Not to say that this was not a good article, which it was, it seems we are not covering the killer scalar UDF issue. a scalar function is reasonably fast EXCEPT when you put some type of data access within the function. When this happens it will kill performance. I havent tried your method yet involving that scenario but I will today:) that would be for a calendar function that accesses a calendar table.

When writing a small function that accesses a table to get one value, I find it better to just put the logic of the function directly in the calling select statement and not use a function at all and, even though it is basically the same code, it will run much faster. but then again you would lose the benefits of actually having a function that gives one place to manage the code from.