Fatal error: Uncaught ValueError: mysqli::query(): Argument #1 ($query) cannot be empty in /var/www/vhost/wydawnictwo.ue.poznan.pl/exp_eksportxls.php:18 Stack trace: #0 /var/www/vhost/wydawnictwo.ue.poznan.pl/exp_eksportxls.php(18): mysqli->query('') #1 {main} thrown in /var/www/vhost/wydawnictwo.ue.poznan.pl/exp_eksportxls.php on line 18