title: Find duplicate symmetric rows in a table
body: <p>I have a table which contains data as</p>
  
  <pre><code>col1  col2  
  a      b  
  b      a  
  c      d
  d      c
  a      d 
  a      c
  </code></pre>
  
  <p>For me row 1 and row 2 are duplicate because <code>a, b</code> &amp; <code>b, a</code> are the same. The same stands for row 3 and row 4.</p>
  
  <p>I need an SQL (not PL/SQL) query which gives output as</p>
  
  <pre><code>col1   col2
  a       b
  c       d
  a       d
  a       c
  </code></pre>