How would you refactor this? (Rails 1.2, Ruby 1.8.7)

customer_discount.rb

# == Schema Information
# Table name: line_items
#  id                              :integer       not null, primary key
#  item_id                         :integer       not null
#  order_id                        :integer       not null
#  quantity                        :integer       not null
#  discount_percentage             :decimal(18, 2 default(0.0)
#  ... many fields redacted
#
class LineItem < ActiveRecord::Base
  belongs_to :item
  belongs_to :order

  def customer_discount_percentage_quantity business_account_id, group_account_id, voucher_id
       
    if self.item.customer_discount_group_id
      query = "EXEC item_sp_get_customer_discount " +
        "  @quantity                   = #{self.quantity}" +
        ", @business_account_id        = #{business_account_id.blank?? 0:business_account_id} " +
        ", @group_account_id           = #{group_account_id.blank?? 0: group_account_id}" +
        ", @customer_discount_group_id = #{self.item.customer_discount_group_id}"                                             
      result_set = LineItem.find_by_sql(query)  

      voucher_discount_percentage = 0.0 
          
      unless voucher_id.blank?
        voucher_detail = DiscountVoucher.find_by_id(voucher_id)
        unless  voucher_detail.blank?
          unless voucher_detail.voucher_discount_percentage.blank?
            voucher_discount_percentage  = voucher_detail.voucher_discount_percentage
          end 
        end
      end
          
      if result_set[0]!=nil 
        if voucher_discount_percentage > 0
          self.discount_percentage = voucher_discount_percentage
          return ( voucher_discount_percentage)  
        else
          self.discount_percentage = result_set[0].discount_percentage 
          return (result_set[0].discount_percentage )            
        end  
          
      else         
        voucher_discount_percentage
      end
    end
    0.0
  end
end

refactored_customer_discount.rb

# == Schema Information
# Table name: line_items
#  id                              :integer       not null, primary key
#  item_id                         :integer       not null
#  order_id                        :integer       not null
#  quantity                        :integer       not null
#  discount_percentage             :decimal(18, 2 default(0.0)
#  ... many fields redacted
#
class LineItem < ActiveRecord::Base
  belongs_to :item
  belongs_to :order

  def query_discount_percentage quantity, business_account_id, group_account_id, customer_discount_group_id
    query = "EXEC item_sp_get_customer_discount" + 
      "  @quantity                   = #{[quantity.to_i, 1].max}" +
      ", @business_account_id        = #{business_account_id.to_i}" +
      ", @group_account_id           = #{group_account_id.to_i}" +
      ", @customer_discount_group_id = #{customer_discount_group_id.to_i}"                                             

    result = LineItem.find_by_sql(query).first
    result ? result.discount_percentage : 0.0
  end

  def voucher_discount_percentage voucher_id
    if (voucher = DiscountVoucher.find_by_id(voucher_id)) && !voucher.voucher_discount_percentage.blank?
      voucher.voucher_discount_percentage
    end
  end
    
  def customer_discount_percentage_quantity business_account_id, group_account_id, voucher_id
    return 0.0 unless self.item.customer_discount_group_id

    if discount_percent = voucher_discount_percentage(voucher_id)
      return self.discount_percentage = discount_percent
    end

    discount_percent = query_discount_percentage quantity, 
      business_account_id, group_account_id, customer_discount_group_id
    
    self.discount_percentage = discount_percent
  end
end