Category Tree

category_tree.php

<?php

$nodeList = array();
$tree = array();

$query = mysql_query("SELECT category_id, name, parent FROM categories ORDER BY parent");
while ($row = mysql_fetch_assoc($query)){
    $nodeList[$row['category_id']] = array_merge($row, array('children' => array()));
}
mysql_free_result($query);

foreach ($nodeList as $nodeId => &$node) {
    if (!$node['parent'] || !array_key_exists($node['parent'], $nodeList)) {
        $tree[] = &$node;
    } else {
        $nodeList[$node['parent']]['children'][] = &$node;
    }
}

unset($node);
unset($nodeList);