string s="name";
if(s=="name")
{
var q =（
 from e in db.Student
 orderby e.name
 select e.name）.Distinct();
 }
else if(s=="age")
{
  var q =
 (from e in db.Student
 orderby e.age
 select e.age).Distinct();;
}

------解决方案--------------------
 public class Person
       {
           public string FirstName { set; get; }
           public string LastName { set; get; }
           public bool sex { get; set; }
       }

       private void Window_Loaded(object sender, RoutedEventArgs e)
       {
           List<Person> classes1 =  new List<Person>();
           classes1.Add(new Person() { FirstName = "Kim", LastName = "Tom", sex = true });
           classes1.Add(new Person() { FirstName = "Kim", LastName = "Tom1", sex = true });
           classes1.Add(new Person() { FirstName = "Kim", LastName = "Tom2", sex = true });
           classes1.Add(new Person() { FirstName = "Kim", LastName = "Tom3", sex = true });
           classes1.Add(new Person() { FirstName = "Kim", LastName = "Tom4", sex = true });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry", sex = false });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry1", sex = false });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry2", sex = false });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry3", sex = false });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry4", sex = false });
           classes1.Add(new Person() { FirstName = "Kyo", LastName = "Jerry5", sex = false });

           var childern = from child in classes1.Where<Person>(p => p.GetType().GetProperty("FirstName").GetValue(p, null).ToString() == "Kim") select child;

           foreach (Person p in childern)
           {
               MessageBox.Show(p.LastName);
           }

       }
我试验了下 貌似没有问题啊， 对linq 不熟，感觉你的问题还是出在数据的结构上， 再仔细看看吧 哈哈

------解决方案--------------------
如果字段太多，建议你先做一个Dictionary来确定Lambda表达式
例子：
  public class PeopleCntorl
   {
       public Dictionary<string, IEnumerable<people>> Dic;
       public PeopleCntorl()
       {
           List<people> peoples = new List<people>()  
           {
               new people{ID=0, Name="Rose", Age=21 },  
               new people{ID=1, Name="Jack", Age=23 },
               new people{ID=2,Name="Mike",Age=29}
           };

           Dic = new Dictionary<string, IEnumerable<people>>(); 
          
           IEnumerable<people> people=from x in peoples
                                      select x.Name;
           IEnumerable<people> people2 = from x in peoples
                                        select x.Age;
           Dic.Add("1", people);
           Dic.Add("2", people2);
       }

       public IEnumerable<people> GetEnumerable(string name)
       {
           IEnumerable<people> iEnumerale=Dic[name];