Here's a simple migration I'd like to run :

class AddTimeOfRevisionToBrandWikis < ActiveRecord::Migration
  def self.up
    add_column :brand_wikis, :time_of_revision, :datetime
  end

  def self.down
    remove_column :brand_wikis, :time_of_revision
  end
end

Here's what I get when I try to run it :

$ rake db:migrate
(in /Users/kouak/Documents/workspace/wtb)
You have 1 pending migrations:
  20100404115341 AddTimeOfRevisionToBrandWikis
Run "rake db:migrate" to update your database then try again.

What's wrong with rake db:migrate ?