title: Delete duplicate in sql based on other column value
body: <p>I want to remove duplicates based on below condition.</p>
  
  <p>My table contains data like cross relation. Column 1 value exist in column 2 and vice versa.</p>
  
  <p>sample table </p>
  
  <pre><code>id     id1
  -------------    
  1      2     
  2      1     
  3      4     
  4      3     
  5      6     
  6      5     
  7      8     
  8      7
  </code></pre>
  
  <p>I want to delete 1 row from first two rows, same from third and forth, same for fifth and sixth and so on..</p>
  
  <p>Can anyone please help?</p>