How do I update single field in the database without updating the other fields using MVC?

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C#

ASP.NET

MVC

How do I update single field in the database without updating the other fields using MVC?

The sample code blew, I want to update only the field "PROJECTINITIALAPPROVALSTATUS" but it update the other fields with null values.

[HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult SuggestedProjectApproval([Bind(Include = "RECID,PROJECTNO,PROJECTDESC,PROJECTTEAMLEADERID,PROJECTYEAR,PROJECTINITIALAPPROVALSTATUS,PROJECTINITIALAPPROVALNOTES")] STUDY_PROJECTS studyProject, string Approve, string Refuse)
    {
        if (ModelState.IsValid)
        {
             db.Entry(studyProject).State = EntityState.Modified;
            if (!string.IsNullOrEmpty(Approve))
            {
                studyProject.PROJECTINITIALAPPROVALSTATUS = 1;
            }
            else if (!string.IsNullOrEmpty(Refuse))
            {

                studyProject.PROJECTINITIALAPPROVALSTATUS = 2;
            }

            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(studyProject);
    }