_TASK." 
     WHERE fatherid=$fatherid and ispublic=1 order by id asc";
  $articles = $db->query($sql);
  $db->close();
  while ($record = $db->fetch_array($articles)){
    $i = 0;
    if ($i == 0){
      if($fatherid==0){
        echo '<ul class="article-list-no-style border-bottom">';
      }else{
        echo '<ul class="article-list-no-style">';
      }
      
    }
    if($fatherid==0){
      echo '<li><span class="glyphicon glyphicon-log-in" 
      aria-hidden="true" id="han'.$record['id'].'">
      </span>  <a href="'.$record['url'].'" target="_blank">' 
      . $record['title'].'</a>';
    }else{
      echo '<li><span class="glyphicon glyphicon-chevron-right" aria-hidden="true">
      </span> <a href="'.$record['url'].'" target="_blank">' 
      . $record['title'].'</a>';
    }
    
    category_tree($record['id']);
    echo '</li>';
    $i++;
    if ($i > 0){
      echo '</ul>';
    }
  }
}

category_tree(0) //先提取最顶层文章