Find all related records - sql

Question

I have an Order table that has a LinkedOrderID field.
I would like to build a query that finds all linked orders and returns them in the result set.
select OrderID,LinkOrderID from [Order] where LinkOrderID is not null
OrderID LinkOrderID
787016 787037
787037 787786
787786 871702
I would like a stored proc that returns the following:
OrderID InheritanceOrder
787016 1
787037 2
787786 3
871702 4
I would also like to make sure I don't have an infinite loop

Answer 1

DECLARE #Order TABLE (OrderID INT NOT NULL, LinkOrderID INT NOT NULL)
INSERT
INTO #Order
VALUES (787016, 787037)
INSERT
INTO #Order
VALUES (787037, 787786)
INSERT
INTO #Order
VALUES (787786, 871702)
/*
INSERT
INTO #Order
VALUES (871702, 787016)
*/
;WITH q (OrderId, LinkOrderId, InheritanceOrder, FirstItem) AS
(
SELECT OrderID, LinkOrderId, 1, OrderID
FROM #Order
WHERE OrderID = 787786
UNION ALL
SELECT o.OrderId, o.LinkOrderId, q.InheritanceOrder + 1, q.FirstItem
FROM q
JOIN #Order o
ON o.OrderID = q.LinkOrderId
WHERE o.OrderID <> q.FirstItem
UNION ALL
SELECT LinkOrderId, NULL, q.InheritanceOrder + 1, q.FirstItem
FROM q
WHERE q.LinkOrderID NOT IN
(
SELECT OrderID
FROM #Order
)
)
SELECT OrderID, InheritanceOrder
FROM q
ORDER BY
InheritanceOrder
This assumes that both OrderID and LinkOrderID are unique (i. e. it's a linked list, not a tree).
Works with the last insert uncommented too (which makes a loop)

Answer 2

To check for an infinite loop, there are two checks:
First, make sure that you start with an _id that ever appears in the LinkOrderID
select o1.OrderID from Order o1
left outer join Order o2 on o1.OrderId = o2.LinkOrderID
where o2.LinkOrderID is null;
This will give you a list that are the starts of your linked lists.
Then, make sure none of your _ids ever show up more than once.
select * from {
select LinkOrderId, count(*) as cnt from Order
} where cnt > 1;
If these two conditions are true (you are starting from an order that never appears in the Linked list and you have no OrderIds that are linked multiple times) then you can't have a loop.

Answer 3

Sweet: i found the solution thanks to Quassnoi's awesome code. I tweaked it to first walk up to the oldest parent, and then walk down through all children. Thanks again!
-- =============================================
-- Description: Gets all LinkedOrders for OrderID.
-- It will first walk up and find oldest linked parent, and then next walk down recursively and find all children.
-- =============================================
alter PROCEDURE Order_Order_GetAllLinkedOrders
(
#StartOrderID int
)
AS
--Step#1: find oldest parent
DECLARE #oldestParent int
;WITH vwFirstParent (OrderId) AS
(
SELECT OrderID
FROM [Order]
WHERE OrderID = #StartOrderID
UNION ALL
SELECT o.OrderId
FROM vwFirstParent
JOIN [Order] o
ON o.LinkOrderID = vwFirstParent.OrderId
)
select #oldestParent = OrderID from vwFirstParent
--Step#2: find all children, prevent recursion
;WITH q (OrderId, LinkOrderId, InheritanceOrder, FirstItem) AS
(
SELECT OrderID, LinkOrderId, 1, OrderID
FROM [Order]
WHERE OrderID = #oldestParent
UNION ALL
SELECT o.OrderId, o.LinkOrderId, q.InheritanceOrder + 1, q.FirstItem
FROM q
JOIN [Order] o
ON o.OrderID = q.LinkOrderId
WHERE o.OrderID <> q.FirstItem
UNION ALL
SELECT LinkOrderId, NULL, q.InheritanceOrder + 1, q.FirstItem
FROM q
WHERE q.LinkOrderID NOT IN
(
SELECT OrderID
FROM [Order]
)
)
SELECT OrderID,LinkOrderId, InheritanceOrder
FROM q