Recursive categories with a single query?

Question

Hi there, I have a website with articles and sections, each sections can have a parent section, as much as they like for example:

subject 1
 -subject 2 
 --subject 3
 -subject 4
 --subject 5
 --subject 6
 ---subject 7
subject 8
subject 9

etc..

Now, i want to fetch them recursively, what is the most efficient way to do it via php and mysql?

Tnx in advanced.

Answer 1

That depends on how you have stored your data. There is a good article on MySQL.com called Managing Hierarchical Data in MySQL that talks about this.

Answer 2

the first part of the article relates only to 4 levels, the last part is not the way I want to do it.

my structure is something like that:

+-------------+----------------------+--------+
| category_id | name                 | parent |
+-------------+----------------------+--------+
|           1 | test                 |   NULL |
|           2 | subject1             |   1    |
|           3 | subject2             |   1    |
|           4 | subject3             |   2    |
|           5 | subject4             |   4    |
+-------------+----------------------+--------+

I dont want to complicate things, I want to do it in the most simple way, but to fetch the data in the most efficient way.

Answer 3

if assume, that your table has id, id_parrent and name fields

function tree($id)
{
    $query = "SELECT `name`,`id` from `table` WHERE `id_parrent` = '$id'";
    $result = mysql_query($query);
     if(mysql_num_rows($result) != 0)
       {
            echo "<ul>";
            while($row = mysql_fetch_array($result))
            {             
                 echo "<li>",$row[name],"</li>";
                 tree($row[id]);
            }
            echo "</ul>";
       }
}

by so you'll get the whole tree

category1
       category1_1
       category1_2
              category1_2_1
              category1_2_2
       category1_3
...........................

Answer 4

Well, you can fetch all the categories in an array in just the one query, as you know:

$query = "SELECT `name`,`id` from `table`";

Having that in an array, you can build the tree with some nested loops. It won't be fast, but is simple, and faster than using recursive queries. Also, you can cache the built tree and not having to rebuild it every time.

Answer 5

I cant guarentee I havent made any syntax mistakes but this should work with one query.

class menuSystem{ 
var $menu;
var $db; #this variable is my db class assigned from the construct, I havent written the construct in, I can if you need it
function startNav(){
    $this->db->runQuery("select * from table order by parent asc");
    $menu = array(0 => array('children' => array()));
    while ($data = $this->db->fetchArray()) {
      $menu[$data['category_id']] = $data;
      $menu[(is_null($data['parent']) ? '0' : $data['parent'] )]['children'][] = $data['category_id'];
    }
    $this->menu = $menu;
    $nav = '<ul>';
    foreach($menu[0]['children'] as $child_id) {
      $nav .= $this->makeNav($menu[$child_id]);
    }
    $nav .= '</ul>';
}

function makeNav($menu){
   $nav_one = '<li>'."\n\t".'<a href="#">'$menu['name'].'</a>';
    if(isset($menu['children']) && !empty($menu['children'])) {
      $nav_one .= "<ul>\n";
      foreach($menu['children'] as $child_id) {
        $nav_one .= $this->makeNav($this->menu[$child_id]);
      }
      $nav_one .= "</ul>\n";
    }
    $nav_one .= "</li>\n";
return $nav_one;
}

}

EDIT: sorry I use this in my code as a class and thought I had managed to take it out of a class for you but forgot I needed $this->menu

UPDATE: I think the below is out of a class now, sorry for such a long answer

$result = mysql_query("select * from table order by parent_id asc");
$menu = array(0 => array('children' => array()));
while ($data = mysql_fetch_array($result)) {
  $menu[$data['category_id']] = $data;
  $menu[(is_null($data['parent_id']) ? '0' : $data['parent_id'] )]['children'][] = $data['category_id'];
}
$global_menu = $menu;
$nav = '<ul>';
foreach($menu[0]['children'] as $child_id) {
  $nav .= makeNav($menu[$child_id]);
}
$nav .= '</ul>';

function makeNav($menu) {
  global $global_menu;
  $nav_one = '<li>'."\n\t".'<a href="#">' . $menu['name'].'</a>';
  if(isset($menu['children']) && !empty($menu['children'])) {
    $nav_one .= "<ul>\n";
    foreach($menu['children'] as $child_id) {
      $nav_one .= makeNav($global_menu[$child_id]);
    }
    $nav_one .= "</ul>\n";
  }
  $nav_one .= "</li>\n";
  return $nav_one;
}

Hope it helps

Luke

Answer 6

You could have a look at this topic : how to get the hierarchical menu from mysql that was opened yesterday and is about the same thing.

Answer 7

If the tree isn't too large, you can simply build the tree in PHP using some clever references.

$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);

This will give you the tree structure in $tree with the children in the respective children-slot.

We've done this with fairly large trees ( >> 1000 items) and it's very stable and a lot faster than doing recursive queries in MySQL.

Answer 8

From your example to each category save its full path in another field:
1 - 1
2 - 1.2
3 - 1.2.3
4 - 1.4
5 - 1.4.5
6 - 1.4.6
7 - 1.4.6.7
8 - 8
9 - 9

and then just query with ORDER BY on that field

Answer 9

I have a good solution for this problem.

It does not use recursion. And it requires a single query to the database.

I have just posted the code in my answer to a similar question here:

http://stackoverflow.com/questions/2871861#3368622

Thanks.