如何在PHP下拉列表中实现MYSQL数据库到excel转换时字符串限制的扩展

<?php
// 导出数据到Excel
require_once 'PHPExcel/PHPExcel.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);
}

// 选择要导出的数据表
$table = "your_table_name";

// 查询要导出的数据
$sql = "SELECT * FROM $table";
$result = $conn->query($sql);

// 创建PHPExcel对象
$objPHPExcel = new PHPExcel();

// 设置Excel属性
$objPHPExcel->getProperties()->setCreator("Your Name")
                             ->setLastModifiedBy("Your Name")
                             ->setTitle("Export Data")
                             ->setSubject("Data")
                             ->setDescription("Data export")
                             ->setKeywords("excel")
                             ->setCategory("Data");

// 创建工作表
$objPHPExcel->setActiveSheetIndex(0);
$sheet = $objPHPExcel->getActiveSheet();

// 设置表头
$sheet->setCellValue('A1', 'Column 1');
$sheet->setCellValue('B1', 'Column 2');
$sheet->setCellValue('C1', 'Column 3');

// 遍历查询结果，写入Excel文件
$row = 2;
while ($row_data = $result->fetch_assoc()) {
    $col = 0;
    foreach ($row_data as $value) {
        // 限制字符串长度为10，并自动换行
        $sheet->setCellValueExplicitByColumnAndRow($col, $row, $value, PHPExcel_Cell_DataType::TYPE_STRING, null, true);
        $col++;
    }
    $row++;
}

// 保存Excel文件
$filename = "export.xlsx";
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter->save($filename);

echo "导出成功！";
?>