First correct answer! Yay for me 😉

I liked this question - especially the first part about IDENTITY allowing duplicates, which I am sure will surprise many people.

I am less sure about the wording in the second part of the question, "SQL Server does not have an efficient way to retrieve rows based on a known value for PersonID." because that rather depends on the number of rows in the table.

I don't think it would have been giving too much away to say something like "SQL Server cannot use an index to locate rows based on a known value for PersonID".

Paul