Merge two DataTable and display the result in GridView using C# in ASP.Net

private void Populatebooks()
{
    string Populatebooks = "GetUserPOSTS";
    using (SqlConnection con = new SqlConnection(constring4))
    {
        con.Open();
        using (SqlCommand cmd = new SqlCommand(Populatebooks, con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@UserName", Session["userName"]);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            ViewState["DataTable"] = dt;

            this.Populatebooks2(dt);
            string username5 = this.Page.User.Identity.Name;
        }
    }
}
private void Populatebooks2(DataTable dt)
{
    string Populatebooks = "GetUserPOSTS";
    using (SqlConnection con = new SqlConnection(constring4))
    {
        con.Open();
        using (SqlCommand cmd = new SqlCommand(Populatebooks, con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@UserName", Session["userName"]);
            SqlDataAdapter sdaa = new SqlDataAdapter(cmd);
            DataTable dt2 = new DataTable();
            sdaa.Fill(dt2);
            GetMergedAll.DataSource = dt2;
            GetMergedAll.DataBind();

            //merging first data table into second data table 
            dt2.Merge(dt);
            dt2.AcceptChanges();
            GridView3.DataSource = dt2;
            GridView3.DataBind();
        }
    }
}