Problem with users login history

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C#

ASP.NET

SQL-Server

Dear Friendss,

I have a Webapplication project, in that i used to display users login and logout history.

On my webform I have a Gridview which is used to display Users Login History.

I used a Method to display the data in gridview and binded it....its displaying fine.
I didnt use Gridview boundfields to display the data.

In this Gridview I used fields as userid,username, login_time, logout_time and also i need to display the Duration time from login to logout as 2 hours something like this.

the time between login and logout is displaying...but it doesnt show column header in Gridview as duration.

I took Duration Field in Database....but unable to display.

This is my code.

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
using System.Web.Configuration;

public partial class Users_UserLoginHistory : System.Web.UI.Page
{
    string conString = ConfigurationManager.ConnectionStrings["infosystemDBConnectionString"].ToString();

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            GridData();
        }

    }
    protected void BtnGo_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(conString);


        //SqlCommand cmd = new SqlCommand("Select LogId,UserName,Login_Time,Logout_Time from UserLogs where UserName='" + TxtSearch.Text + "' order by Login_Time desc", con);
        SqlCommand cmd = new SqlCommand("Select LogId,UserName,Login_Time,Logout_Time,convert(nvarchar,datediff(mi,Login_Time,Logout_time))) + ' Mins ' from UserLogs where UserName='" + TxtSearch.Text + "' order by Login_Time desc", con);
        

        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        Grid1.DataSource = dt;
        Grid1.DataBind();
    }

    private void GridData()
    {
        SqlConnection con = new SqlConnection(conString);

        SqlCommand cmd = new SqlCommand("Select LogId,UserName,Login_Time,Logout_Time from UserLogs order by Login_Time desc", con);

        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        Grid1.DataSource = dt;
        Grid1.DataBind();

    }
}

Please solve my problem and give me a perfect solution. i need header as duration.

Thanks in Advance.

[edit]Code block added - OriginalGriff[/edit]