title: MySQL: difference of two result sets
body: <p>How can I get the set difference of two result sets?</p>
  
  <p>Say I have a result set (just one column in each):</p>
  
  <pre><code>result1:
  'a'
  'b'
  'c'
  
  result2:
  'b'
  'c'
  </code></pre>
  
  <p>I want to minus what is in result1 by result2: result1 - result2 such that it equals:</p>
  
  <pre><code> difference of result1 - result2:
   'a'
  </code></pre>