display grid based on combobox values

  protected void Button1_Click(object sender, EventArgs e)

    {

        string ComboValue = DropDownList1.SelectedValue.ToString();

        Response.Redirect("Page2.aspx?selected=" + ComboValue);

    }

 protected void Page_Load(object sender, EventArgs e)

    {

        if (!IsPostBack)

        {

            //Rettive the Value From Query String

            string selectedvalue = Request.QueryString[0].ToString();

            if (String.IsNullOrEmpty(selectedvalue) == false)

            {

                SqlConnection con = new SqlConnection("your Connection String");

                con.Open();

                SqlCommand comm = new SqlCommand("select * from Tablename where Columname='" + selectedvalue + "'", con);

                GridView1.DataSource = comm.ExecuteReader();

                DataBind();

            }

        }

    }