title: Convert date to datetime or timestamp using alter table in mysql
body: <p>I have a table in mysql with DATE column, now I need to convert these values to DATETIME or TIMESTAMP.</p>
  
  <p>I wonder what will happen with data when I'll do:</p>
  
  <pre><code>ALTER TABLE sample MODIFY sample_date DATETIME
  </code></pre>
  
  <p>or</p>
  
  <pre><code>ALTER TABLE sample MODIFY sample_date TIMESTAMP
  </code></pre>