title: List of questions comparison
body: <p>I have a profile that looks like this:</p>
  
  <pre><code>profile_id | answer_id
  ----------------------
  1                1
  1                4
  1               10
  </code></pre>
  
  <p>I have a table which contains a list of responses by poll respondents with structure like this:</p>
  
  <pre><code>user_id | answer_id
  -------------------
  1            1
  1            9
  2            1
  2            4
  2           10
  3           14
  3           29
  </code></pre>
  
  <p>How do I select a list of users that gave all of the answers in the profile?  In this case only user 2.</p>