I would have done what you did; recognise that SQL is such a large product that even the smartest people have gaps in their knowledge and try to explain as briefly as possible that you were confident of your answer.

If they continued to push it I would suggest that perhaps they can research it further after the interview, or we can have a session on it after I've started working with them.

But beyond that, if they're willing to pull out the stops and accuse you of making things up in the interview (it's rare but not unheard of) then be thankful you've just dodged a bullet; who wants to commit the next year or more working for someone who has such poor interpersonal skills.