Update specific column of List using Entity Framework in ASP.Net MVC

After joinning the joined column values are adding like 

EMPID   EMPNAME  AGE DEPNAME

1          SANVI      23    SWA

2          SAI          23    AWS

But for me its adding like 

EMPID   EMPNAME AGE DEPNAME

1           SANVI      23    0

2           SAI         23     0

0           0             0       SWA

0            0            0       AWS

Its adding into the new rows.

Can You please solve me in this issue.

When I try to put Update in place of Add in below code its not working . 

        public ActionResult AddEmp()
        {
            EmployeeEntities3 entities = new EmployeeEntities3();
            List<Emp> employees = entities.Emps.ToList();
            string constr = ConfigurationManager.ConnectionStrings["Constring"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                string query = "Select [Emp].EMPID,[Emp].EMPNAME,[Emp].AGE,[Department].DEPNAME from Emp INNER JOIN Department ON [Emp].[DEPID]=[Department].[DEPID]";
                using (SqlCommand cmd = new SqlCommand(query))
                {
                    cmd.Connection = con;
                    con.Open();
                    using (SqlDataReader sdr = cmd.ExecuteReader())
                    {
                        if (sdr.HasRows)
                        {
                            while (sdr.Read())
                            {
                                employees.Add(new Emp
                                {
                                    // DEPID = System.Convert.ToInt32(sdr["DEPID"]),
                                    DEPNAME = sdr["DEPNAME"].ToString()
                                });

                            }
                        }
                    }
                    con.Close();
                }
            }

            if (employees.Count == 0)
            {
                employees.Add(new Emp());
            }

            List<Department> departments = GetDepartmentList();
            List<SelectListItem> items = new List<SelectListItem>();

            foreach (Department d in departments)
            {
                items.Add(new SelectListItem
                {
                    Text = d.DEPNAME,
                    Value = d.DEPID.ToString()
                });
            }

            var tuple = new Tuple<List<SelectListItem>, List<Emp>>(items, employees);

            return View(tuple);
        }

                        if (sdr.HasRows)
                        {
                            while (sdr.Read())
                            {
                                employees.Add(new Emp
                                {
                                    // DEPID = System.Convert.ToInt32(sdr["DEPID"]),
                                    DEPNAME = sdr["DEPNAME"].ToString()
                                });
                            }