php recursive function not working correctly - php

Question

i have a categories table
(id=1 , name=Hand made, parent=0)
(id=2 , name=Factory made, parent=0)
(id=3 , name=chairs, parent=1)
(id=4 , name=tabels, parent=1)
(id=5 , name=old chairs, parent=3)
at the menu if visitor clicked on category OLD CHAIRS , will go to page
products.php?category_id = 5
then at this page i need to know what is the main category_id , which should be HAND MADE with category_id=1
so at this page i want to say
if isset($_REQUEST['category_id']){
do the function till find the main parent,
$mainparentid = main parent category_id
}else { $mainparentid = '';
} echo $mainparentid;
here is my PHP Code
if (isset($_REQUEST['category_id'])) {
function getParent($id) {
global $connection;
$query_rsCategoryId = "SELECT * FROM categories
WHERE category_id = '".$_REQUEST['category_id']."'";
$rsCategoryId = mysql_query($query_rsCategoryId, $connection);
$row_rsCategoryId = mysql_fetch_assoc($rsCategoryId);
$parent = $row_rsCategoryId['category_parent'];
if (mysql_num_rows($rsCategoryId) < 1) {
// Error handling, entry with id $id not found
return null;
}
if ($parent == 0) {
return $id;
} else {
return getParent($parent);
}
}
$mainparentid = getParent($id);
}else {
$mainparentid ='none';
}
echo $mainparentid ;

Answer 1

You always input ID of the category from $_REQUEST. Change line:
WHERE category_id = '".$_REQUEST['category_id']."'";
to:
WHERE category_id = '".$id."'";

Answer 2

You are using parent id from request instead of given via function parameter
// notice $id instead of $_REQUEST['category_id']
$query_rsCategoryId = "SELECT * FROM categories WHERE category_id = '{$id}'";