如何使用php mysqli创建下载文件数

$servername = "数据库服务器地址";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

$filename = $_GET['filename']; // 从URL参数获取要下载的文件名
$file_path = '文件存储路径' . $filename; // 文件的完整路径

if (file_exists($file_path)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename=' . basename($file_path));
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file_path));
    ob_clean();
    flush();
    readfile($file_path);
    exit;
} else {
    echo '文件不存在。';
}

CREATE TABLE files (
    id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    filename VARCHAR(100) NOT NULL,
    filesize INT(6) UNSIGNED NOT NULL,
    upload_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

$filename = $_FILES['file']['name']; // 从上传表单获取文件名
$filesize = $_FILES['file']['size']; // 从上传表单获取文件大小

$sql = "INSERT INTO files (filename, filesize) VALUES ('$filename', $filesize)";

if ($conn->query($sql) === TRUE) {
    echo '文件上传成功。';
} else {
    echo '文件上传失败：' . $conn->error;
}

<a href="download.php?filename=example.txt">点击下载文件</a>