ช่วยดูโค้ดให้หน่อยครับตรง C# StringBuilder sb.Clear(); มันเออเรอ อยากทราบว่าจะแก้ยังไง

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Web.Configuration;
using System.Text;
using System.Data;

public partial class Post : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string strConn;
        strConn = WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection Conn = new SqlConnection(strConn);
        Conn.Open();

        StringBuilder sb = new StringBuilder();
        sb.Append("SELECT TOP 1 TID FROM Topic ORDER BY TID Desc");
        var sqlSave = sb.ToString();

        string LastTID = "";
        SqlCommand com = new SqlCommand();
        SqlDataReader dr;
        com.Connection = Conn;
        com.CommandType = CommandType.Text;
        com.CommandText = sqlSave;
        dr = com.ExecuteReader();
        if (dr.HasRows)
        {
            dr.Read();
            var CurrentTID = dr.GetString(0);
            int Running = Convert.ToInt32(CurrentTID.Substring(1, CurrentTID.Length - 1));
            Running++;
            LastTID = "T" + Running.ToString("0000000");
        }
        else
        {
            LastTID = "T0000001";
        }
        dr.Close();

        sb.Clear();
        sb.Append("INSERT INTO Topic(TID,Topic,Description,UserName,RecordDate,ViewCount,ReplyCount,IP)");
        sb.Append("VALUES (@TID,@Topic,@Description,@UserName,@RecordDate,@ViewCount,@ReplyCount,@IP)");
        sqlSave = sb.ToString();
        com.CommandText = sqlSave;
        com.Parameters.Clear();
        com.Parameters.Add("@TID",SqlDbType.NVarChar).Value = LastTID;
        com.Parameters.Add("@Topic",SqlDbType.NVarChar).Value = txtTopic.Text.Trim();
        com.Parameters.Add("@Description", SqlDbType.NVarChar).Value = txtDescription.Text.Trim();
        com.Parameters.Add("@UserName", SqlDbType.NVarChar).Value = txtUserName.Text.Trim();
        com.Parameters.Add("@RecordDate", SqlDbType.DateTime).Value = DateTime.Now;
        com.Parameters.Add("@ViewCount", SqlDbType.Int).Value = 1;
        com.Parameters.Add("@ReplyCount", SqlDbType.Int).Value = 0;
        com.Parameters.Add("@IP", SqlDbType.NVarChar).Value = Request.ServerVariables["REMOTE_ADDR"];
        com.ExecuteNonQuery();
        Conn.Close();
        Response.Redirect("Default.aspx");
    }
    protected void cmd_Click(object sender, EventArgs e)
    {
        txtTopic.Text = "";
        txtDescription.Text = "";
        txtUserName.Text = "";
    }


    }