dropdown list problem

protected void dropdown_SelectedIndexChanged(object sender, EventArgs e)
{
   
      string conString = @"Data Source=myServerAddress;
        Initial Catalog=myDataBase;User Id=myUsername;Password=myPassword"; 
      SqlConnection con = new SqlConnection(conString);
        string cmd ="";
       if(dropdown.SelectedValue=="0")
       {
          //fetch all the records 
           cmd =  "selet * from myTable";
        }
        else{
         // fetch records on the bais of  Dropdown Selected value
        cmd = "select * form Table where ColumnName=" + SelectedValue  ;
        }
         //open db connection
        con.Open();
         //execute command with data adapter
        SqlDataAdapter sqlDa = new SqlDataAdapter(cmd, con);
        // create a new table 
        DataTable Dt = new DataTable();
          // fill the table with returned Result
        sqlDa.Fill(Dt);
   }
}

<asp:dropdownlist id="dropDown" runat="server" autopostback="true" onselectedindexchanged="dropDown_SelectedIndexChanged" xmlns:asp="#unknown">
    <asp:listitem text="Select" value="0" selected="True"></asp:listitem>
    <asp:listitem text="Item 1" value="1"></asp:listitem>
    <asp:listitem text="Item 2" value="2"></asp:listitem>
</asp:dropdownlist>

protected void dropDown_SelectedIndexChanged(object sender, EventArgs e)
{
    if (dropDown.SelectedValue != "0")
    {
        //Get your filtered data here..
    }
}