title: how to write a migration to alter a table column from float to bigint in Rails
body: <p>I have data in a Users table.
  One column called :provider_user_id of datatype float.</p>
  
  <p>I want to change it to data type bigint.</p>
  
  <p>How should I write this migration in rails 3</p>
  
  <p>The original column was created with the following migration:</p>
  
  <pre><code>class AddFbuidToUsers &lt; ActiveRecord::Migration
    def self.up
      add_column :users, :provider_user_id, :float
    end
  
    def self.down
      remove_column :users, :provider_user_id
    end
  end
  </code></pre>