title: How to solve sql problem on matching unrequited?
body: <p>Hi I am a beginner in sql and I have the following problems that I want to know how to solve.</p>
  <p>Below is a list with CA CB, so if value in CA CB appears in CB CA returns true, otherwise returns false.</p>
  <pre><code>CA CB
  6  5 
  5  6 
  2  3 
  3  2 
  4  1 
  </code></pre>
  <p>Results should be like this <br /></p>
  <pre><code>CA CB  
  6  5  True
  5  6  True 
  2  3  True 
  3  2  True 
  4  1  False 
  </code></pre>
  <p>If anyone know how I could write a sql to express it?
  Thanks a lot!</p>