通过按钮导向download.aspx?id=10,在同一页面downloads中导向的
public partial class downloads : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.QueryString["id"] == "10")
        {
            string pid = Request.QueryString["id"];
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["sqlcon"].ConnectionString);
            con.Open();
            SqlCommand cmd = new SqlCommand("select urlss from urlss where id='" + pid + "'", con);
            string urlss = Convert.ToString(cmd.ExecuteScalar());
            Response.Redirect(urlss);  //urlss等于"up/yd.exe"
            //Response.Write(htp+urlss);
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Response.Redirect("downloads.aspx?id=10");
    }
}