mvtilborg

Got this now, but does not do anything, what is wrong? Any help is highly appreciated.

global $wpdb;
	// delete all posts WHERE meta_value = $aid;
	$wpdb->query("DELETE wp
		FROM $wpdb->posts wp
		LEFT JOIN $wpdb->postmeta pm ON pm.post_id = wp.ID
		WHERE mp.meta_key = 'product_aid' AND mp.meta_value = '". $aid ."'");
	// delete not used meta
	$wpdb->query("DELETE pm
		FROM $wpdb->postmeta pm
		LEFT JOIN $wpdb->posts wp ON wp.ID = pm.post_id
		WHERE wp.ID IS NULL");

Figured it out myself

global $wpdb;
		$querystr = "SELECT post_id, count(post_id)
			FROM $wpdb->postmeta
			WHERE
				(meta_key = 'product_aid' AND meta_value = '". $aid ."') OR
				(meta_key = 'product_id' AND meta_value = '". (string)$item->productID ."')
			GROUP BY post_id
			HAVING count(post_id) = 2;
		";
		$postid = $wpdb->get_var($wpdb->prepare($querystr));