PHP-MySQL takes a Long Time to Run

[Senator Mike]

I just finished an application using hierarchical table in mysql DB for a network business.One of my main function that helps determine node depth is displayed below

<?php
##function to determine the depth of a node
function node_depth($netm_id) {
$depth ="SELECT node.netm_id, (COUNT(parent.netm_id) - (sub_tree.depth + 1)) AS depth
FROM tree AS node,
tree AS parent,
tree AS sub_parent,
(
SELECT node.netm_id, (COUNT(parent.netm_id) - 1) AS depth
FROM tree AS node,
tree AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
AND node.netm_id = '".$netm_id."'
GROUP BY node.netm_id
ORDER BY node.lft
)AS sub_tree
WHERE node.lft BETWEEN parent.lft AND parent.rgt
AND node.lft BETWEEN sub_parent.lft AND sub_parent.rgt
AND sub_parent.netm_id = sub_tree.netm_id
GROUP BY node.netm_id
ORDER BY depth ASC";
return $depth;
}
?>

which will return the tree depth of the node passed to the function. However, my problem is that for example when i want to read through the entire network tree to do e.g bonus calculations....it takes a lot of time (because i think the system has to go through the above function to for every tree node). At 200-300 records, the system is using close to 5-7 mins..

What do i do?