title: Update timestamp when row is updated in PostgreSQL
body: <p>In MySQL, we can execute this where it updates the column <code>changetimestamp</code> every time the row is changed:</p>
  
  <pre><code>create table ab (
    id int, 
    changetimestamp timestamp 
      NOT NULL 
      default CURRENT_TIMESTAMP 
      on update CURRENT_TIMESTAMP 
  );
  </code></pre>
  
  <p>Is there something similar to do the above in PostgreSQL?</p>