Dictionary use for filter by Alfabet .net

--------------aspx---------------
 <div>
    <asp:Repeater ID="FilteringUI"  runat="server" OnItemCommand="FilteringUI_ItemCommand">
            <ItemTemplate>
                <asp:LinkButton runat="server" ID="lnkFilter" Text='<%# Container.DataItem %>' CommandName='<%# Container.DataItem %>'>
                </asp:LinkButton>
            </ItemTemplate>
            <SeparatorTemplate>
                |</SeparatorTemplate>
        </asp:Repeater>
    </div>
    <asp:GridView ID="gridUsers" runat="server">
        </asp:GridView>
--------------------cs--------------------------------
using System;
using System.Data;
using System.Data.SqlClient;
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;

public partial class birla_xml_loc_panel_Directory : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        BindFilteringUI();
    }
    private void BindFilteringUI()
    {
        string[] filterOptions = { "All", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };
        FilteringUI.DataSource = filterOptions;
        FilteringUI.DataBind();
    }
    protected void FilteringUI_ItemCommand(object source, RepeaterCommandEventArgs e)
    {
        if (e.CommandName == "All")
            this.UsernameToMatch = string.Empty;
        else
            this.UsernameToMatch = e.CommandName;
        BindUserAccounts();
    }
     private void BindUserAccounts()
    {
       
        if (this.UsernameToMatch == "")
        {SqlConnection con =new SqlConnection ("server=10.0.0.11;database=planetm;uid=sa;pwd=sa;");
            DataSet ds=new DataSet ();
            SqlDataAdapter da=new SqlDataAdapter ("select username,lastname from UserProfile ",con);
            da.Fill (ds);
            gridUsers.DataSource = ds;
            gridUsers.DataBind();
        }
        else
        {
            string str = this.UsernameToMatch;
            SqlConnection con = new SqlConnection("server=10.0.0.11;database=planetm;uid=sa;pwd=sa;");
            DataSet ds = new DataSet();
            SqlDataAdapter da = new SqlDataAdapter("select username,lastname from UserProfile where username like '" + str + "%' ", con);
            da.Fill(ds);
            gridUsers.DataSource = ds;
            gridUsers.DataBind();
        }
    }
    private string UsernameToMatch
    {
        get
        {
            object o = ViewState["UsernameToMatch"];
            if (o == null)
                return string.Empty;
            else return (string)o;
        }
        set
        {
            ViewState["UsernameToMatch"] = value;
        }
    }
}