There has always been a lot of confusion in terms of performance between correlated sub-queries vs user-defined functions. So, I've taken it upon myself to try to figure out which one is more effecient. The results I have found are by no means conclusive, but will hopefully give you an idea as to when to use which approach as well as a general methodology for how to compare queries for effeciency purposes. First, I'll start by creating a scalar user defined function that accepts the EmployeeID...