Instead of a blank migration, a commented out but moderately complex example (using the name from the cli)

new.rb

# class AddCategories < ActiveRecord::Migration
#   def up
#     create_table :categories do |t|
#       t.string :name
#       t.integer :score
#       ... # other examples
#   	end
#   end

#   def down
#   	drop_table :categories
#   end
# end

old.rb

class AddCategories < ActiveRecord::Migration
  def up
  end

  def down
  end
end