title: Order nested sets by another column (other than lft and rgt)
body: <p>I'm trying to make a comment section for a website (PHP/MySQL) where users can post comments
  or reply to already posted ones. I've learned that this is a bit tricky to do because
  RDBMS such as MySQL aren't really created for storing hierarchical data.
  I've found 4 solutions to my problem (adjacency list, path enumeration, nested sets and closure table) 
  of which I've chosen the nested sets (modified pre-order tree traversal).
  I've managed to make this work for pulling and sorting the root comments and their replies
  but I can't seem to find a way to sort the comments by points (other column) whithout breaking
  the parent>child link.</p>
  
  <p>Imagine a table like this:</p>
  
  <pre><code>+-------------------------------+
  | id | comment | lft | rgt | pts|
  +-------------------------------+
  +-------------------------------+
  | 1  | abc     | 1   | 8   | 3  |
  +-------------------------------+
  | 2  | 123     | 2   | 7   | 1  |
  +-------------------------------+
  | 3  | xyz     | 3   | 4   | 5  |
  +-------------------------------+
  | 4  | www     | 5   | 6   | 4  |
  +-------------------------------+
  | 5  | com     | 9   | 10  | 9  |
  +-------------------------------+
  </code></pre>
  
  <p>If I order this by "lft ASC"
  I get the standard chronological order (oldest to newest):</p>
  
  <pre><code>(1) abc
  --(2) 123
  ----(3) xyz
  ----(4) www
  (5) com
  </code></pre>
  
  <p>If orered by "rgt DESC"
  I get the oposite i.e. new first (newest to oldest):</p>
  
  <pre><code>(5) com
  (1) abc
  --(2) 123
  ----(4) www
  ----(3) wxy
  </code></pre>
  
  <p>All of this works like a charm.
  The problem is I can't seem to find a way to order the comments by points.
  Eventually I would like to get an order like this:</p>
  
  <pre><code>(5) com (9 pts)
  (1) abc (3 pts)
  --(2) 123 (1 pts)
  ----(3) xyz (5 pts)
  ----(4) www (4 pts)
  </code></pre>
  
  <p>Is there any way to make the nested sets model behave like this.
  If possile, the best way to do this is by using the right query, but if such a query doesn't 
  exist ordering them with PHP is also acceptable (if it uses a reasonable ammout of resources).
  And if this isn't reasonably possible using the nested sets model I would like to know
  which model to use to produce all the ways to order the comments mentined above.</p>