title: PostgreSQL 9.3: Add/Remove QUARTER to/from timestamp
body: <p>I want to add the <code>QUARTER</code> to the <code>TIMESTAMP</code> in PostgreSQL 9.3 version.</p>
  <h3>My Try:</h3>
  <p>For adding:</p>
  <pre><code>SELECT TIMESTAMP '2016-01-01' + INTERVAL '01 QUARTER';
  </code></pre>
  <p>For remove:</p>
  <pre><code>SELECT TIMESTAMP '2016-01-01' - INTERVAL '01 QUARTER';
  </code></pre>
  <blockquote>
  <pre><code>********** Error **********  
  ERROR: invalid input syntax for type interval: &quot;01 QUARTER&quot;  
  SQL state: 22007  
  Character: 42
  </code></pre>
  </blockquote>