How can I convert this migration to raw sql? or Can I convert?

```
class AddUnsubscribeTokenToUsers < ActiveRecord::Migration
  def self.up
    add_column :users, :unsubscribe_token, :string, :unique => 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

```