List<Test> list = new List<Test>();
            list.Add(new Test { score = 10, name = "张君宝" });
            list.Add(new Test { score = 20, name = "刘惜君" });
            list.Add(new Test { score = 20, name = "刘惜君" });
            list.Add(new Test { score = 30, name = "八戒" });

            int total = (from temp in list
                         where temp.name == "刘惜君"
                         select temp.age).Count();

            int score = (from temp in list
                         where temp.name == "刘惜君"
                         select temp.score).Sum();
            this.textBox1.Text = "刘惜君：" + total + "人" + score + "score";

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

namespace StartExe
{
    public partial class Form1 : Form
    {
        private List<Test> AllData = new List<Test>();
        private List<Test> PartData = new List<Test>();
        public Form1()
        {
            InitializeComponent();

            AllData.Add(new Test { score = 10, name = "001" });
            AllData.Add(new Test { score = 20, name = "002" });
            AllData.Add(new Test { score = 30, name = "003" });
            AllData.Add(new Test { score = 40, name = "004" });

            PartData.Add(new Test { score = 30, name = "003" });
            PartData.Add(new Test { score = 40, name = "004" });
        }

        //方法：Linq
        private void btnLinq_Click(object sender, EventArgs e)
        {
            LinqMethod(AllData, PartData);
        }

        private void LinqMethod(List<Test> allData, List<Test> partData)
        {
            var query = from a in allData.AsEnumerable()
                        join p in partData.AsEnumerable()
                        on a.score equals p.score into tmp
                        from current in tmp.DefaultIfEmpty()
                        where current == null
                        select new
                        {
                            Name = a.name,
                            SCORE = a.score,
                        };

            string str = string.Empty;
            foreach (var item in query)
            {
                str += item.SCORE + "==" + item.Name + "\r\n";
            }

            this.txtLinq.Text = "linq方式：\r\n" + str + query.Count().ToString();
            //MessageBox.Show(str);
        }

        //方法：Lambda
        private void btnLambda_Click(object sender, EventArgs e)
        {
            LambdaMethod(AllData, PartData);
        }

        private void LambdaMethod(List<Test> AllData, List<Test> PartData)
        {
            var query = AllData.AsEnumerable()
                .GroupJoin
                (
                    PartData.AsEnumerable(),
                     x => x.score, y => y.score, (x, y) => y.DefaultIfEmpty()
                        .Where(w => w == null).
                        Select(z => new { SCORE = x.score, Name = x.name })
                 ).SelectMany(x => x);

            string str = string.Empty;
            foreach (var item in query)
            {
                str += item.SCORE + "==" + item.Name + "\r\n";
            }

            this.txtLambda.Text = "lambda方式：\r\n" + str + query.Count().ToString();
            //MessageBox.Show(str);
        }
    }

    public class Test
    {
        public int age { get; set; }
        public string name { get; set; }
        public int score { get; set; }
    }
}