> has somewhat unpredictable behavior on complex queries. Including counts. By default, MyISAM compresses its primary key: http://www.mysqlperformanceblog.com/

> has somewhat unpredictable behavior on complex queries. Including counts. By default, MyISAM compresses its primary key: http://www.mysqlperformanceblog.com/2006/05/13/to-pack-or-not-to-pack-myisam-key-compression/ http://www.mysqlperformanceblog.com/2006/05/13/to-pack-or-no... So you get bad performance when the primary key is accessed in descending order: http://bugs.mysql.com/bug.php?id=17847 http://bugs.mysql.com/bug.php?id=17847 If this corrupted, you get a different row count when you order by ascending or descending key. I've seen this in the wild. Unfortunately, this possibility has been repeatedly missed by developers: http://bugs.mysql.com/bug.php?id=28542 http://bugs.mysql.com/bug.php?id=28542 http://bugs.mysql.com/bug.php?id=28658 http://bugs.mysql.com/bug.php?id=28658 http://bugs.mysql.com/bug.php?id=35605 http://bugs.mysql.com/bug.php?id=35605 MySQL is a nice bit bucket but I'll continue using Postgres for anything important.