使用PHP POST从MYSQL下载CSV文件

Question

I am unable to create a script to download a CSV file. every time I run the script it breaks. I am not receiving any errors. The page just stops loading once it gets to the script. I have looked around and found some answers but none of them seem to be working. I am new to php, and would greatly appreciate an explanation if you know whats going on here. Thanks in advance!

if (isset($_POST['downloadCSV'])) {

$list = null;
include 'classes/Credentials.php';

try     
 {
 // Include globals from credentials.
 global $dbname, $host, $user, $pass;

// Set up on database switch
$conn = new PDO("mysql:dbname=$dbname;host=$host", $user, $pass);
$conn->exec("SET CHARACTER SET utf8");


        } catch(PDOException $e) {
            echo $e->getMessage();
                                }

 // Define and perform the SQL SELECT query
  $sql = 'SELECT * FROM rental';
  $result = $conn->query($sql);

 // If the SQL query is succesfully performed ($result not false)
  if($result !== false) 
  {
    $num_fields = mysql_num_fields($result);
    $headers = array();

    for ($i = 0; $i < $num_fields; $i++) {
    $headers[] = mysql_field_name($result , $i);             
    $fp = fopen('php://output', 'w');

    if ($fp && $result) {
        header('Content-Type: text/csv');
        header('Content-Disposition: attachment; filename="export.csv"');
        header('Pragma: no-cache');
        header('Expires: 0');
        fputcsv($fp, $headers);

        while ($row = $result->fetch_array(MYSQLI_NUM)) {
        fputcsv($fp, array_values($row));
        }

        $conn = null;        // Disconnect
        die;
    }
   }
 }
}

Answer 1

Try

// If the SQL query is succesfully performed ($result not false)
if($result != false) {

The comparison operator you are using is checking for 'not identical' and not 'not equal'