Tsql looping father-son relationship between tables - sql

Question

I have a table like this:
table item
(
id int,
quantity float,
father int, -- refer to item itself in case of subitem
)
I need to sum al quantity plus sons quantity like this way:
select i.id, max(i.quantity)+sum(ft.quantity) as quantity
from item i
left join item ft on ft.id=i.id
group by i.id
My trouble is because relationship between father-son is recursive so I would like to sum also his grandfather quantity and so on... and i don't know the maximum deepness, than I can not join many times.
What can i do?
Thank you.

Answer 1

You have to use a recursive CTE. Somthing like this:
;WITH FathersSonsTree
AS
(
SELECT Id, quantity, 0 AS Level
FROM Items WHERE fatherid IS NULL
UNION ALL
SELECT c.id, c.quantity, p.level+1
FROM FathersSonsTree p
INNER JOIN items c ON c.fatherid = p.id
), ItemsWithMaxQuantities
AS
(
SELECT *,
ROW_NUMBER() OVER(PARTITION BY level
ORDER BY quantity DESC) rownum
FROM FathersSonsTree
)
SELECT
ID,
(SELECT MAX(Quantity)
FROM FathersSonsTree t3
WHERE t3.level = t1.level
) +
ISNULL((SELECT SUM(t2.Quantity)
FROM FathersSonsTree t2
WHERE t1.level - t2.level = 1), 0)
FROM FathersSonsTree t1
ORDER BY ID;
SQL Fiddle Demo
This will give you something like:
| ID | QUANTITY |
-----------------
| 1 | 10 |
| 2 | 20 |
| 3 | 20 |
| 4 | 20 |
| 5 | 32 |
| 6 | 32 |
| 7 | 32 |
| 8 | 32 |

Answer 2

You might try building a recursive CTE (common table expression) as described in this article on SQLAuthority:
http://blog.sqlauthority.com/2012/04/24/sql-server-introduction-to-hierarchical-query-using-a-recursive-cte-a-primer/
The author, Pinal Dave, discusses using a recursive CTE on an employees table that has a self referencing foreign key for ManagerID to return a list of employees with a count of how many levels are between them and the top of the hierarchy where the employee has no manager (ManagerID = NULL). That's not exactly what you're wanting but it might get you started.
I did a little experimentation and ended up with something very similar to Mahmoud Gamal's solution but with a slight difference to include the not just the parent, grandparents, great-grandparents, etc. quantity but also the child quantity.
Here's the test table I used:
CREATE TABLE Items(ID int IDENTITY
CONSTRAINT PK_Items PRIMARY KEY,
Quantity int NOT NULL,
ParentID int NULL
CONSTRAINT FK_Item_Parents REFERENCES Items(ID));
And the data:
ID Quantity ParentID
------------------------------------------------------------
1 10 {NULL}
2 10 1
3 10 2
4 10 3
5 10 2
Here's my recursive query:
WITH cteRecursiveItems
AS (SELECT Id,
quantity,
0
AS Level
FROM Items
WHERE ParentID IS NULL
UNION ALL
SELECT i.id,
i.quantity,
cri.level + 1
FROM
cteRecursiveItems cri
INNER JOIN items i ON i.ParentID = cri.id)
SELECT ID,
Quantity + (
SELECT MAX(Quantity)
FROM cteRecursiveItems cri3
WHERE cri3.level = cri1.level) + (
SELECT SUM(cri2.Quantity)
FROM cteRecursiveItems cri2
WHERE cri1.level - cri2.level = 1) as Total
FROM cteRecursiveItems cri1
ORDER BY ID;
And here's the results I get from running it against the test table:
ID Total
----------------------------------------
1 {NULL}
2 30
3 30
4 40
5 30
It still needs a little tweaking because the first and 2nd row are off by 10. Row 1 should have a total of 10 and row 2 should have a total of 20. I'm making a note to try and fix that when I get home. Can't spend too much of my employer's time on this right now. :) The other rows have the value I was expecting.