Error Showing a data

Good to know how to solve this error:

Fatal error: Uncaught Error: Call to a member function fetch_array() on boolean in C:\xampp\htdocs\Horarios\paginas\actualizarsubjects.php:12 
Stack trace: #0 {main} thrown in C:\xampp\htdocs\Horarios\paginas\actualizarsubjects.php on line 12

and that is simply that I want to take data from one form to another in different pages my main key in the database is varchar , when bringing them if I only write numbers shows them but, if I write letters and numbers As I want, I get that error, I appreciate your help.

<?php
session_start();
require_once "../php/connect.php";
if(!$_SESSION['verificar']){
//
}
else {
require_once "../php/connect.php";
    $usu =$_GET['codigomateria'];
    $query="SELECT codigomateria,creditos,nombre FROM materias WHERE codigomateria=".$usu;
    $consulta1=$mysqli->query($query);
    while($fila=$consulta1->fetch_array(MYSQLI_ASSOC)){
  $codigomateria=$fila['codigomateria'];
  $nombre=$fila['nombre'];
  $creditos=$fila['creditos'];
}
}
echo $_SESSION['user'];

? >