I've got a user table keyed on an auto-increment int column that looks something like this:
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
Are there any practical performance advantages to using a DESC index (primary key) rather than the default ASC?
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.
Is my understanding correct?