Problema IsPostBack

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using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.Odbc;
public partial class admin_user_user_update : System.Web.UI.Page
{
    string ConnectionString = ConfigurationManager.AppSettings["DBConnectionString"];
   
    protected void Page_Load(object sender, EventArgs e)
    {
       

        if (!IsPostBack)
        {
            Popola();
        } 
    }
    private void Popola()
    {
        string str_name = Request.QueryString["user"];
        string str_query = "SELECT * FROM user WHERE user_name='" + str_name + "'";
        OdbcConnection conn = new OdbcConnection(ConnectionString);

        OdbcCommand command = new OdbcCommand(str_query, conn);
        command.Connection.Open();
        OdbcDataReader reader = command.ExecuteReader();

        
        while (reader.Read())
        {
            name.Text = "" + reader["user_name"] + "";
            Firstname.Text = "" + reader["user_firstname"] + "";
            sex.Text = "" + reader["user_sex"] + "";
            birthday.Text = "" + reader["user_birthday"] + "";
            username.Text = "" + reader["user_username"] + "";
            password.Text = "" + reader["user_password"] + "";
            email.Text = "" + reader["user_email"] + "";
            skype.Text = "" + reader["user_skype"] + "";
            msn.Text = "" + reader["user_msn"] + "";
            other.Text = "" + reader["user_other"] + "";
            photo.Text = "" + reader["user_photo"] + "";
            city.Text = "" + reader["user_city"] + "";
            cap.Text = "" + reader["user_cap"] + "";
            address.Text = "" + reader["user_address"] + "";
            telephone.Text = "" + reader["user_telephone"] + "";
            info.Text = "" + reader["user_info"] + "";
            suffering.Text = "" + reader["user_suffering"] + "";
            hate.Text = "" + reader["user_hate"] + "";
            friends.Text = "" + reader["user_friends"] + "";
        }
        
        command.Connection.Close();
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        //string str_id = Request.QueryString["id"];
        string str_name = Request.QueryString["user"];
        OdbcConnection conn = new OdbcConnection(ConnectionString);
        string str_query = "UPDATE user SET user_name='" + name.Text + "',"
        + "user_firstname='" + Firstname.Text + "',"
        + "user_sex='" + sex.Text + "',"
        + "user_birthday='" + birthday.Text + "',"
        + "user_username='" + username.Text + "',"
        + "user_password='" +  password.Text + "',"
        + "user_email='" + email.Text + "',"
        + "user_skype='" + skype.Text + "',"
        + "user_msn='" + msn.Text + "',"
        + "user_other='" + other.Text + "',"
        + "user_photo='" + photo.Text + "',"
        + "user_city='" + city.Text + "',"
        + "user_cap='" + cap.Text + "',"
        + "user_address='" + address.Text + "',"
        + "user_telephone='" + telephone.Text + "',"
        + "user_info='" + info.Text + "',"
        + "user_suffering='" + suffering.Text + "',"
        + "user_hate='" + hate.Text + "',"
        + "user_friends='" + friends.Text + "' WHERE user_name='" + str_name + "'";
        OdbcCommand command = new OdbcCommand(str_query, conn);
        command.Connection.Open();
        command.ExecuteNonQuery();
        Response.Write(str_query);
        command.Connection.Close();
        Response.Redirect("Default.aspx");
    }
}

protected void Button2_Click(object sender, EventArgs e)
    {
        //string str_id = Request.QueryString["id"];
        string str_name = Request.QueryString["user"];

       //..... codice aggiornamento

   Popola();
    }

SELECT <campi> FROM <tabella> WHERE campo1 = @parametro1 AND campo2 = @parametro2..

 OdbcParameter paramPN =
       command.Parameters.Add("@name", OdbcType.VarChar, 255);

user_name=@name

         OdbcParameter param1 =
        command.Parameters.Add("name", OdbcType.VarChar, 255);
        param1.Value = name.Text;

            string str_query = "UPDATE user SET user_name=?,"