A help with a hierarchical query

Question

I've got two tables:
FOLDERS where relevant fields are: folderId, parentFolderId, folderQuota
and DOCUMENTS where the relevant fields are: folderId, size
FOLDERS is hierarchical - parentFolderId of a child's folder is set to folderId of the parent
folderQuota is nullable (quota not set)
Now, I need to execute a query with the following recursive logic
<i>function calcQuota (folderIdpar, isFirstpar) {
if (not isFirstpar) and (folderQuota of folder with folderIdpar is not null) return folderQuota;
return size of all documents where folderId = folderIdpar + calcQuota (folderId of all children, false);
}</i>
(I hope the pseudocode is understandable - the query is executed as <i>calcQuota(originalFolderId, true)</i>).
Now, my question is if I can achieve it with a single hierarchical query, or if I have to implement it as a recursive stored procedure.
Thanks!
P.S. I'm using Oracle XE (10g)

Answer 1

OK,
I will need to create it (in real life it is created by an application), so I hope I will make it correct. If not, it should be easy to fix.
create table folders (
folder_id number primary key
parent_folder_id number,
quota number
create table documents (
document_id number primary key
folder_id number,
size number
INSERT INTO folders (folder_id, quota) VALUES (1, 1);
INSERT INTO folders (folder_id, parent_folder_id, quota) VALUES (2, 1, 2);
INSERT INTO folders (folder_id, parent_folder_id) VALUES (3, 1);
INSERT INTO folders (folder_id, parent_folder_id, quota) VALUES (4, 2, 4);
INSERT INTO folders (folder_id, parent_folder_id) VALUES (5, 2);
INSERT INTO folders (folder_id, parent_folder_id, quota) VALUES (6, 3, 8);
INSERT INTO folders (folder_id, parent_folder_id) VALUES (7, 3);
INSERT INTO documents (document_id, folder_id, size) VALUES (1, 1, 16);
INSERT INTO documents (document_id, folder_id, size) VALUES (2, 2, 32);
INSERT INTO documents (document_id, folder_id, size) VALUES (3, 3, 64);
INSERT INTO documents (document_id, folder_id, size) VALUES (4, 3, 128);
INSERT INTO documents (document_id, folder_id, size) VALUES (5, 4, 256);
INSERT INTO documents (document_id, folder_id, size) VALUES (6, 5, 512);
INSERT INTO documents (document_id, folder_id, size) VALUES (7, 6, 1024);
INSERT INTO documents (document_id, folder_id, size) VALUES (8, 7, 2048);
running the query for folder_id = 1 should return 1 + 2 + 64 + 128 + 8 + 2048 = 2251
running the query for folder_id = 2 should return 4 + 512 = 516
I have decided for this data, because it allows to track what values (folder.quota or document.size) is included in the result.
(it is the knapsack problem - see http://en.wikipedia.org/wiki/Knapsack_problem)
P.S. I'm leaving for three weeks, so I will come back after that.