title: Delete records not present in join
body: <p>Imagine two tables (A and B):</p>
  
  <pre><code>A        B
  1        2
  2        3 
  6        5 
  4        7
  9        11
           13
           23
           9 
  </code></pre>
  
  <p>Now I want to delete records from A that are not present in B, e.g deleting 1, 6 and 4 from A. </p>
  
  <p>My initial idea is that you could 'negate' the results of a join.</p>