In my database, I have table wp_postmeta, example:

| meta_key | meta_value |  post_id   |
---------------------------------
   points  |     12     |  23
   points  |     2      |  18
   lorem   |     ipsum  |  92
   points  |     8      |  15

I want to order table by points and get the row number based on meta_value. Basically a rank system, with highest number at the top.

For example, ordering points by meta_value:

| meta_key | meta_value |  post_id   |
---------------------------------
   points  |     12     |  23
   points  |     8      |  15
   points  |     2      |  18

post_id with value 15 will be rank 2.

What SQL query can I run to achieve this with optimisation in mind?

What I've tried so far

I have achieved this via query:

$query="
    SELECT post_id,FIND_IN_SET(
                  post_id,(SELECT GROUP_CONCAT( post_id ORDER BY meta_value * 1 DESC)
                          FROM $wpdb->postmeta
                          WHERE meta_key ='points')
                       ) AS `rank`
    FROM $wpdb->postmeta
    WHERE meta_key ='points'
    AND post_id = '".$post_id."'
    ";

$result  = $wpdb->get_row($query);

$rank = $result->rank;

Works fine. However, this query is very slow.

How can I make this query faster?