Recursive categories with a single query?

Question

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

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.