paad/action/action_materias.php

<?php
$ruta = "../";
require_once "../class/c_login.php";

extract($_POST);
# print_r($_POST); exit;

if (!isset($_SESSION['user']))
    die(header('Location: index.php'));

$user = unserialize($_SESSION['user']);

if (!$user->admin && ($access = $user->access('asistencia')) == 'n')
    die(json_encode(['error' => true]));

$user->print_to_log('Consultar materias');
$materias = queryAll(
    "SELECT id, nombre FROM FS_MATERIA WHERE carrera = COALESCE(:carrera, carrera) ORDER BY nombre",
    [':carrera' => empty($carrera) ? null : $carrera]
);
?>

<?= json_encode([
    'status' => 'success',
    'materias' => $materias,
]); ?>