title: Select all posts that user hasn't responded to?
body: <p>I have a website that shows posts, and a user can vote on it. After they vote once I don't want it to show to that user again. So I need to have a query that polls all posts and returns the ones the user has not yet responded to.</p>
  
  <p>I was thinking it would be simplest to have a posts table, responses table, and user table. The response table could include a postId, and userId. This could allow me to see all the posts that a user <em>has</em> responded to, but I couldn't figure out how to flip it to show the negation. Also it seems like it would be pretty slow to do it that way.</p>