title: SQL query for something like "not having"?
body: <p>I am trying to write a query that will return what hosts are missing a piece of software:</p>
  
  <pre><code>Host                    Software
  A                       Title1
  A                       Title2
  A                       Title3 
  B                       Title1
  B                       Title3
  C                       Title4
  C                       Title3
  </code></pre>
  
  <p>How to query for which hosts are missing Title2 (should be B and C)? I've tried GROUP BY, HAVING and subquery using COUNT but I don't seem to have the right idea.</p>