title: Find duplicate entries in database for specific fields
body: <p>I have model having fields as name, school, email, address etc.</p>
  
  <p>I want to find out the rows for which there is same entry for <code>name</code> and <code>school</code> field ?</p>
  
  <pre><code>eg:
  name school email 
  abc     mps    abc@gmail.com
  abc     mps    abc@gmail.com
  xyz     vps    xyz@gmail.com
  abc     mps    abc@gmail.com
  poi     vps    poi@gmail.com
  jkl     vps    jkl@gmail.com
  </code></pre>
  
  <p>like for <code>name</code> abc and <code>school</code> mps ther are 3 entries and for xyz and vps there are 2 entries 
  I can nested <code>for</code> loop and iterative manner to check the name and school fields against all the rows in the table. That would be performance hit (n*n)</p>
  
  <p>Is there any other way to find out ?</p>