LINQ - 加入多个列表

// 使用 LINQ to Objects
var query = from item in items
            where item.Price > 100
            select item;

// 使用 LINQ to SQL
var query = from order in orders
            where order.OrderDate > new DateTime(2022, 1, 1)
            select order;

// 使用 LINQ to XML
var query = from order in orders
            where order.OrderDate > new DateTime(2022, 1, 1)
            select new XElement("Order",
                new XAttribute("OrderID", order.OrderID),
                new XAttribute("OrderDate", order.OrderDate.ToString("yyyy-MM-dd"))
            );