Проблема codigo PHP Session

Question

У меня есть форма, которая передает идентификатор, который необходимо записать в сеанс.
Он не изменяется.$id = $ _SESSION ['id']; // this is the error line:

Примечание: неопределенный индекс: id в C: \ wamp \ www \ project \ database \ update.php в строке 5

editar.php

    <?php
        include_once 'banco_de_dados/conexao.php';          
        $id = filter_input(INPUT_GET, 'id', FILTER_SANITIZE_NUMBER_INT);
        $_SESSION['id'] = $id;
        $querySelect = $link->query("select * from tb_clientes where id='$id'");            
        while($registros = $querySelect->fetch_assoc()):
            $nome = $registros['nome'];
            $email = $registros['email'];
            $telefone = $registros['telefone'];
        endwhile;
        ?>
        <!-- Formulário de Cadastro-->  
            <p>&nbsp;</p>
        <form action="banco_de_dados/update.php" method="post" class="col s12">
            <fieldset class="formulario" style="padding:15px;">
                <legend><img src="assets/img/logo.png"></legend>
                <h5 class="light center">Alteração de Clientes</h5>         
                <!-- Campo Nome -->
                <div class="input-field col s12">
                    <i class="material-icons prefix">account_circle</i>
                    <input type="text" name="nome" id="nome" value="<?php echo $nome ?>" maxlength="40" required autofocus>
                    <label for="nome">Nome do Cliente</label>
                </div>              
                <!-- Campo Email -->
                <div class="input-field col s12">
                    <i class="material-icons prefix">email</i>
                    <input type="email" name="email" id="email" value="<?php echo $email ?>" maxlength="50" required autofocus>
                    <label for="email">Email do Cliente</label>
                </div>              
                <!-- Campo Telefone -->
                <div class="input-field col s12">
                    <i class="material-icons prefix">phone</i>
                    <input type="tel" name="telefone" id="telefone" value="<?php echo $telefone ?>" maxlength="15" required autofocus>
                    <label for="telefone">Telefone do Cliente</label>
                </div>              
                <!-- Botoes -->
                <div class="input-field col s12">
                    <input type="submit" value="alterar" class="btn blue">
                    <a href="consultas.php" class="btn red">cancelar</a>
                </div>
            </fieldset>
        </form>
    </div>

update.php

        <?php
        session_start();
        include_once 'conexao.php'; 
        $id = $_SESSION['id']; // essa é a linha do erro
        $nome = filter_input(INPUT_POST, 'nome', FILTER_SANITIZE_SPECIAL_CHARS);
        $email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
        $telefone = filter_input(INPUT_POST, 'telefone', FILTER_SANITIZE_NUMBER_INT);
        $queryUpdate = $link->query("update tb_clientes set nome='$nome', email='$email', telefone='$telefone' where id='$id'");
        $affected_rows = mysqli_affected_rows($link);
        if($affected_rows > 0):
            header("Location:../consultas.php");
        endif;