title: Mysql : Insert null timestamp into NOT NULL column
body: <p>Mysql version is 5.1.73,there can be only one <code>timestamp</code> column with <code>current_timestamp</code> in <code>deafault</code> or <code>on update</code> clause,so I tried to create table:</p>
  
  <pre><code>create table `temp`( 
    `id` INTEGER NOT NULL auto_increment PRIMARY KEY, 
    `created_date` TIMESTAMP NOT NULL DEFAULT '0000-00-00 00:00:00',
    `last_updated_date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
  );
  </code></pre>
  
  <p>And after I executed this sql:</p>
  
  <pre><code>insert into `temp`(id,created_date, last_updated_date) values(1,null, null); 
  </code></pre>
  
  <p>I got this document:</p>
  
  <pre><code>1   2017-02-10 18:17:16 2017-02-10 18:18:13
  </code></pre>
  
  <p>Here is my question:</p>
  
  <ul>
  <li>I set <code>created_date</code> NOT NULL,why did the insert sql work well?Should it return <code>Error: Column 'xx' cannot be null</code>？</li>
  <li>Why did <code>created_date</code> column get a value and it is not the <strong>default value</strong>?</li>
  </ul>
  
  <p>Thanks.</p>