大家好，我有下面的代码，但当我点击生成的链接时，一个新页面打开，上面显示0。我做错了什么？

function list_reservation_to_csv() {

 global $wpdb;
 $table_name = $wpdb->prefix . \'prenotazione_eventi\';
 $file = \'email_csv\'; // ?? not defined in original code
 $results = $wpdb->get_results("SELECT * FROM $table_name",ARRAY_A);

 if (empty($results)) {
   return;
 }

 $csv_output = \'"\'.implode(\'";"\',array_keys($results[0])).\'";\'."\\n";;

 foreach ($results as $row) {
  $csv_output .= \'"\'.implode(\'";"\',$row).\'";\'."\\n";
 }
 $csv_output .= "\\n";

 $filename = $file."_".date("Y-m-d_H-i",time());
 header("Content-type: application/vnd.ms-excel");
 header("Content-disposition: csv" . date("Y-m-d") . ".csv");
 header( "Content-disposition: filename=".$filename.".csv");
 print $csv_output;
 exit;

 }
add_action(\'wp_ajax_csv_pull\',\'list_reservation_to_csv\');

$ajax_url = admin_url(\'admin-ajax.php?action=csv_pull\');

<a href="<?php echo $ajax_url; ?>"><button>Scarica csv</button></a>