检查此代码，您应该将文件地址添加到DB

<?php
    // get id to search on DB and get detail
    $id = $_REQUEST['id'];

    try {
        $conn = new PDO("pgsql:host=$host;port=5432;dbname=$dbname", $username, $password);
        // set the PDO error mode to exception
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        //echo "Connected successfully";
    } catch(PDOException $e) {
        echo "Connection failed: " . $e->getMessage();
    }

    $stmt = $conn->prepare("SELECT url FROM mytable WHERE id=? LIMIT 1"); 
    $stmt->execute([$id]); 
    $row = $stmt->fetch();
    // the address of file in server 
    $path = $row['url'];

    if (file_exists($path) && is_readable($path)) {
        // get the file size and send the http headers
        $size = filesize($path);
        header('Content-Type: application/octet-stream'); 
        header('Content-Length: '.$size);
        header('Content-Disposition: attachment; filename='.$filename);
        header('Content-Transfer-Encoding: binary');
        // open the file in binary read-only mode
        // display the error messages if the file can´t be opened
        $file = @ fopen($path, 'rb');
        if ($file) {
        // stream the file and exit the script when complete
            fpassthru($file);
            exit;
        } else {
            echo $err;
        }
    } else {
        echo 'check that file exists and is readable';;
    }

    ?>