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    <h2>Proposed Solution</h2> <p>This following example gives a little more than you ask for, but it's a really nice way of doing it and still demonstrates where the information comes from at each stage.</p> <p>It uses the following table structure:</p> <pre><code>+--------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------+------------------+------+-----+---------+----------------+ | id | int(10) unsigned | NO | PRI | NULL | auto_increment | | parent | int(10) unsigned | NO | | NULL | | | name | varchar(45) | NO | | NULL | | +--------+------------------+------+-----+---------+----------------+ </code></pre> <p>Here it is:</p> <pre><code>&lt;?php // Connect to the database mysql_connect('localhost', 'root', ''); mysql_select_db('test'); echo '&lt;pre&gt;'; $categories = Category::getTopCategories(); print_r($categories); echo '&lt;/pre&gt;'; class Category { /** * The information stored in the database for each category */ public $id; public $parent; public $name; // The child categories public $children; public function __construct() { // Get the child categories when we get this category $this-&gt;getChildCategories(); } /** * Get the child categories * @return array */ public function getChildCategories() { if ($this-&gt;children) { return $this-&gt;children; } return $this-&gt;children = self::getCategories("parent = {$this-&gt;id}"); } //////////////////////////////////////////////////////////////////////////// /** * The top-level categories (i.e. no parent) * @return array */ public static function getTopCategories() { return self::getCategories('parent = 0'); } /** * Get categories from the database. * @param string $where Conditions for the returned rows to meet * @return array */ public static function getCategories($where = '') { if ($where) $where = " WHERE $where"; $result = mysql_query("SELECT * FROM categories$where"); $categories = array(); while ($category = mysql_fetch_object($result, 'Category')) $categories[] = $category; mysql_free_result($result); return $categories; } } </code></pre> <h2>Test Case</h2> <p>In my database I have the following rows:</p> <pre><code>+----+--------+-----------------+ | id | parent | name | +----+--------+-----------------+ | 1 | 0 | First Top | | 2 | 0 | Second Top | | 3 | 0 | Third Top | | 4 | 1 | First Child | | 5 | 1 | Second Child | | 6 | 2 | Third Child | | 7 | 2 | Fourth Child | | 8 | 4 | First Subchild | | 9 | 4 | Second Subchild | +----+--------+-----------------+ </code></pre> <p>And thus the script outputs the following (lengthy) information:</p> <pre><code>Array ( [0] =&gt; Category Object ( [id] =&gt; 1 [parent] =&gt; 0 [name] =&gt; First Top [children] =&gt; Array ( [0] =&gt; Category Object ( [id] =&gt; 4 [parent] =&gt; 1 [name] =&gt; First Child [children] =&gt; Array ( [0] =&gt; Category Object ( [id] =&gt; 8 [parent] =&gt; 4 [name] =&gt; First Subchild [children] =&gt; Array ( ) ) [1] =&gt; Category Object ( [id] =&gt; 9 [parent] =&gt; 4 [name] =&gt; Second Subchild [children] =&gt; Array ( ) ) ) ) [1] =&gt; Category Object ( [id] =&gt; 5 [parent] =&gt; 1 [name] =&gt; Second Child [children] =&gt; Array ( ) ) ) ) [1] =&gt; Category Object ( [id] =&gt; 2 [parent] =&gt; 0 [name] =&gt; Second Top [children] =&gt; Array ( [0] =&gt; Category Object ( [id] =&gt; 6 [parent] =&gt; 2 [name] =&gt; Third Child [children] =&gt; Array ( ) ) [1] =&gt; Category Object ( [id] =&gt; 7 [parent] =&gt; 2 [name] =&gt; Fourth Child [children] =&gt; Array ( ) ) ) ) [2] =&gt; Category Object ( [id] =&gt; 3 [parent] =&gt; 0 [name] =&gt; Third Top [children] =&gt; Array ( ) ) ) </code></pre> <h2>Example Usage</h2> <p>I'd suggest creating some kind of recursive function if you're going to create menus from the data:</p> <pre><code>function outputCategories($categories, $startingLevel = 0) { $indent = str_repeat(" ", $startingLevel); foreach ($categories as $category) { echo "$indent{$category-&gt;name}\n"; if (count($category-&gt;children) &gt; 0) outputCategories($category-&gt;children, $startingLevel+1); } } $categories = Category::getTopCategories(); outputCategories($categories); </code></pre> <p>which would output the following:</p> <pre><code>First Top First Child First Subchild Second Subchild Second Child Second Top Third Child Fourth Child Third Top </code></pre> <p><em>Enjoy</em></p>
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