title: Rails' datetime and timestamp in a migration file are the same for MySQL and Sqlite3?
body: <p><code>:datetime</code> and <code>:timestamp</code> in a migration file seems like the same in MySQL and Sqlite3, and they both map to <code>datetime</code> in the database side, except I can't find that in a formal documentation.</p>
  
  <p>Also, what about when if our Rails project may use other DBMS, then should we use <code>:datetime</code> or <code>:timestamp</code> when we <code>script/generate</code> (or <code>rails generate</code>) our Model or Scaffold?</p>