How do you know how they affect lookups without knowing how they work? Or are you being modest with your not-understanding of how it works and you really mean to say you don't know the full details of a specific implementation?

I'm posting here in part to get a feel for the "fairness" aspect, so appreciate the feedback. I haven't eliminated anybody over this single question, but do see many interviewees get frustrated with it which may hinder their performance afterwards in the interview. If I were to dig in re: "when to use it and how it affects lookups", that would be good discussion.

If most of your candidates cannot answer the question, but you would still hire them I would drop the question. Knowledge of when to use an index is more valuable than the specific mechanics of how the index is implemented.

When I want to test database knowledge, I usually give the candidate a simple database schema and ask them to write progressively harder SQL queries. Database modeling questions are also good for teasing out the seniority of a candidate as well.

Not all interview questions are about eliminating candidates, you want to rank them as well. If all 5 candidates are roughly equal but one knows much more about databases then they are the one that gets hired.

ugh, this new breed of programmers-but-not-computer-scientists make me shudder