PHP MySQL code optimize - php

Question

Is there any MySQL function that will optimize this code? A child ID getting all parent ID
function get_parents() {
$ids = array();
while($id) :
$query = "SELECT placement_id FROM referrals WHERE user_id = $id";
$query = $this->db->query($query);
$result = $query->row();
if(!isset($result->placement_id)) :
break;
elseif(isset($result->placement_id) && $result->placement_id == 2) :
break;
endif;
$id = $result->placement_id;
array_push($ids, $id);
if($result) :
continue;
endif;
break;
endwhile;
return $ids;
}
The code above will return all parent ID of given user_id, this will stop if nothing is found. I found this code too slow and heavy load.
My Table
relations table
| id | user_id | placement_id |
| 1 | 2 | NULL |
| 2 | 3 | 2 |
| 3 | 4 | 2 |
| 4 | 5 | 3 |
| 5 | 6 | 4 |
| 6 | 7 | 3 |
| 7 | 8 | 3 |
| 8 | 9 | 3 |
| 9 | 10 | 6 |
| 10 | 11 | 5 |
| 11 | 12 | 6 |
| 12 | 13 | 4 |
| 13 | 14 | 3 |
| 14 | 15 | 9 |
| 15 | 16 | 10 |
user_id is the child and parent is placement_id

Answer 1

You can rewrite you code as:
function get_parents() {
$ids = array();
while($id){
$query = "SELECT placement_id FROM referrals WHERE user_id = $id";
$query = $this->db->query($query);
$result = $query->row();
if(isset($result->placement_id) && $result->placement_id !== 2)
{
$id = $result->placement_id;
array_push($ids, $id);
}
}
return $ids;
}
It excludes some additional function calls such continue,break etc. Also, Make sure you have INT as type of user_id with indexing on this column.

Answer 2

I would personally do something like this:
<?php
define('MAX_NEST_DEPTH', 15);
function get_parent($child_id) {
$child_id = (int) $child_id;
$parents = array();
$counter = 0;
do {
$sql = "SELECT placement_id
FROM referrals
WHERE user_id = {$child_id}";
$query = $this->db->query($query);
$result = $query->row();
$child_id = (int) $result->placement_id;
$parent[] = $child_id;
$counter++;
}
while ($child_id != 0 || $counter == MAX_NEST_DEPTH);
return $parents;
}
You wont get around the query in a loop here, mysql does not support n-level-nested SELECT, otherwise we could just do it in one go.