$sql="DELETE FROM product_types WHERE id=".$_POST['type_id'];
if(!mysqli_query($conn,$sql)){
    echo "This type can't be deleted because it belongs to other products."; exit();
}else {logging($target_name,"delete");}

$sql="DELETE FROM product_types WHERE id=".$_POST['type_id'];
$result=mysqli_query($conn,$sql)
if(!$result){
    echo "This type can't be deleted because it belongs to other products."; exit();
}else {logging($target_name,"delete");}