如何使用PHP实现一个简单的数据导入导出功能

<?php
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "mydb";

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

// 使用PDO
try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch(PDOException $e)
{
    echo "连接失败: " . $e->getMessage();
}
?>

<?php
$sql = "SELECT * FROM mytable";
$result = $conn->query($sql);

$data = array();
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $data[] = $row;
    }
}
?>

<?php
$filename = "export.csv";
$file = fopen($filename, 'w');

// 写入表头
$header = array_keys($data[0]);
fputcsv($file, $header);

// 写入数据
foreach ($data as $row) {
    fputcsv($file, $row);
}

fclose($file);
?>

<form action="import.php" method="POST" enctype="multipart/form-data">
    <input type="file" name="file" />
    <input type="submit" value="导入" />
</form>

<?php
$target_dir = "/uploads/";
$target_file = $target_dir . basename($_FILES["file"]["name"]);
move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);

// 文件路径
$filepath = $target_dir . $_FILES["file"]["name"];
?>

<?php
$file = fopen($filepath, 'r');

// 跳过表头
fgetcsv($file);

// 插入数据
while (($line = fgetcsv($file)) !== false) {
    $sql = "INSERT INTO mytable (field1, field2, field3) VALUES ('$line[0]', '$line[1]', '$line[2]')";
    $conn->query($sql);
}

fclose($file);
?>