SQL Efficiency: WHERE IN Subquery vs. JOIN then GROUP

Question

As an example, I want to get the list of all items with certain tags applied to them. I could do either of the following:

SELECT Item.ID, Item.Name
FROM Item
WH         


        

Answer 1

It's pretty much impossible (unless you're one of those crazy guru DBAs) to tell what will be fast and what won't without looking at the execution plan and/or running some stress tests.