PHP - Php Form Prevent Empty Table Submit

<?php
// Parse the form data and add inventory item to the system

if (isset($_POST['product_name'])) {

    $product_name = $_POST['product_name'];
    $price = $_POST['price'];
    $category = $_POST['category'];
    $stock = $_POST['stock'];
    $details = $_POST['details'];
    $rating =$_POST['rating'];
    $letter = $_POST['letter'];
    $supplier = $_POST['supplier'];        

    // See if that product name is an identical match to another product in the system
    $sql = mysqli_query($con, "SELECT id FROM products WHERE product_name='$product_name' LIMIT 1");
    $productMatch = mysqli_num_rows($sql); // count the output amount
    //if product match is greater than 0
    if ($productMatch > 0) {
        echo 'Sorry you tried to place a duplicate "Product Name" into the system, <a href="inventory_list.php">click here</a>';
        exit();
    }
    // Add this product into the database now by sql query
    $sql = mysqli_query($con, "INSERT INTO products (product_name, price, details, category, stock, letter, supplier,  rating, date_added)
        VALUES('$product_name','$price','$details','$category', '$stock' ,'$letter',' $supplier' , '$rating' now())") or die (mysqli_error());        
     $pid = mysqli_insert_id($con);    
    // Place image in the folder
        $newname = "$pid.jpg";
        move_uploaded_file($_FILES['fileField']['tmp_name'], "../inventory_images/$newname"); //_FILES is a global var
    
    header("location: inventory_list.php"); //auto refresh, and it wont try to re add the item
    exit();//not necessary but its always safe to exit
}
?>

html form
<form action="inventory_list.php" enctype="multipart/form-data" name="myForm" id="myForm" method="post">
                <table width="95%" border="0" align="center" cellpadding="5" cellspacing="0" summary="this is where the admin will insert new items">
          <caption><div id="title"><a id="add_new_item"></a>Add New Inventory Item</div>
          </caption>
          <tr >
            <th width="30%" scope="col" align="left">Product Image</th>
            <th width="70%"><label class="desc">
            <input type="file" name="fileField" id="fileField"   autofocus required />
            </label></td>
          </tr>
          <tr >
            <th width="30%" scope="col" align="left">Product Name</th>
            <th width="70%" scope="col" align="left">
            <label class="desc">
                <input name="product_name" type="text" id="product_name" size="64"  autofocus required />
            </label></th>
          </tr>
          <tr>
            <th width="30%" scope="row" align="left">Letter</th>
            <td width="70%"> <label class="desc">
                <input name="letter" type="text" id="letter"  autofocus required />
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row" align="left">Product Price</th>
            <td width="70%"> <label class="desc">
                <input name="price" type="text" id="price"  autofocus required />
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row"align="left">Category</th>
            <td width="70%"><label class="desc">
            <select name="category" id="category">
            <option value="Fruits">Fruits</option>
            <option value="Vegetables">Vegetables</option>
            <option value="Indoor Plants">Indoor Plants</option>
            <option value="Outdoor Plants">Outdoor Plants</option>
            </select>
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row" align="left">Suppliers</th>
            <td width="70%"> <label class="desc">
            <select name="supplier" id="supplier">
            <option value="Kenny's Organic Supplies">Kenny's Organic Supplies</option>
            <option value="Mom's Garden">Mom's Garden</option>
            <option value="Big Brother">Big Brother</option>
            </select>
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row" align="left">Stock</th>
            <td width="70%"> <label class="desc">
                <input name="stock" type="text" id="stock"  autofocus required />
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row"align="left">Product Details</th>
            <td width="70%"><label class="desc">
            <textarea name="details" id="details" cols="35" rows="5"  autofocus required></textarea>
            </label></td>
          </tr>
              <tr>
            <th width="30%" scope="row" align="left">Rating</th>
            <td width="70%"><label class="desc">
            <select name="rating" id="rating" >
            <option value="1">1 of 3 Stars</option>
            <option value="2">2 of 3 Stars</option>
            <option value="3">3 of 3 Stars</option>
            </select>
            </label></td>
          </tr>

          <tr>
            <th width="30%" scope="row">&nbsp;</th>
            <td width="70%" align="right"><label class="desc">
            <input type="submit" name="button" id="button" value="Add This Item Now" />
            </label></td>
          </tr>
          <tr>
            <th width="30%" scope="row">&nbsp;</th>
            <td width="70%">&nbsp;</td>
          </tr>
      </table>
    </form>

Say I have an "Entries" table. I want to submit same multiple entries using a form submission. And If I have other queries submitted in the same form, I want those quarries to be submitted only once.  Is that possible to do? 

Here's my code.

if(isset($_POST['submit'])) {

  $entries = 10;

  $id   = 55;
  $name = 'Smith';

  $insert = $db->prepare("INSERT INTO entries(id, name) VALUES(:id, :name)");
  $insert->bindParam(':id', $id);
  $insert->bindParam(':name', $name);
  $result_insert = $insert->execute();
  if($result_insert == false) {
    echo 'Fail';
  } else {
    echo 'Success';
  }

}
?>
<form action="" method="post">
  <input type="submit" name="submit" value="SUBMIT" />
</form>