An interview is a conversation, which is a very high bandwidth medium of information exchange. But in order to get to the level of conversation, both parties need to be speaking the same language. What this test establishes is the baseline level of common language that makes it even possible to have a conversation about SQL databases. Someone who can't handle these sorts of questions is not someone I can usefully have a conversation about SQL with. I can teach them, and sometimes it's useful to have a pedagogical sort of interview; but for a standard, "can you do this job" interview, no, I need to be able to establish a baseline level of common understanding.