Create a hierarchical structure from an array of objects

I have an SQL query to pull data from database, the result is a multidimensional array of stdClass Objects which looks like this:

Array
(
    [0] => stdClass Object
        (
            [category_id] => 81
            [category_name] => 369-1006-0
            [published] => 1
            [category_parent_id] => 8
            [category_child_id] => 81
        )

    [1] => stdClass Object
        (
            [category_id] => 80
            [category_name] => 369-1007-0
            [published] => 1
            [category_parent_id] => 8
            [category_child_id] => 80
        )

    [2] => stdClass Object
        (
            [category_id] => 82
            [category_name] => 369-1012-0
            [published] => 1
            [category_parent_id] => 8
            [category_child_id] => 82
        )

    [3] => stdClass Object
        (
            [category_id] => 85
            [category_name] => 369-1014-0
            [published] => 1
            [category_parent_id] => 8
            [category_child_id] => 85
        )
[........]
);

until this point I can simple use print_r() to dispatch the information as per request by the API... or echo's while's foreach's .... to display that information for easy reading... but the problem is that I can't group them by ID's ... please allow me...

This array are categories and each category as you have guess it they have sub-categories but the categories and sub-categories are associated using a second table so... [Table 1] has all the information about the categories, and [Table 2] has the association, my query join them together so that I can get a single "virtual table"... and the result I get is that multidimensional nightmare.... the idea is to group them in categories with their sub-categories, now here is the catch ...

as you can see in that array I have [category_parent_id] in each group all of them have a value as 1,2,3,4,5... and this values repeat them self per group... as you can see in this little example... so, every [category_parent_id] with the value of 0 is the main category and the rest are sub-categories

This is how my virtual table Table looks like

[category_id] [category_name] [category_parent_id]
       1          item 1            0
       2          item 2            0
       3          item 3            1
       4          item 4            1
       5          item 5            2
       6          item 6            3
       7          item 7            2
       8          item 8            2

// This is the main idea to group them using the multidimensional array aka nightmare

Item 1
  |_item 3
  |_item 4
Item 2
  |_item 5
  |_item 7
  |_item 8

This are my useless attempts:

Attempt 1
    $cc = 0;
    
    foreach ($results as $obj_key => $cc){
    $cc++
        $catsname =  $obj->category_name;
        $catid = $obj->category_id;
        $subcatid = $obj->category_parent_id;
    
        echo $obj_key .' Name';
            foreach($cc as $key=>$value)
            {
                echo $key . $value . '<br> ';
            }
        echo '<br>';        
    }

Attempt 2
$datasetCount = count($results);
 echo "<h2>How many ccats? $datasetCount </h2>";

$i = 0;
foreach ($results as $categorias) {
    $i++;
    echo "<h2>Categoria $i</h2>";
    
    while (list($key, $value) = each ($categorias)) {
        echo "$key: $value<br />";
    }    
}

I have many more attempts but after my second day and multiple examples it seems that is not possible! which I refuse to believe...

Now, don't think I haven't try other solutions, I have, there is an easy way to do this without the array's I can always add another column to the Table 1 [cat_role] value [sub] : [main] that way I wont even use a second table... but there I am, asking my self, if I don't learn this technique what would happen when the rule is very clear tow or tree tables, one hold the data and the other hold the relations.

Inspired by this, as reference @redreggae:

$tree = array();
$nodes = array();

foreach ($results as $category) {
    $id = $category->category_id;
    $category->children = array();
    $nodes[$id] = $category;

    if ($category->category_parent_id == 0) {
        $tree[$id] = & $nodes[$id];
    }

    foreach ($nodes as $id => & $node) {        
        if (isset($nodes[$node->category_parent_id])) {
            $nodes[$node->category_parent_id]->children[$id] = $node;
        }
    }
}

echo '<pre>'; print_r($tree);