kenapa data yang diedit lalu kemudian disimpan tidak terjadi perubahan di tabel . ini script yang saya gunakan: ini pada file proses.php*

} else if (isset($_POST['edit'])) {
$id = $_POST['id'];
$nama = trim(mysqli_real_escape_string($con, $_POST['nama']));
$no_telp = trim(mysqli_real_escape_string($con, $_POST['no_telp']));
$asal_instansi = trim(mysqli_real_escape_string($con, $_POST['asal_instansi']));
$jurusan = trim(mysqli_real_escape_string($con, $_POST['jurusan']));
$waktu_mulai = trim(mysqli_real_escape_string($con, $_POST['waktu_mulai']));
$waktu_akhir = trim(mysqli_real_escape_string($con, $_POST['waktu_akhir']));
mysqli_query($con, "UPDATE datapkl SET nama = '$nama', no_telp = '$no_telp', asal_instansi = '$asal_instansi', jurusan = '$jurusan', waktu_mulai = '$waktu_mulai', waktu_akhir = '$waktu_akhir' WHERE id_pkl = 'id'") or die (mysqli_error($con));
echo "<script>window.location='data.php';</script>";
}
?>

ini pada file edit.php

<?php
$id = @$_GET['id'];
$sql_pkl = mysqli_query($con, &quot;SELECT * FROM datapkl WHERE id_pkl = '$id'&quot;) or die (mysqli_error($con));
$data = mysqli_fetch_array($sql_pkl);
?>
<form action="proses.php" method="post">
                <div class="form-group">
                    <label for="nama">Nama Lengkap</label>
                    <input type="hidden" name="id" value="<?=$data['id_pkl']?>">
                    <input type="text" name="nama" id="nama" value="<?=$data['nama']?>" class="form-control" required autofocus>
                </div>
                <div class="form-group">
                    <label for="no_telp">No.Telepon</label>
                    <input type="text" name="no_telp" id="no_telp" value="<?=$data['no_telp']?>" class="form-control" required autofocus>
                </div>
                <div class="form-group">
                    <label for="asal_instansi">Asal Instansi</label>
                    <input type="text" name="asal_instansi" id="asal_instansi" value="<?=$data['asal_instansi']?>" class="form-control" required autofocus>
                </div>
                <div class="form-group">
                    <label for="jurusan">Jurusan</label>
                    <input type="text" name="jurusan" id="jurusan" value="<?=$data['jurusan']?>" class="form-control" required autofocus>
                </div>
                <div class="form-group">
                    <label for="waktu_mulai">Waktu Mulai</label>
                    <input type="date" name="waktu_mulai" id="waktu_mulai" value="<?=$data['waktu_mulai']?>" class="form-control" required autofocus>
                </div>
                <div class="form-group">
                    <label for="waktu_akhir">Waktu Akhir</label>
                    <input type="date" name="waktu_akhir" id="waktu_akhir" value="<?=$data['waktu_akhir']?>"class="form-control" required autofocus>
                </div>
                <div class="form-group pull-right">
                    <input type="submit" name="edit" value="Simpan" class="btn btn-success">
                </div>
            </form>
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