Join on a query result in CSharp

   //  w w w  . j a v  a 2s. c om
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Reflection;

class Salary
{
    int _id;
    int _year;
    double _salary;

    public int ID
    {
        get { return _id; }
        set { _id = value; }
    }

    public int Year
    {
        get { return _year; }
        set { _year = value; }
    }

    public double SalaryPaid
    {
        get { return _salary; }
        set { _salary = value; }
    }
}
class Employee
{
    int _id;
    int _idRole;
    string _lastName;
    string _firstName;

    public int ID
    {
        get { return _id; }
        set { _id = value; }
    }

    public int IDRole
    {
        get { return _idRole; }
        set { _idRole = value; }
    }

    public string LastName
    {
        get { return _lastName; }
        set { _lastName = value; }
    }

    public string FirstName
    {
        get { return _firstName; }
        set { _firstName = value; }
    }
}
class MyRole
{
    int _id;
    string role;

    public int ID
    {
        get { return _id; }
        set { _id = value; }
    }

    public string Role
    {
        get { return role; }
        set { role = value; }
    }
}

public class MainClass
{
    public static void Main()
    {
        List<Employee> people = new List<Employee> {
               new Employee { ID = 1, IDRole = 1, LastName = "A", FirstName = "B"},
               new Employee { ID = 2, IDRole = 2, LastName = "G", FirstName = "T"},
               new Employee { ID = 3, IDRole = 2, LastName = "G", FirstName = "M"},
               new Employee { ID = 4, IDRole = 3, LastName = "C", FirstName = "G"}
            };
        List<MyRole> roles = new List<MyRole> {
               new MyRole { ID = 1, Role = "Manager" },
               new MyRole { ID = 2, Role = "Developer" }
            };
        List<Salary> salaries = new List<Salary> {
               new Salary { ID = 1, Year = 2004, SalaryPaid = 10.00 },
               new Salary { ID = 1, Year = 2005, SalaryPaid = 15.00 },
               new Salary { ID = 1, Year = 2005, SalaryPaid = 15.00 }
            };
        var query = from p in people
                    join s in salaries on p.ID equals s.ID
                    select new { p.FirstName, p.LastName, s.SalaryPaid };

        var querySum = from q in query
                       group q by q.LastName into gp
                       select new { LastName = gp.Key, TotalSalary = gp.Sum(q => q.SalaryPaid) };
        foreach (var v in querySum)
        {
            Console.WriteLine(v.LastName);
        }
    }
}