title: Is it possible to change column index in rails 3 migration?
body: <p>I have a table 'users' with column 'email'. It used to be unique (with index), but a new requirement is to allow nils there. </p>
  
  <p>Is there a better solution than:</p>
  
  <pre><code>  remove_index :users, :email
    add_index :users, :email
  </code></pre>
  
  <p>?</p>
  
  <p>Initially it was added with option unique:</p>
  
  <pre><code>add_index :users, :email, :unique =&gt; true
  </code></pre>