PHP - выпадающие списки становятся пустыми после ошибки

У меня есть файл php с именем «add_order.php». Требуется три ввода, два ввода (Магазин и Покупатель) поступают из выбора двух соответствующих раскрывающихся списков, а последний ввод (Дата) поступает из ручного ввода пользователя. Если дата остается пустой при отправке, страница выдает ошибку и снова отображает поля ввода под сообщением об ошибке, чтобы пользователи могли повторить ввод. Однако в этом случае два раскрывающихся списка становятся пустыми. Кто-нибудь может помочь? Спасибо.

     <?php # add_order.php

     $page_title = 'Add Order';

     include ('mysqli_connect.php');

     // Check if the form has been submitted.
     if (isset($_POST['submitted'])) {

    $errors = array(); // Initialize error array.

    // Check for a customer.
    if (empty($_POST['Customer_ID'])) {
        $errors[] = 'You forgot to enter the customer of the order.';
    } else {
        $customer_id = $_POST['Customer_ID'];

        $query = "SELECT * FROM customers WHERE Customer_ID=$customer_id ORDER BY Last_N ASC";
        $result = @mysqli_query ($dbc, $query);
        while ($row = mysqli_fetch_array($result, MYSQL_ASSOC))
        {
        $customer_name=$row['First_N'].' '.$row['Last_N'];
        }
           }

    // Check for a director ID.
    if (empty($_POST['Store_ID'])) {
        $errors[] = 'You forgot to enter the store of the order.';
    } else {
        $store_id = $_POST['Store_ID'];

        $query = "SELECT * FROM store WHERE Store_ID=$store_id ORDER BY Store_Name ASC";
        $result = @mysqli_query ($dbc, $query);
        while ($row = mysqli_fetch_array($result, MYSQL_ASSOC))
        {
        $store_name=$row['Store_Name'];
        }
           }


    // Check for the date of order.
    if (empty($_POST['Order_Date'])) {
        $errors[] = 'You forgot to enter the date of order.';
    } else {
        $order_date = $_POST['Order_Date'];
           }



    if (empty($errors)) { // If everything's okay.

        // Add the order to the database.

        // Make the query.
        $query = "INSERT INTO prescription_orders (Customer_ID, Order_Date, Store_ID) VALUES ('$customer_id', '$order_date', '$store_id')";     
        $result = @mysqli_query ($dbc, $query); // Run the query.
        if ($result) { // If it ran OK.

            // Print a message.
            echo '<h1 id = "mainhead">Success!</h1>
        <p>You have added:</p>';

           echo "<table>
        <tr><td>Customer_ID:</td><td>{$customer_id}</td></tr>
        <tr><td>Order_Date:</td><td>{$order_date}</td></tr>
        <tr><td>Store_ID:</td><td>{$store_id}</td></tr>

        </table>";

        $order_id = mysqli_insert_id($dbc); // Retrieve the id number of the newly added record
        echo'<a href = "http://localhost/cvs/add_order_item.php?id=' . $order_id . '">Add a item to this order</a>';
        exit();

        } else { // If it did not run OK.
            echo '<h1 id = "mainhead">System Error</h1>
            <p class = "error">The movie could not be added due to a system error. We apologize for any inconvenience.</p>'; // Public message.
            echo '<p>' . mysqli_error($dbc) . '<br /><br />Query: ' . $query . '</p>'; // Debugging message.
            exit();
        }

    } else { // Report the errors.

        echo '<h1 id = "mainhead">Error!</h1>
        <p class = "error">The following error(s) occurred:<br />';
        foreach ($errors as $msg) { // Print each error.
            echo " - $msg<br />\n";
        }
        echo '</p><p>Please try again.</p><p><br /></p>';

    } // End of if (empty($errors)) IF.


    mysqli_close($dbc); // Close the database connection.

     } // End of the main Submit conditional.
     ?>







     <?php 
      if (isset($_POST['Customer_ID'])) $this_customer_id=$_POST['Customer_ID'];
      if (isset($_POST['Store_ID'])) $this_store_id=$_POST['Store_ID'];
     ?>
     <h2>Add Order</h2>
     <form action = "add_order.php" method = "post">

     <p>Store: <select name = "Store_ID">
     <?php 
     // Build the query
     $query = "SELECT * FROM store ORDER BY Store_Name ASC";
     $result = @mysqli_query ($dbc, $query);
     while ($row = mysqli_fetch_array($result, MYSQL_ASSOC))
     {

     if ($row['Store_ID'] == $this_store_id) {
     echo '<option value = "'.$row['Store_ID'].'"                
     selected = "selected">'.$row['Store_Name'].'</option>';
     }
     else {
     echo'<option                
     value = "'.$row['Store_ID'].'">'.$row['Store_Name'].'</option>';}

     }
     ?>
     </select>&nbsp;&nbsp;&nbsp;<a href = "add_store.php">Add a new Store</a>
     </p>
    <p>Customer: <select name = "Customer_ID">
     <?php 
     // Build the query
     $query = "SELECT * FROM customers ORDER BY Last_N ASC";
     $result = @mysqli_query ($dbc, $query);
     while ($row = mysqli_fetch_array($result, MYSQL_ASSOC))
     {

     if ($row['Customer_ID'] == $this_customer_id) {
     echo '<option value = "'.$row['Customer_ID'].'" 
     selected = "selected">'.$row['First_N'].' '.$row['Last_N'].'</option>';
     }
      else {
     echo'<option value = "'.$row['Customer_ID'].'">'.$row['First_N'].' 
     '.$row['Last_N'].'</option>';}

     }
     ?>
     </select>&nbsp;&nbsp;&nbsp;<a href = "add_customer.php">Add a new 
     Customer</a>
     </p>
     <p>Date of Order: <input type = "text" name = "Order_Date" size = "10" 
     maxlength = "10" value = "<?php if (isset($_POST['Order_Date'])) echo 
     $_POST['Order_Date']; ?>" />&nbsp;<i>YYYY-MM-DD</i></p>
    <p><input type = "submit" name = "submit" value = "Add Order" /></p>
    <input type = "hidden" name = "submitted" value = "TRUE" />
     </form>
     <a href = "index.php">Go back to Index Page</a>