当我点击导出到Excel时，如何设置CardNum的文本值

if(isset($_POST["export_excel"])) { $sql = "SELECT tract1,CardNum,tract2,tract3 FROM exceldata a LEFT JOIN tblcardnum b on a.EXID =b.EXID "; $result = mysqli_query($connect, $sql); if(mysqli_num_rows($result) > 0) { $output .= ' <table class="table" bordered="1"> <tr> <th>Id</th> <th>First Name</th> <th>Last Name</th> </tr> '; while($row = mysqli_fetch_array($result)) { $output .= ' <tr> <td>'.$row["tract1"].'</td> <td>'.$row["CardNum"].'</td> <td>'.$row["tract2"].'</td> </tr> '; } $output .= '</table>'; header("Content-Type: application/xls"); header("Content-Disposition: attachment; filename=download.xls"); echo $output; } }