CREATE TABLE categories (
cid int(10) unsigned NOT NULL auto_increment,
title varchar(128) NOT NULL default ,
cleft int(10) unsigned NOT NULL default 0,
cright int(10) unsigned NOT NULL default 0,
clevel int(10) unsigned NOT NULL default 0,
PRIMARY KEY (cid),
KEY cleft (cleft, cright, clevel)
) TYPE=MyISAM;

<?
/*
   Работа с деревом по алгоритму Nested Sets.
   Подготовка таблицы к работе.
   Используется класс dbtree.php
   Взять его можно: http://dev.e-taller.net/dbtree/

    ---------------------
    Author: Maxim Matykhin.
    mailto: max@webscript.ru
*/

$table=categories; // таблица категорий
$id_name=cid;     // имя поля первичного ключа
$field_names = array( // имена полей таблицы
   left => cleft,
   right=> cright,
   level=> clevel,
);

require_once cd.php;
require_once dbtree.php;

$dbh=new CDataBase(dbname, localhost, root, password);
$Tree = new CDBTree($dbh, $table, $id_name, $field_names);
// создаем корневую запись (см. пояснения к статье)
$id=$Tree->clear(array(title=>Каталог ресурсов));

$level_2=array();
$level_2[0]=$Tree->insert($id,array(title=>Программирование));
$level_2[1]=$Tree->insert($id,array(title=>Новости));
$level_2[2]=$Tree->insert($id,array(title=>Сопрт));
$level_2[3]=$Tree->insert($id,array(title=>Разное));

// теперь создадим несколько записей третьего уровня
$level_3=array();
$level_3[0]=$Tree->insert($level_2[0],array(title=>PHP));
$level_3[1]=$Tree->insert($level_2[0],array(title=>Perl));
$level_3[2]=$Tree->insert($level_2[0],array(title=>Delphi));

$level_3[3]=$Tree->insert($level_2[1],array(title=>Криминал));

$level_3[4]=$Tree->insert($level_2[2],array(title=>Футбол));
$level_3[5]=$Tree->insert($level_2[2],array(title=>Шахматы));

$level_3[6]=$Tree->insert($level_2[3],array(title=>Медицина));
$level_3[7]=$Tree->insert($level_2[3],array(title=>Экология));
$level_3[8]=$Tree->insert($level_2[3],array(title=>Промышленность));
                                             
// и для некоторых сделаем четвертый уровень
$Tree->insert($level_3[0],array(title=>PEAR));
$Tree->insert($level_3[8],array(title=>Металлургия));
$Tree->insert($level_3[6],array(title=>Морги));
echo Таблица заполнена.;
?>

<? $id=$Tree->clear(array(title=>Каталог ресурсов)); ?>

<?
$query=SELECT * FROM .$table. ORDER BY cleft ASC;
$result=$dbh->query($query);
while($row = $dbh->fetch_array($result))
{
   echo str_repeat(&nbsp;,6*$row[clevel]).$row[title].<br>;
}
?>

SELECT
cid,
title,
clevel
FROM
categories
WHERE
cleft BETWEEN $cleft AND $cright
ORDER BY cleft

SELECT
cid,
title,
clevel
FROM
categories
WHERE
cleft BETWEEN $cleft AND $cright AND
clevel = $clevel+1
ORDER BY cleft

SELECT
cid,
title,
clevel
FROM
categories
WHERE
cleft < $cleft AND
cright > $cright
ORDER BY cleft

CREATE TABLE categories (
cat_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
cat_left INT UNSIGNED NOT NULL,
cat_right INT UNSIGNED NOT NULL,
cat_level INT UNSIGNED NOT NULL,
PRIMARY KEY(cat_id)
KEY (cat_left, cat_right, cat_level)
);

OpenPGP Message Format

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Session Traversal Utilities for NAT (STUN)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Explicit Multicast (Xcast) Concepts and Options

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.