title: Get the current value FROM Cassandra - Update USING TIMESTAMP?
body: <p>I create a simple table with timestamp
  how to insert on it the timestampvalue also i want to use the current valueoftimestamp to do UPDATE later ! </p>
  
  <p>I used this instruction:</p>
  
  <pre><code>UPDATE users SET   timestampid =  dateof(now())  WHERE id= userID  ;
  </code></pre>
  
  <p>got this value on my table: </p>
  
  <pre><code>2016-04-14 11:18:12+0200
  </code></pre>
  
  <p>now want to do UPDATE USING This value </p>
  
  <pre><code> UPDATE users USING TIMESTAMP '2016-04-14 11:18:12+0200' SET   timestampid =  dateof(now())  WHERE id= userID  ;
  </code></pre>
  
  <blockquote>
    <p>Invalid null value of timestamp ?</p>
  </blockquote>
  
  <p>How to get the current timestampValue from Cassandra when using:</p>
  
  <pre><code>Update USING TIMESTAMP valueoftimestamp
  </code></pre>
  
  <p>to check if there's Modification or not using timestamp.</p>