title: I thought curtime(), now() and current_timestamp are valid default datetime values in MySql?
body: <p>I'm using the latest version of MySql and I tried altering a table to use curtime() or now() or current_timestamp as the default value for a datetime column (created_at, updated_at). For all three, the alter failed, saying these are invalid default values. Any ideas what's an appropriate default value to generate the current time in a datetime field?</p>
  
  <pre><code>ALTER TABLE `music_library_development`.`albums` 
  MODIFY COLUMN `created_at` DATETIME NOT NULL DEFAULT current_timestamp,
  MODIFY COLUMN `updated_at` DATETIME NOT NULL DEFAULT current_timestamp;
  
  ALTER TABLE `music_library_development`.`albums` 
  MODIFY COLUMN `created_at` DATETIME NOT NULL DEFAULT now(),
  MODIFY COLUMN `updated_at` DATETIME NOT NULL DEFAULT now();
  
  ALTER TABLE `music_library_development`.`albums` 
  MODIFY COLUMN `created_at` DATETIME NOT NULL DEFAULT curtime(),
  MODIFY COLUMN `updated_at` DATETIME NOT NULL DEFAULT curtime();
  </code></pre>