discourse/db/migrate/20121207000741_add_notifications_to_topic_users.rb

class AddNotificationsToTopicUsers < ActiveRecord::Migration
  def change
    add_column :topic_users, :notifications, :integer, default: 2 
    add_column :topic_users, :notifications_changed_at, :datetime
    add_column :topic_users, :notifications_reason_id, :integer
  end
end