PDO multiple checkboxs inserting or delete

I need help to link between three tables by checkboxe:

features table ( id, title, sulg )

posts table (id, title, slug, added )

posts_features ( fea_id, post_id )

<input type="checkbox" name="featuresid[]" value="$features->id">

If checked ( insert ) if not exist.

foreach ($_POST['featuresid'] as $choice) {
$sql = $dbh->prepare("INSERT INTO posts_features (fea_id, post_id) VALUES ($choice, $id)");
$sql->execute();
}

if un-checked ( delete ) from posts_features

$sql = $dbh->prepare("delete form posts_features where ........

Thanks in advance.