how to get the hierarchical menu from mysql

Question

I have a table having hierarchical menus like

"id" "parent_id" "name"
1 0 menu
2 1 item1
3 2 item1_1
4 1 item2
5 4 item2_1
...
...

and I have 100s of menu items here. In order to get all items in an array I have to write a recursive function like this

getmenu function(parent_id = 1)
{
  $items = mysql_query("SELECT id FROM table WHERE parent_id = " + parent_id);
  while ($item = msyql_Fetch_assoc($items)) {
    ...here I put them in array and call recursive function again to get sub items...
    getmenu($item['id']);
  }   
}

but this executes 100s of queries. Is this the best way to do this, to get hierarchical menus from database? Does this way loads mysql much?

Answer 1

$stmt = "SELECT id, parent_id FROM table";
$items = Array();
$result = mysql_query($stmt);

while ($line = mysql_fetch_assoc($result)) {
    $items[] = $line;
}

$hierarchy = Array();

foreach($items as $item) {
    $parentID = empty($item['parent_id']) ? 0 : $item['parent_id'];

    if(!isset($hierarchy[$parentID])) {
        $hierarchy[$parentID] = Array();
    }

    $hierarchy[$parentID][] = $item;
}

The root level will be $hierarchy[0]. Keys are items ids and values are all direct children.

Answer 2

Take a look at Nested Sets if you don't mind a little more complex solution. Nested Sets have a very good SELECT performance and I assume that selecting is more important here.

With the help of Nested Sets, complex hierarchical data can be managed in a very fashionable and elegant way.