TSQL GROUP BY in recursive CTE - sql-server

Question

Is there a workaround to use GROUP BY inside a looping CTE or there is a workaround?
I need to group resultset of a CTE table and use it in another loop with the same CTE, but i get following error:
GROUP BY, HAVING, or aggregate functions are not allowed in the
recursive part of a recursive common table expression 'cte'.
Here's the query:
WITH cte
AS
(
SELECT
id,
dailyconsumption,
stock/dailyconsumption as cutoff
FROM items
WHERE father IS NULL
UNION ALL
SELECT
i.id,
SUM(father.dailyconsumption*i.num),
MAX(stock)/SUM(father.dailyconsumption*i.num)
FROM cte father
JOIN items i ON father.id=i.father
group by i.id
)
SELECT id, MIN(cutoff)
FROM cte
GROUP BY id
SQL-Fiddle (with sample data)
EDIT... this is the logical problem
I have a set of end-user items (father=NULL) and other sub-items made by a number of other items (field father and field num populated).
I got the dailyconsumption just for the end-user items (I start my cte with "WHERE father IS NULL"), and sub-items's dailyconsumption are calculate by SUM(father.dailyconsumption *item.num).
WITH cte AS(
SELECT
id,
dailyconsumption,
stock/dailyconsumption as cutoff
FROM items
WHERE father IS NULL
UNION ALL
SELECT
i.id,
father.dailyconsumption*i.num
0
FROM cte father
JOIN items i ON father.id=i.father
)
SELECT id, SUM(dailyconsumption)
FROM cte
GROUP BY id
http://sqlfiddle.com/#!3/f4f2a/95
With this valid query I'm going to have all dailyconsumption populated for all items (end-user and sub-items). Please mind that father-son relationship can be more than 1 level deep.
Now i need to calculate the cutoff (for how many days my stock is enought).
For end-use it is very easy and already calculated in first CTE: stock/dailyconsumption.
For sub-items it is a little more complicated:
subitem.stock/subitem.dailyconsumption + MIN(father.cutoff)
where MIN(father.cutoff) is the minimun cutoff from all fathers of this subitem.
This is because i need another group by.
May I need another CTE to loop in the same father-son relationship?
Thank you for your attention and sorry for my English.

Answer 1

;WITH cte AS
(
SELECT id, father,
dailyconsumption,
(stock / dailyconsumption) AS cutoff,
0 AS [Level]
FROM items
WHERE father IS NULL
UNION ALL
SELECT i.id, i.father,
c.dailyconsumption * i.num,
i.stock / (c.dailyconsumption * i.num),
[Level] + 1
FROM cte c JOIN items i ON c.id = i.father
)
SELECT c.id, c.dailyconsumption, c.cutoff AS subItemsCutoff,
MIN(ct.cutoff) OVER(PARTITION BY ct.[Level]) AS fatherCutoff,
(c.cutoff + ISNULL(MIN(ct.cutoff) OVER(PARTITION BY ct.[Level]), 0)) AS Cutoff
FROM cte c LEFT JOIN cte ct ON c.father = ct.id
Demo on SQLFiddle

Answer 2

I recommend using a variable table instead. Declare the table and then insert those records into it. You would need to figure out a way to loop through it on the second insert into command. I got this to get you started:
DECLARE #staging TABLE
(
id INT
,dailyconsumption FLOAT
,cutoff FLOAT
)
INSERT INTO #staging
SELECT
id,
dailyconsumption,
stock/dailyconsumption as cutoff
FROM
items
WHERE
father IS NULL
INSERT INTO #staging
SELECT
i.id,
SUM(father.dailyconsumption*i.num),
MAX(stock)/SUM(father.dailyconsumption*i.num)
FROM
#staging father
JOIN items i
ON father.id=i.father
group by
i.id
SELECT
id
,MIN(cutoff)
FROM
#staging
GROUP BY
id