SQL & PL/SQL

I have a tree represented in the DB (think more folder hiea than a tree, no concept of left node right node).

Some of the nested folders are orphaned so I need to find them and delete them.

Two tables support this like:

table name: folders
column: id
column: folder_name
column: type (can be of type 'root' or 'folder')

table name: parent_child
column: parent_id <= is a folder.id
column: child_id <= is a folder.id

To find the level 1 folders that are orphaned, I can do:

$select * from folders f where type='folder' and id not in (select parent_id from parent_child);

this is the first level folders that are orphaned. These also have children (with constraints).

so I need to get a list of the first level folders that are orphaned and delete from the leaf
nodes up to the folder that is orphaned.

Is this possible to do?

---
Visual:
- root1
- folder1a <= hiearchy of folders
- root2 <= this root should exist but does not so no entry in 'parent_child' for all children
- folder2a
- folder2b <= should exist but does not, so no entry in 'parent_child' for all children
- folder2ba <= this folder and all children should be deleted
- folder2baa
- folder2bab
- folder2bac
- folder2bb <= this folder and all children should be deleted
- folder2bc <= this folder and all children should be deleted
- folder2c
- root3 <= hiearchy of folders