PHP Excel导出仅显示MYsql表的最后一行

<?php
// 连接到MySQL数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 查询MySQL表的数据
$sql = "SELECT * FROM your_table ORDER BY id DESC LIMIT 1";
$result = $conn->query($sql);

// 导出为Excel文件
require_once 'PHPExcel/PHPExcel.php';

$objPHPExcel = new PHPExcel();
$objPHPExcel->getActiveSheet()->setTitle('Sheet1');

$row = 1;
while ($row_data = $result->fetch_assoc()) {
    $col = 0;
    foreach ($row_data as $value) {
        $objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow($col, $row, $value);
        $col++;
    }
    $row++;
}

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter->save('output.xlsx');

// 关闭数据库连接
$conn->close();
?>