inner join Vs scalar Function

Question

Which of the following query is better... This is just an example, there are numerous situations, where I want the user name to be displayed instead of UserID

Answer 1

A good question and great to be thinking about SQL performance, etc.

From a pure SQL point of view the first is better. In the first statement it is able to do everything in a single batch command with a join. In the second, for each row in trn_misc_email it is having to run a separate BATCH select to get the user name. This could cause a performance issue now, or in the future

It is also eaiser to read for anyone else coming onto the project as they can see what is happening. If you had the second one, you've then got to go and look in the function (I'm guessing that's what it is) to find out what that is doing.

So in reality two reasons to use the first reason.