好的，所以我正在尝试制作一个安全的下载系统，其中具有特定许可证号的某个购买者可以访问下载，在他的许可被取消之前他可以下载两次。为了做到这一点，我在同一行中的“product_id”和“license_number”列旁边有一个“count”列。当我的 paypal ipn 脚本确认时，产品 ID 和许可证号会自动生成并传递给买家。
现在问题来了：当他们使用正确的变量访问下载页面时，计数会更新 +1，但由于某种原因，这个 sql 查询运行了两次，实际上我的数据库中得到了 +2。我已经对其进行了一些更改以首先检查该值，然后进行相应更改（以查看是否修复了错误），但错误仍未修复。
我个人认为，也许我调用文件下载会使脚本运行两次，还是我错了？
这是代码：
<?php
include ('../storescripts/connect_to_mysql.php');
// Looks first if the post variables have been set
if(!isset($_GET['id']) && ($_GET['lcn'])){
// Error output
echo 'The big PHP monster will not accept you into his cave without bringing an offering of variables!';
} else {
// Set the variables
$id = $_GET['id'];
$license_number = $_GET['lcn'];
// Check if there is such a thing (Yes, aliens) as the given id and license number
$sql = mysql_query("SELECT * FROM secure_downloads WHERE product_id ='$id' AND license_number ='$license_number' LIMIT 1");
$result = mysql_num_rows($sql);
if($result > 0){
// Now update the download count
// Check first if the count is 0
// Make a variable from the count sql
$sql_count = mysql_query("SELECT * FROM secure_downloads WHERE product_id='$id' AND license_number='$license_number' LIMIT 1");
while($row = mysql_fetch_assoc($sql_count)){
$count = $row['count'];
}
// Check if the count is above two
if ($count >= 2){
// Download has already been downloaded 2 times, do not allow download
echo 'The download limit for this file has been reached.';
exit();
} else if ($count = 0) {
// Everything is alright, start downloading
// Force the file download
$file = 'test.jpg';
// Change the count to 1
mysql_query("UPDATE secure_downloads SET count=1 WHERE product_id = '$id' AND license_number = '$license_number'");
readfile($file);
exit();
} else if ($count = 1) {
// Everything is alright, start downloading
// Force the file download
$file = 'test.jpg';
// Change the count to 2
mysql_query("UPDATE secure_downloads SET count=2 WHERE product_id = '$id' AND license_number = '$license_number'");
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($file));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
ob_clean();
flush();
readfile($file);
exit();
}
} else {
// It doesn't exist, tell the user either the variables were wrong or the
// download limit has been reached
echo 'Cannot download the file, either the link is wrong or the download limit has been reached';
}
}
?>