一个在PHP中利用递归实现论坛分级显示的例子(为了简单起见，我将分页显示部分去掉了)

递归|分页|显示

/*存放帖子的表结构
CREATE TABLE announce (
   announce_id int(11) NOT NULL auto_increment,
   board_id smallint(6) NOT NULL,
   title varchar(100) NOT NULL,
   content tinytext,
   add_time datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
   auth_name varchar(20) NOT NULL,
   auth_mail varchar(40),
   hit_count smallint(6) NOT NULL,
   bytes mediumint(9) NOT NULL,
   parent_id tinyint(4) NOT NULL,
   auth_ip varchar(15) NOT NULL,
   top_id int(11) NOT NULL,
   return_count tinyint(4) NOT NULL,
   face char(3) NOT NULL,
   PRIMARY KEY (announce_id),
   KEY board_id (board_id),
   KEY top_id (top_id)
);
*/

function show_announce($id,$self_id){
    global $dbconnect;
    global $board_id;
    $query="select * from announce where announce_id='$id'";
    $result=mysql_query($query,$dbconnect);
    $myrow=mysql_fetch_array($result);
    mysql_free_result($result);
    echo "

\n";
    echo " ";
    if($self_id!=$id)
        echo "";
    echo $myrow[title];
    if($self_id!=$id)
        echo "";
    echo " - 【".$myrow[auth_name]."】 ".$myrow[add_time]." [id:$myrow][announce_id] 点击：$myrow[hit_count]] ($myrow[bytes] Bytes) ($myrow[return_count])\n";
    $query="select announce_id from announce where parent_id='$id' order by announce_id desc";
    $result=mysql_query($query,$dbconnect);
        echo "

\n";
    while($myrow=mysql_fetch_array($result)){
        show_announce($myrow[announce_id],$self_id);
    }
        echo "

\n";
    mysql_free_result($result);
    echo "

";
}
?>