Fatal error: Uncaught Error: Call to undefined function mysql_query() in C:\xampp\szkola\ksiazki.php:20 Stack trace: #0 C:\xampp\szkola\index.php(88): require_once() #1 C:\xampp\htdocs\zsz2\index.php(8): require_once('C:\\xampp\\szkola...') #2 {main} thrown in C:\xampp\szkola\ksiazki.php on line 20