在查询表达式中，子 orderby 句按升序或降序对返回的序列或子序列（组）进行排序。 可以指定多个键来执行一个或多个辅助排序作。 元素类型的默认比较器执行排序。 默认的排序顺序为升序。 还可以指定自定义比较器，但只能使用基于方法的语法提供它。 有关详细信息，请参阅 “对数据进行排序”。
C# 语言参考记录了 C# 语言的最新发布版本。 它还包含即将发布的语言版本公共预览版中功能的初始文档。
本文档标识了在语言的最后三个版本或当前公共预览版中首次引入的任何功能。
小窍门
若要查找 C# 中首次引入功能时，请参阅 有关 C# 语言版本历史记录的文章。
在以下示例中，第一个查询按字母顺序对从 A 开始的单词进行排序，第二个查询按降序对相同的单词进行排序。 （关键字 ascending 是默认排序值，可以省略。
class OrderbySample1
{
static void Main()
{
// Create a delicious data source.
string[] fruits = ["cherry", "apple", "blueberry"];
// Query for ascending sort.
IEnumerable<string> sortAscendingQuery =
from fruit in fruits
orderby fruit //"ascending" is default
select fruit;
// Query for descending sort.
IEnumerable<string> sortDescendingQuery =
from w in fruits
orderby w descending
select w;
// Execute the query.
Console.WriteLine("Ascending:");
foreach (string s in sortAscendingQuery)
{
Console.WriteLine(s);
}
// Execute the query.
Console.WriteLine(Environment.NewLine + "Descending:");
foreach (string s in sortDescendingQuery)
{
Console.WriteLine(s);
}
}
}
/* Output:
Ascending:
apple
blueberry
cherry
Descending:
cherry
blueberry
apple
*/
以下示例对学生的姓氏执行主要排序，然后对学生的名字执行次要排序。
class OrderbySample2
{
// The element type of the data source.
public class Student
{
public required string First { get; init; }
public required string Last { get; init; }
public int ID { get; set; }
}
public static List<Student> GetStudents()
{
// Use a collection initializer to create the data source. Note that each element
// in the list contains an inner sequence of scores.
List<Student> students = new List<Student>
{
new Student {First="Svetlana", Last="Omelchenko", ID=111},
new Student {First="Claire", Last="O'Donnell", ID=112},
new Student {First="Sven", Last="Mortensen", ID=113},
new Student {First="Cesar", Last="Garcia", ID=114},
new Student {First="Debra", Last="Garcia", ID=115}
};
return students;
}
static void Main(string[] args)
{
// Create the data source.
List<Student> students = GetStudents();
// Create the query.
IEnumerable<Student> sortedStudents =
from student in students
orderby student.Last ascending, student.First ascending
select student;
// Execute the query.
Console.WriteLine("sortedStudents:");
foreach (Student student in sortedStudents)
Console.WriteLine(student.Last + " " + student.First);
// Now create groups and sort the groups. The query first sorts the names
// of all students so that they will be in alphabetical order after they are
// grouped. The second orderby sorts the group keys in alpha order.
var sortedGroups =
from student in students
orderby student.Last, student.First
group student by student.Last[0] into newGroup
orderby newGroup.Key
select newGroup;
// Execute the query.
Console.WriteLine(Environment.NewLine + "sortedGroups:");
foreach (var studentGroup in sortedGroups)
{
Console.WriteLine(studentGroup.Key);
foreach (var student in studentGroup)
{
Console.WriteLine(" {0}, {1}", student.Last, student.First);
}
}
}
}
/* Output:
sortedStudents:
Garcia Cesar
Garcia Debra
Mortensen Sven
O'Donnell Claire
Omelchenko Svetlana
sortedGroups:
G
Garcia, Cesar
Garcia, Debra
M
Mortensen, Sven
O
O'Donnell, Claire
Omelchenko, Svetlana
*/
在编译时，子 orderby 句将转换为对方法的 OrderBy 调用。
orderby 子句中的多个关键值将转换为 ThenBy 方法调用。
