title: SQL Index Performance - ASC vs DESC
body: <p>I've got a user table keyed on an auto-increment int column that looks something like this: </p>
  
  <pre><code>CREATE TABLE `user_def` (
    `user_id` int(11) NOT NULL AUTO_INCREMENT,
    `user_name` varchar(20) NOT NULL,
    `date_created` datetime NOT NULL,
    PRIMARY KEY (`user_id`),
    UNIQUE KEY `user_name_UNIQUE` (`user_name`),
  ) ENGINE=MyISAM
  </code></pre>
  
  <p>Are there any practical performance advantages to using a DESC index (primary key) rather than the default ASC?</p>
  
  <p>My suspicion / reasoning is as follows:
  I'm assuming that more recent users are going to be more active (i.e. accessing the table more often), therefore making the index more efficient.</p>
  
  <p>Is my understanding correct?</p>