SalesNumber=db.Shop_Order.Join(db.Shop_OrderGoods,o=>o.OrderId,g=>g.OrderId,(o,g)=>new {o,g}).Where(z=>z.o.OrderStatus==1&&z.g.GoodsId==item.GoodsId).Select(z=>z.g.Number).DefaultIfEmpty().Sum()+item.VirtualSalesNum,
原文：https://www.cnblogs.com/firstcsharp/p/11913622.html