gistfile1.rb

class User < ActiveRecord::Base
  has_many :items
...
  def self.ranked(year)
    select("rank() OVER(ORDER BY SUM(items.amount) DESC), users.*, SUM(items.amount) AS grand_total")
      .joins(:items)
      .where("EXTRACT(YEAR FROM items.sold_at)=:year", year: year)
      .group("users.id")
  end
end