title: How to select distinct on specific columns
body: <p>I have few columns in a table</p>
  
  <p><strong>Col1</strong>, <strong>Col2</strong>, <strong>Col3</strong>, <strong>Col4</strong></p>
  
  <p>Now I want to select like this</p>
  
  <p><code>SELECT DISTINCT (Col1, Col2, Col3), Col4</code></p>
  
  <p>i.e. get the distinct based on only these three colunms.</p>