title: How to select all users for which given parameters are always true
body: <p>I have a table containing users and locations where they were seen:</p>
  
  <pre><code>user_id  | latitude | longitude | date_seen
  -------------------------------------------
  1035     | NULL     | NULL      | April 25 2010
  1035     | 127      | 35        | April 28 2010
  1038     | 127      | 35        | April 30 2010
  1037     | NULL     | NULL      | May 1 2010
  1038     | 126      | 34        | May 21 2010
  1037     | NULL     | NULL      | May 24 2010
  </code></pre>
  
  <p>The dates are regular timestamps in the database; I just simplified them here.</p>
  
  <p>I need to get a list of the users for whom latitude and longitude are always null. So in the above example, that would be user 1037--user 1035 has one row with lat/lon information, and 1038 has two rows with lat/lon information, whereas for user 1037, in both rows the information is null.</p>
  
  <p>What query can I use to achieve this result?</p>