Joe Celko is very much of a purist when it comes to relational databases. If you have ever tried to adopt the code examples he provides in his books, you'll soon realize that they tend to run very slowly if at all. In his "SQL for Smarties" book he provides several different ways of deriving median values. Some of this code doesn't work at all, while other code runs excruciating slowly (he doesn't approve of the use of cursors, which IMHO is the only practical way of addressing this particular problem).