title: Convert timestamp column values to epoch in PostgreSQL select query
body: <p>I need to convert timestamp values to epoch in a <code>SELECT</code> query.
  Please find the below sample table and expected result.</p>
  
  <p>Sample table:</p>
  
  <pre><code>select * from log;
  </code></pre>
  
  <pre class="lang-none prettyprint-override"><code>id        | 3
  time      | 2016-03-30 18:44:19.189513
  data1     | NONE
  data3     | NONE
  data4     | NONE
  </code></pre>
  
  <p>Expected result:</p>
  
  <pre class="lang-none prettyprint-override"><code>id        | 3
  time      | 1459343659
  data1     | NONE
  data3     | NONE
  data4     | NONE
  </code></pre>
  
  <p>Log table is having n number of rows. Please find the below version details:</p>
  
  <pre class="lang-none prettyprint-override"><code>select version();
  
  version                                            
  ----------------------------------------------------------------------------------------------
   PostgreSQL 9.3.5 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.7.2-5) 4.7.2, 64-bit
  </code></pre>