title: ALTER TABLE not letting me set NULL or default value?
body: <p>I am trying to change an existing column in a table I have to allow for null values and then set the default value to null.  I tried running the following but it does not seem to be updating the table:</p>
  
  <pre><code>mysql&gt; ALTER TABLE answers_form MODIFY sub_id int unsigned NULL DEFAULT NULL;
  Query OK, 0 rows affected (0.00 sec)
  Records: 0  Duplicates: 0  Warnings: 0
  
  mysql&gt; desc answers_form;
  +--------------+------------------+------+-----+---------+-------+
  | Field        | Type             | Null | Key | Default | Extra |
  +--------------+------------------+------+-----+---------+-------+
  | answer_id    | int(10) unsigned | NO   | PRI | 0       |       |
  | sub_id       | int(10) unsigned | NO   | PRI | 0       |       |
  | form_id      | int(10) unsigned | NO   | PRI | NULL    |       |
  | value        | varchar(255)     | NO   |     | NULL    |       |
  | non_response | bit(1)           | YES  |     | b'0'    |       |
  +--------------+------------------+------+-----+---------+-------+
  5 rows in set (0.01 sec)
  </code></pre>
  
  <p>Can anyone see what I am doing wrong here?</p>