asp.net ajax

<script language="javascript" type="text/javascript">
        function CheckUser() {
            var userName = $("#tbName").val();
            $.ajax({
                type: "GET",
                url: "CheckUser.ashx",
                data: "name=" + userName,
                dataType: 'html',
                error: function () {
                    alert("出错");
                },
                success: function (msg) {
                    if (msg == "hasExist") {
                        $("#divShow").html("<h4>此帐号已经存在</h4>");
                    }
                    else if (msg == "notExist") {
                        $("#divShow").html("<h4>此帐号可以注册</h4>");
                    }
                }
            });
        }
    </script>

后端：

public void ProcessRequest(HttpContext context)
        {
            try
            {
                string name = context.Request.QueryString["name"];
                string connstr = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
                MySqlConnection conn = new MySqlConnection(connstr);
                conn.Open();
                MySqlCommand sd = new MySqlCommand("select * from test where name='" + name + "'", conn);
                MySqlDataAdapter sda = new MySqlDataAdapter();
                sda.SelectCommand = sd;
                DataSet ds = new DataSet();
                sda.Fill(ds);
                context.Response.ContentType = "text/plain";
                if (ds != null && ds.Tables[0].Rows.Count > 0)
                {
                    context.Response.Write("hasExist");
                }
                else
                {
                    context.Response.Write("notExist");
                }
            }
            catch (Exception ex)
            {
                context.Response.Write("出错:"+ex.Message);
            }
        }