Lamda, Northwind, get avg() Discount

       var averageCountryCompanyDiscountLambda =
                    db.Customers.Join(db.Orders, customers => customers.CustomerID, orders => orders.CustomerID,
                        (customers, orders) => new { customers, orders })
                        .Join(db.Order_Details, @t => @t.orders.OrderID, orderDetails => orderDetails.OrderID,
                            (@t, orderDetails) => new { @t, orderDetails })
                        .GroupBy(@t => new
                        {
                            @t.@t.customers.CompanyName,
                            @t.@t.customers.Country
                        }, @t => new { Customers = @t.@t.customers, OrderDetails = @t.orderDetails })
                        .OrderBy(g => g.Key.Country)
                        .Select(g => new
                        {
                            g.Key.CompanyName,
                            g.Key.Country,
                            Discount = g.Average(p => p.OrderDetails.Discount)
                        });