sql_random.rb

module SqlRandom
  module Relation
    def shuffled
      rand_cmd = if connection.adapter_name =~ /mysql/i
        'rand()'
      else
        'random()'
      end
      clone.order(rand_cmd)
    end
  end

  module Base
    def shuffled
      relation.shuffled
    end

    def random
      shuffled.limit(1).first
    end
  end
end

class ActiveRecord::Relation
  include SqlRandom::Relation
end

class ActiveRecord::Base
  extend SqlRandom::Base
end