Izvrsavanje queryja (postoji li greska u kodu)

Code:
using System;
using System.Data;
using System.Configuration;
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.SqlClient;


public partial class Korpa : System.Web.UI.Page
{
    protected void Button1_Click(object sender, EventArgs e)
    {
        System.Data.SqlClient.SqlConnection konekcija = new System.Data.SqlClient.SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename=|DataDirectory|\\Proba.mdf;Integrated Security=True;User Instance=True");
        
        konekcija.Open();
        if (Request.QueryString[0].Equals("isprazni"))
        {
            SqlCommand komanda = new SqlCommand("DELETE FROM Stavke_racun WHERE Racun_idRacuna in (select                   max(Racun_idRacuna) from Stavke_racun)", konekcija);
            komanda.ExecuteNonQuery();
            SqlDataSource1.Delete();
        }
    }
}

Code:
string qstring = Request.QueryString[0].ToString();