CRUD中的UPDATE问题

Question

我是php的新手，我制作了一个简单的CRUD应用。不幸的是，我遇到了这个问题，我不知道update.php中的代码出了什么问题。当我单击index.php中的update时，它的未定义变量。我认为我的形式价值是错误的。任何帮助表示赞赏。 update.php

<?php
include("connection.php");

if (isset($_POST['customerNumber'])) {
    $customerNumber = $_POST['customerNumber'];

    $q  = "SELECT customerNumber, checkNumber, paymentDate, amount FROM payments WHERE customerNumber='$customerNumber'";
    $rq = mysqli_query($conn, $q);

    while ($row = mysqli_feth_assoc($rq)) {
    $customerNumber = $row['customerNumber'];
    $checkNumber    = $row['checkNumber'];
    $paymentDate    = $row['paymentDate'];
    $amount         = $row['amount'];
    }
}
?>
    <!-- from the index.php update -->
<form action="update.php?customerNumber=$customerNumber" method="post">
    <label>
        <input type="text" name="customerNumber" value="<?php echo $row['customerNumber']; ?>" placeholder="Customer Number" required>
    </label>
    <label>
        <input type="text" name="checkNumber" value="<?php echo $row['checkNumber']; ?>"  placeholder="Check Number" required>
    </label>
    <label>
        <input type="text" name="paymentDate" value="<?php echo $row['paymentDate']; ?>" placeholder="Payment Date" required>
    </label>
    <label>
        <input type="number" name="amount" value="<?php echo $row['amount']; ?>"  placeholder="Amount">
    </label>
    <input type="submit" name="submit" value="update">
</form>
<?php
    include('connection.php');
if (isset($_POST['submit'])) {
    $customerNumber = $_POST['customerNumber'];
    $checkNumber    = $_POST['checkNumber'];
    $paymentDate    = $_POST['paymentDate'];
    $amount         = $_POST['amount'];

    $q = "UPDATE payments SET customerNumber='$customerNumber', checkNumber='$checkNumber', paymentDate='$paymentDate', amount='$amount' WHERE customerNumber='$customerNumber' ";

    $rq = mysqli_query($conn, $q);

    if($rq){
        header('Location: index.php');
    }else{
        echo "Something went wrong";
    }
}
    ?>