Exporting unknown table format to excel & exclude selected fields

    protected void Button1_Click(object sender, EventArgs e)
    {
        string fichpath = ConfigurationManager.AppSettings["ruta"].ToString();
        string fich = "errores.xls";
        string cols = "";
        string colstype = "";
        bool flg = false;
        string nombretabla = "HS_IZ_CLIENTES";
        string fecha = "20130820";
        DataTable tabla = new DataTable("errores");
 
        try
        {
            SqlConnection cnx = new SqlConnection();
            cnx.ConnectionString = ConfigurationManager.ConnectionStrings["HSSIAAF"].ToString();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = cnx;
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "SELECT COLUMN_NAME,DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '" + nombretabla + "' AND COLUMN_NAME NOT IN ('LINEA','ERROR','CHECKS','ERRORS','LINEAC')";
            cnx.Open();
            SqlDataReader dr = cmd.ExecuteReader();
 
            if (File.Exists(fichpath + fich))
                File.Delete(fichpath + fich);
 
            using (System.Data.OleDb.OleDbConnection con = new System.Data.OleDb.OleDbConnection(
                "Provider=Microsoft.Jet.OLEDB.4.0;Data Source='" + fichpath + fich + "';Extended Properties='Excel 8.0;HDR=Yes'"))
            {
                using (System.Data.OleDb.OleDbCommand ocmd = new System.Data.OleDb.OleDbCommand("", con))
                {
                    ocmd.Connection = con;
                    con.Open();
 
                    string sql = "CREATE TABLE [Errores] ( ";
                    bool flgcomma = true;
 
                    try
                    {
                        while (dr.Read())
                        {
                            switch (dr.GetString(1))
                            {
                                case "char":
                                    {
                                        sql += (flgcomma ? "" : ",") + dr.GetString(0) + " CHAR(1) ";
                                        flg = true;
                                        break;
                                    }
                                case "varchar":
                                    {
                                        sql += (flgcomma ? "" : ",") + dr.GetString(0) + " VARCHAR(250) ";
                                        flg = true;
                                        break;
                                    }
                                case "int":
                                    {
                                        sql += (flgcomma ? "" : ",") + dr.GetString(0) + " INT ";
                                        flg = true;
                                        break;
                                    }
                                case "datetime":
                                    {
                                        sql += (flgcomma ? "" : ",") + dr.GetDateTime(0) + " DATETIME ";
                                        flg = true;
                                        break;
                                    }
                            }
 
                            if (flg)
                            {
                                cols += (flgcomma ? "" : ",") + dr.GetString(0);
                                colstype += (flgcomma ? "" : ",") + dr.GetString(1);
                                flgcomma = false;
                            }
                            flg = false;
                        }
                    }
                    catch
                    { }
 
                    sql += ")";
                    ocmd.CommandText = sql;
                    ocmd.CommandType = CommandType.Text;
                    ocmd.ExecuteNonQuery();
                    con.Close();
                    cnx.Close();
 
                    cmd.CommandText = "SELECT " + cols + " FROM " + nombretabla + " WHERE FECHA_CARGA='" + fecha + "'";
                    cnx.Open();
                    SqlDataReader dr2 = cmd.ExecuteReader();
                    string[] s = cols.Split(',');
                    string[] st = colstype.Split(',');
                    int cant = s.Length;
                    con.Open();
 
                    while (dr2.Read())
                    { 
                        sql = "INSERT INTO [Errores] (" + cols + ") VALUES(";
                        flgcomma = true;
                        
                        for (int i = 0; i <= cant - 1; i++)
                        {
                            switch (st[i])
                            {
                                case "char":
                                    {
                                        try
                                        {
                                            string sv = dr2.GetString(i);
                                            sv = sv.Replace('\'', ' ').Replace('\"', ' ');
 
                                            sql += (flgcomma ? "'" : ",'") + dr2.GetString(i) + "'";
                                        }
                                        catch
                                        {
                                            sql += (flgcomma ? "'" : ",'") + "'";
                                        }
 
                                        flgcomma = false;
                                        break;
                                    }
                                case "varchar":
                                    {
                                        try
                                        {
                                            string sv = dr2.GetString(i);
                                            int y = 0;
                                            sv = sv.Replace('\'', ' ').Replace('\"', ' ');
 
                                            if (sv.Length > 250)
                                                sv = sv.Substring(1, 247) + "...";
 
                                            sql += (flgcomma ? "'" : ",'") + sv + "'";
                                        }
                                        catch
                                        {
                                            sql += (flgcomma ? "'" : ",'") + "'";
                                        }
 
                                        flgcomma = false;
                                        break;
                                    }
                                case "int":
                                    {
                                        try
                                        {
                                            sql += (flgcomma ? "" : ",") + dr2.GetInt32(i);
                                        }
                                        catch
                                        {
                                            sql += (flgcomma ? "" : ",") + "0";
                                        }
 
                                        flgcomma = false;
                                        break;
                                    }
                                case "datetime":
                                    {
                                        DateTime d = dr2.GetDateTime(i);
 
                                        try
                                        {
                                            sql += (flgcomma ? "'" : ",'") + d.Year.ToString() + (d.Month < 10 ? "0" : "") + d.Month.ToString() + (d.Day < 10 ? "0" : "") + d.Day.ToString() + "'";
                                        }
                                        catch
                                        {
                                            sql += (flgcomma ? "'" : ",'") + "'";
                                        }
 
                                        flgcomma = false;
                                        break;
                                    }
                            }
                        }
                        
                        sql += ")";
                        ocmd.CommandText = sql.Replace('\t',' ').Replace('\n',' ');
 
                        try
                        {
                            ocmd.ExecuteNonQuery();
                        }
                        catch
                        {
                            if (con.State == ConnectionState.Open)
                            {
                                ocmd.CommandText = "INSERT INTO [Errores] (" + cols.Substring(0, cols.IndexOf(',')) + ") VALUES('ERROR')";
                                ocmd.ExecuteNonQuery();
                            }
                        }
                    }
 
                    con.Close();
                    cnx.Close();
                }
            }
 
            //Insert Terminado
        }
        catch //(Exception ex)
        {
            //ex.ToString();
        }
 
        Response.Clear();
        Response.AddHeader("Content-Disposition", "attachment; filename=" + fich);
        Response.Charset = "";
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.ContentType = "application/excel";
        Response.TransmitFile(fichpath + fich);
        Response.End();
    }