When someone can’t answer an interview question about relational databases, it might be that they don’t know anything about relational databases. I thought you all were better than this. Why are you asking questions about relational databases? Why not just have candidates accomplish the thing you're assessing with an actual relational database ? I know you're work-sample-literate! But if your feedback emphasizes comm…
Also the next few lines kinda address what you are saying:
> It also might be that they know them inside-and-out but aren’t used to answering questions on the fly, or that our question didn’t use the vocabulary they’re familiar with, or that they misheard the question and answered a different one. It made quite a difference just to phrase the feedback in a way which acknowledged all those possibilities.