title: SQL to remove specific rows from select
body: <p>Ive got a table:</p>
  
  <pre><code>UserA UserB UserBB UserAA
  </code></pre>
  
  <p>for example:</p>
  
  <pre><code>1 2 2 1
  1 3 3 1
  2 1 1 2
  2 4 4 2
  2 5 5 2
  5 2 2 5
  </code></pre>
  
  <p>What I want to achieve is to remove rows (duplicates) like to only leave rows as in example:</p>
  
  <pre><code>1 2 2 1
  1 3 3 1
  2 4 4 2
  2 5 5 2
  
  
  
  2 1 1 2 -&gt; deleted because there is already 1 2 2 1 
  5 2 2 5 -&gt; deleted because there is already 2 5 5 2
  </code></pre>
  
  <p>How to write such a query ?</p>
  
  <p>Thanks for help</p>