更新数据库

SqlConnection con = db.creatconnection();
        con.Open();
        SqlCommand upcmd = new SqlCommand();
        upcmd.Connection = con;
        upcmd.CommandText = "update voteDetails set voteNum=voteNum+1 where voteDetailsID="+this.RadioButtonList1.SelectedValue.ToString();
        upcmd.ExecuteNonQuery();
提示:第 1 行: '=' 附近有语法错误。不知道是什么问题!是不是哪里写错了.