How to show selected record from grid view to another page?

Description:
Grid view is used to display records from database some time we need to edit that data instead of grid view edit option we want to send that details another page and update that record values from that values. So I used the Link Button in the grid view for show user Identity Primary key value if user click that link button I send that value as query string to another page.

How to send selected record ID field as query string?
Here I used GridView1_RowCommand event for send user selected record identity value.I check that user command event use of "e.CommandName" if match command value then redirect to another page.
Below code is send value through query string

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "cmdBind")
        {
            LinkButton lb = (LinkButton)e.CommandSource;

            Response.Redirect("Default2.aspx?sid=" + lb.Text + "");
        }

    }

if (!Page.IsPostBack)
        {
            String sid = Request.QueryString["sid"];
            if (sid == "")
            {
                Response.Write("Invalid Student ID");
                return;
            }
            sqlcmd = new SqlCommand("select * from stud where sid='" + sid + "'", sqlcon);
            sqlcon.Open();
            da = new SqlDataAdapter(sqlcmd);
            dt.Clear();
            da.Fill(dt);
            if (dt.Rows.Count > 0)
            {
                TextBox1.Text = sid;
                TextBox2.Text = dt.Rows[0][1].ToString();
                TextBox3.Text = dt.Rows[0][2].ToString();
            }
            sqlcon.Close();
        }