PHP - Eliminar ciertos elementos de la bd asociados a otras cosas

<?php if(isset($_GET["product"]) && $_GET["product"]!=""):?>

	<?php

$products = BookData::getLike($_GET["product"]);

if(count($products)>0){

	?>

<h3>Resultados de la Busqueda</h3>

<table class="table table-bordered table-hover">

	<thead>

		<th>Código</th>

		<th>Nombre del Producto</th>

		<th>Solicitar</th>

	</thead>

	<?php

$products_in_cero=0;

	 foreach($products as $product):

	?>

	<tr>

		<td style="width:80px;"><?php echo $product->isbn; ?></td>

		<td><?php echo $product->title; ?></td>

		<td style="width:250px;"><form method="post" action="index.php?action=addtocart">

		<input type="hidden" name="book_id" value="<?php echo $product->id; ?>">

<?php $items = ItemData::getAvaiableByBookId($product->id);?>

<div class="input-group">

<select class="form-control" name="item_id" required>

	<option value=""> -- EJEMPLAR --</option>

	<?php foreach($items as $item):?>

	<option value="<?php echo $item->id; ?>"> <?php echo $item->code; ?></option>

	<?php endforeach; ?>

</select>

      <span class="input-group-btn">

		<button type="submit" class="btn btn-primary"><i class="glyphicon glyphicon-plus-sign"></i> Agregar</button>

      </span>

    </div>

		</form></td>

	</tr>

	<?php endforeach;?>

</table>

	<?php

}else{

	echo "<br><p class='alert alert-danger'>No se encontro el producto</p>";

}

?>

<hr><br>

<?php else:

?>

<?php endif; ?>