zz.diff

     where(person_id: Person.find_by(email: email, site_id: site_id), site_id: site_id)
   }

+  scope :by_coupon_list, ->(coupon_list_id) {  
+    sub_query = Coupon.  
+      joins('INNER JOIN `checkout_coupons` ON `checkout_coupons`.`coupon_id` = `coupons`.`id`').  
+      where('`origins`.`id` = `checkout_coupons`.`purchase_id`').where(coupon_list_id: coupon_list_id)  
+    where("exists (#{sub_query.to_sql})")  
+  }
+
   scope :with_mobile_visitor, ->(mobile) {
     return if mobile.nil?
     joins(:visitor).merge(Visitor.mobile(mobile))