title: Postgresql update column when passed condition
body: <p>Is it possible, and if so, how can the following change be achieved?</p>
  
  <p>Given the table: </p>
  
  <pre><code>param_tab
  param_id serial
  value integer
  anothervalue integer
  update_date TIMESTAMP
  </code></pre>
  
  <p>I would like to do something similar to this: </p>
  
  <pre><code>UPDATE param_tab pt
  CASE WHEN CONDITION THEN pt.value = 14, pt.anothervalue = 20 END
  pt.update_date = someTimestamp;
  </code></pre>
  
  <p>So <code>update_date</code> is always updated and <code>value</code> and <code>anothervalue</code> only in case of some condition</p>