Dropdown bind in MVC 4

DROPDOWN BIND DYNAMICALLY WITH ENTITY FRAME WORK
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IN CSHTML
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 @Html.DropDownList("Departments", "select department");

IN CONTROLLER
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        [HttpGet]
        public ActionResult Register()
        {
            TestEntities ob = new TestEntities();
            ViewBag.Departments = new SelectList(ob.excels, "Id", "name");
            return View();
        }

note:
excels is table name.
Id and name is column name of table
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DROPDOWN BIND STATIC
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@Html.DropDownList("Departments", new List<SelectListItem>
{ 
    new SelectListItem { Text = "IT", Value = "1", Selected=true},
    new SelectListItem { Text = "HR", Value = "2"},
    new SelectListItem { Text = "Payroll", Value = "3"}
}, "Select Department") 

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WHEN U WANT FIND SELECTED VALUE FROM DATABASE
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"selectedValue" parameter.
ViewBag.Departments = new SelectList(db.Departments, "Id", "Name", "1");