This is an example on how to compute a rollup sum over a hierarchy.

rollup_sum.sql

CREATE TABLE
  t_folders (
    id INTEGER, 
    parent_id INTEGER, 
    name VARCHAR2(100) 
  );

CREATE TABLE
  t_files (
    id INTEGER, 
    folder_id INTEGER, 
    name VARCHAR2(100), 
    weight NUMBER
  );

INSERT INTO t_folders(id, parent_id, name) VALUES (0, NULL, 'Folder #0');
INSERT INTO t_folders(id, parent_id, name) VALUES (1, 0, 'Folder #1');
INSERT INTO t_folders(id, parent_id, name) VALUES (2, 0, 'Folder #2');
INSERT INTO t_folders(id, parent_id, name) VALUES (3, 1, 'Folder #3');
INSERT INTO t_folders(id, parent_id, name) VALUES (4, 1, 'Folder #4');
INSERT INTO t_folders(id, parent_id, name) VALUES (5, 2, 'Folder #5');
INSERT INTO t_folders(id, parent_id, name) VALUES (6, 2, 'Folder #6');
COMMIT;

INSERT INTO t_files(id, folder_id, name, weight) VALUES (7, 5, 'File #1', 10);
INSERT INTO t_files(id, folder_id, name, weight) VALUES (8, 2, 'File #2', 13);
COMMIT;

SELECT 
  SYS_CONNECT_BY_PATH(f.name, '/') path, 
  CONNECT_BY_ISLEAF has_child
FROM 
  t_folders f
CONNECT BY 
  PRIOR f.id = f.parent_id
START WITH
  f.parent_id IS NULL;

SELECT
  p.path, 
  h.weight
FROM
  (
    SELECT
      h.id, 
      h.type, 
      h.weight
    FROM
      (
        SELECT
          f.id, 
          LEVEL nested_level,
          SUM(f.weight) OVER (PARTITION BY CONNECT_BY_ROOT(f.id)) weight, 
          f.type
        FROM
          (
            (
              SELECT
                f.id, 
                f.parent_id, 
                f.name, 
                0 weight, -- A folder has no weight
                'FOLDER' type -- Used to distinguish folders and file
              FROM
                t_folders f
            ) UNION ALL (
              SELECT
                -1 id, -- We use a fake ID to be consistent
                f.folder_id parent_id,
                f.name, 
                f.weight, 
                'FILE' type
              FROM
                t_files f
            )
          ) f
        CONNECT BY 
          PRIOR f.id = f.parent_id
      ) h
    WHERE
          h.nested_level = 1
      AND h.type = 'FOLDER'
  ) h
JOIN 
  (
    SELECT 
      f.id,
      SYS_CONNECT_BY_PATH(f.name, '/') path
    FROM 
      t_folders f
    CONNECT BY 
      PRIOR f.id = f.parent_id
    START WITH
      f.parent_id IS NULL
  ) p
ON
      p.id = h.id;


DROP TABLE 
  t_files;

DROP TABLE 
  t_folders;