T-SQL Functions and Procedures

Function. What’s the point?  

I’ve lost count how many times I have been asked to optimise a poorly performing database and found the culprit to be a function. Now it makes perfect sense to me to program in a way that allows reuse of code. However for some reason calling a function in a Select statement over any large dataset often kills performance. The thing to do here is to re-factor your code taking the offending function out and replace it with in line SQL or better still re-factor to take the sub query out of the statement altogether.