Estrarre categorie e sottocategorie

[k.b]

Con questa versione alternativa fai una sola query ed elabori i dati in PHP (limitare il numero di query da' grossi vantaggi in termini di prestazioni):

<?php
$sql = 'SELECT id, parent, name
        FROM tree';

$result = mysql_query($sql);

$data = array();

while ( $row = mysql_fetch_object($result) ) {
    if ( $row->parent == 0 ) {
        $root = $row->id;
    } else {
        $data[$row->parent][$row->id] = $row->name;
    }
}

function build_tree($main, $root) {
    $current = array();
    foreach ( $main[$root] as $id => $name ) {
        if ( isset($main[$id]) ) {
            $current[$id] = array(
                'name' => $name,
                'children' => build_tree($main, $id),
            );
        } else {
            $current[$id] = array(
                'name' => $name,
            );
        }
    }
    return $current;
}

function print_tree($tree) {
    echo "<ul>";
    foreach ( $tree as $branch ) {
        echo "[*]{$branch['name']}\n";
        if ( !empty($branch['children']) ) {
            print_tree($branch['children']);
        }
    }
    echo "[/list]\n";
}

$tree = build_tree($data, $root);

print_tree($tree);