Fatch data from database to Checkbox List ON Selection of Checkbox list

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C#

ASP.NET

I have 3 levels of selection.
In the first level have to disply all the Country in a check box list from the database.
The user is allowed to select any number of Countries and based on those selections
I have to show the States which comes under each Countries in seperate checkbox lists.
The user is allowed to select any number of States and based on these selections
I have to show the disttric of each selected States.
please help to solve it.

i am using followind code but it is not working proper

MySqlConnection con;
con = new MySqlConnection(ConfigurationManager.ConnectionStrings["con"].ToString());

con.Open();
try
{

   for (int i = 0; i < CblistCountry.Items.Count; i++)
   {
      if (CblistCountry.Items[i].Selected)
      {
         string var = string.Empty;
         var += CblistCountry.Items[i].Value.ToString();


         string str = "SELECT * FROM add_state where COUNTRYID='" + var + "'";
         MySqlCommand cmd;
         cmd = new MySqlCommand(str, con);
         MySqlDataAdapter da = new MySqlDataAdapter(cmd);
         DataSet ds = new DataSet();
         da.Fill(ds);


      if (ds.Tables[0].Rows.Count > 0)
      {
         CblistState.DataSource = ds;
         CblistState.DataTextField = "StateName";
         CblistState.DataValueField = "StateID";
         CblistState.DataBind();
      }
    }
  }
}
catch
{

}

}