public static void UpdateStaff(StaffDTO staff)
{
string strSql = "update NHANVIEN set ho_ten = N'" + staff.ten_nhan_vien + "' ,ngay_sinh = '" + staff.ngay_sinh +
"', dia_chi = N'" + staff.dia_chi + "', dien_thoai = '" + staff.so_dien_thoai + "' where ma_nhan_vien = '" +
staff.ma_nhan_vien + "'";
DataProvider.ExecNonQuery(strSql);
}