how rails organization join query and sort them

rails_ar_join_sort_demo.rb

class WxUser < ActiveRecord::Base
  has_many :orders, -> { order('id DESC') }
  acts_as_follower
  has_many :shop_wx_user_maps
  belongs_to :shop

  def orders_in_shop(shop_id)
    orders.where(shop_id: shop_id)
  end

  def current_cart
    carts.last || carts.new
  end

  def self.by_paid_count(shop_id)
    # http://stackoverflow.com/questions/3141463/inner-join-with-count-on-three-tables
    %(
      SELECT
        wx_users.*, count(orders.id) AS order_num
      FROM wx_users
        INNER JOIN shop_wx_user_maps ON wx_users.id = shop_wx_user_maps.wx_user_id
        INNER JOIN orders ON orders.wx_user_id = wx_users.id
      WHERE
        orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)
      GROUP BY
        wx_users.id
      ORDER BY
        order_num DESC
    )
    select('wx_users.*', 'count(orders.id) AS order_num').joins(:shop_wx_user_maps, :orders).where("orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)").group("wx_users.id").order("orders.id DESC")
  end

  def self.by_paid_amount(shop_id)
    # http://stackoverflow.com/questions/3141463/inner-join-with-count-on-three-tables
    %(
      SELECT
        DISTINCT(wx_users.id), wx_users.*, SUM(orders.amount) AS order_amount
      FROM wx_users
        INNER JOIN shop_wx_user_maps ON wx_users.id = shop_wx_user_maps.wx_user_id
        INNER JOIN orders ON orders.wx_user_id = wx_users.id
      WHERE
        orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)
      GROUP BY
        wx_users.id
      ORDER BY
        order_amount DESC
    )
    select('DISTINCT(wx_users.id)', 'wx_users.*', 'SUM(orders.amount) AS order_amount').joins(:shop_wx_user_maps, :orders).where("orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)").group("wx_users.id").order("orders.id DESC")
  end

  def self.by_paid_date(shop_id)
    # http://stackoverflow.com/questions/3141463/inner-join-with-count-on-three-tables
    %(
      SELECT
        wx_users.*
      FROM wx_users
        INNER JOIN shop_wx_user_maps ON wx_users.id = shop_wx_user_maps.wx_user_id
        INNER JOIN orders ON orders.wx_user_id = wx_users.id
      WHERE
        orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)
      GROUP BY
        wx_users.id
      ORDER BY
        orders.id DESC
    )
    joins(:shop_wx_user_maps, :orders).where("orders.shop_id = #{shop_id} AND orders.status IN (1, 2, 3)").group("wx_users.id").order("orders.id DESC")
  end
end