title: Convert Rails migration to raw SQL
body: <p>How can I convert this migration to raw sql? or Can I convert?</p>
  
  <pre><code>class AddUnsubscribeTokenToUsers &lt; ActiveRecord::Migration
    def self.up
      add_column :users, :unsubscribe_token, :string, :unique =&gt; true
      User.all.each do |user|
          user.unsubscribe_token = ActiveSupport::SecureRandom.hex(18)
      end
    end
    def self.down
      remove_column :users, :unsubscribe_token
    end
  end
  </code></pre>