title: Error in setting the default value to CURRENT_TIMESTAMP
body: <p>I am having problem while altering a table. I need a column with data type DATETIME to take default value as current date/time and on update also it should automatically update it's value to current date/time. I am writing the following SQL</p>
  
  <pre><code>ALTER TABLE `groups` 
  CHANGE COLUMN `modified` `modified` DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
  </code></pre>
  
  <p>I am getting the following error message.</p>
  
  <pre><code>Error Code: 1067. Invalid default value for 'modified'
  </code></pre>
  
  <p>The MySQL version I'm using is 5.5.49 on a Ubuntu 14.04.1 system.</p>
  
  <p>Please let me know how this can be fixed.</p>