Hierarchical query rollup Rollup - tsql

Question

I have the following table:
parent_id child_id child_class
1 2 1
1 3 1
1 4 2
2 5 2
2 6 2
Parent_id represents a folder id. Child id represents either a child folder (where child_class=1) or child file (where child_class=2).
I'd like to get a rollup counter (bottom up) of all files only (child_class=2) the following way. for example if C is a leaf folder (no child folders) with 5 files, and B is a parent folder of C that has 4 files in it, the counter on C should say 5 and the counter on B should say 9 (=5 from C plus 4 files in B) and so forth recursively going bottom up taking into consideration sibling folders etc.
In the example above I expect the results below (notice 3 is a child folder with no files in it):
parent_id FilesCounter
3 0
2 2
1 3
I prefer an SQL query for performance but function is also possible.
I tried mixing hirarchical query with rollup (sql 2008 r2) with no success so far.
Please advise.

Answer 1

This CTE should do the trick... Here is the SQLFiddle.
SELECT parent_id, child_id, child_class,
(SELECT COUNT(*) FROM tbl a WHERE a.parent_id = e.parent_id AND child_class <> 1) AS child_count
INTO tbl2
FROM tbl e
;WITH CTE (parent_id, child_id, child_class, child_count)
AS
(
-- Start with leaf nodes
SELECT parent_id, child_id, child_class, child_count
FROM tbl2
WHERE child_id NOT IN (SELECT parent_id from tbl)
UNION ALL
-- Recursively go up the chain
SELECT e.parent_id, e.child_id, e.child_class, e.child_count + d.child_count
FROM tbl2 e
INNER JOIN CTE AS d
ON e.child_id = d.parent_id
)
-- Statement that executes the CTE
SELECT FOLDERS.parent_id, max(ISNULL(child_count,0)) FilesCounter
FROM (SELECT parent_id FROM tbl2 WHERE parent_id NOT IN (select child_id from tbl2)
UNION
SELECT child_id FROM tbl2 WHERE child_class = 1) FOLDERS
LEFT JOIN CTE ON FOLDERS.parent_id = CTE.parent_id
GROUP BY FOLDERS.parent_id

Answer 2

Zak's answer was close, but the root folder did not rollup well. The following does the work:
with par_child as (
select 1 as parent_id, 2 as child_id, 1 as child_class
union all select 1, 3, 1
union all select 1, 4, 2
union all select 2, 5, 1
union all select 2, 6, 2
union all select 2, 10, 2
union all select 3, 11, 2
union all select 3, 7 , 2
union all select 5, 8 , 2
union all select 5, 9 , 2
union all select 5, 12, 1
union all select 5, 13, 1
)
, child_cnt as
(
select parent_id as root_parent_id, parent_id, child_id, child_class, 1 as lvl from par_child union all
select cc.root_parent_id, pc.parent_id, pc.child_id, pc.child_class, cc.lvl + 1 as lvl from
par_child pc join child_cnt cc on (pc.parent_id=cc.child_id)
),
distinct_folders as (
select distinct child_id as folder_id from par_child where child_class=1
)
select root_parent_id, count(child_id) as cnt from child_cnt where child_class=2 group by root_parent_id
union all
select folder_id, 0 from distinct_folders df where not exists (select 1 from par_child pc where df.folder_id=pc.parent_id)