Sort query with parents and childs (by category) in PHP

I have a SQLite DB with a table called "library" containing 3 fields (12php sMb)

Id (unique identifier) // libraryName, containing a string // parentLibId, containing the ID of the parent Library.

If the library is in the "root", parentLibId is Null (empty)

I need an array that will return a tree with parents and child starting from t开发者_运维问答he root.

Anyone know how to do that without too many code?

$dbh = new PDO('sqlite:my.sqlite') or die("Error 0xDB0001");
$sth = $dbh->prepare("SELECT * FROM library");
$sth->execute();
$result = $sth->fetchAll();

I have a time processing page limit given by my friend as a little competition and this part I cannot figure it out, I used a code but it's so long, I feel stupid XD

Any help is welcomed, if I'm unclear, just say it and I'll give more details.

Thank you very much your help is appreciated!!

Have a good evening all!

---

this function is not tested. This is main idea.

getTree();

function getTree($child = null)
{
    $dbh = new PDO('sqlite:my.sqlite') or die("Error 0xDB0001");

    //It's just example. Security and best practice is your problem :p
    if ($child)
        $where = 'parentLibId = ' . $child;
    else
        $where = 'parentLibId IS NULL ';

    $sth = $dbh->prepare("SELECT * FROM library" . $where);
    $sth->execute();

    if ($child)
    {
        $result = $sth->fetchAll()
        $return = $result;
    }else{ //get parents
        while ($result = $sth->fetch())
        {
            //one by one
            $return[] = array(  'parent' => $result, //parent info
                                'childs' => getTree($result['id']) //childs
                            );
        }
    }

    return $return;
}