PHP: Writing a MYSQL query to CSV

Question

I'm attempting to write a MySQLi query to a downloadable CSV. The following headers open a stream for the CSV:

$fileName = ''; //empty file name, file name is cast later
header("Cache=Control: must-revalidate, post-check=0, pre-check=0");
header('Content-Description: File Transfer');
header("Content-type: text/csv");
header("Content-Disposition: attachment; filename={$fileName}");
header("Expires: 0");
header("Pragma: public");
$fh = @fopen( 'php://output', 'w' );

Below this I have the following which attempts to query and cast each row of the query to a new line in a CSV file:

if(isset($_POST["Submit"]) && ($_POST['Weight'] == 'Weight')){
    $fileName .= 'OutputWeightNull.csv';
    $query = mysqli_query($conn, 'SELECT * FROM  `Some_Table` WHERE WEIGHT = 0 OR weight IS NULL')or die(mysql_error());
    $result = mysqli_fetch_array($query) or die(mysql_error());
    $headerDisplayed = false;
    foreach ($result as $data){
    if (!headerDisplayed){
    fputcsv($fh, array_keys());
    $headerDisplayed = true;
        }
        fputcsv($fh, $data);
    }
}

The CSV is downloading to the browser as desired, however it's appearing empty, the query results are not being sent to the CSV. Could anyone point me in the right direction as to why this might be.

This is my my first attempt at a PHP script more complex that the hello world. Apologies if the answers are very simple or obvious.

Answer 1

Try like this

if(isset($_POST["Submit"]) && ($_POST['Weight'] == 'Weight')){
 $fileName = 'OutputWeightNull.csv';
 $fh = @fopen( 'php://output', 'w' );
 header("Cache=Control: must-revalidate, post-check=0, pre-check=0");
 header('Content-Description: File Transfer');
 header("Content-type: text/csv");
 header("Content-Disposition: attachment; filename={$fileName}");
 header("Expires: 0");
 header("Pragma: public");

 $query = mysqli_query($conn, 'SELECT * FROM  `Some_Table` WHERE WEIGHT = 0 OR weight IS NULL')or die(mysql_error());
 $headerDisplayed = false;
 while($result = mysqli_fetch_array($query, MYSQLI_ASSOC)) {  
  if (!$headerDisplayed){
   fputcsv($fh, array_keys($result));
   $headerDisplayed = true;
  }
  fputcsv($fh, $result);
 }
}

you need to place the csv header inside 'if' loop