title: Alter SQL table - allow NULL column value
body: <p>Initially, the table "MyTable" has been defined in the following way:</p>
  
  <pre><code>CREATE TABLE IF NOT EXISTS `MyTable` (
    `Col1` smallint(6) NOT NULL AUTO_INCREMENT,
    `Col2` smallint(6) DEFAULT NULL,
    `Col3` varchar(20) NOT NULL,
  );
  </code></pre>
  
  <p>How to update it in such a way that the column "Col 3" would be allowed to be NULL?</p>