```ruby
class AddPasswordChangedAtToUsers < ActiveRecord::Migration
  def change
    add_column :users, :password_changed_at, :datetime
    User.update_all ['password_changed_at = ?', '2013-03-06 20:00:00']
  end
end
```

Set password_changed_at to confirmation date for new users
user
```ruby
class AddPasswordChangedAtToUsers < ActiveRecord::Migration
  def change
    add_column :users, :password_changed_at, :datetime
    User.update_all "password_changed_at = GREATEST('2013-03-06 20:00:00', confirmed_at)"
  end
end
```
assistant