Recursive Query CTE Father - Son - Grandson error - sql

Question

I have a table that has an ID and IDFATHER of some projects, these projects can receive N sons, so, the structure is like
ID
IDFATHER
REV
1
1
0
2
1
1
5
2
2
I need to, iniciating in ID 5 go to ID 1, so I did a CTE Query:
WITH lb (ID, IDFATHER) AS (
SELECT ID, IDFATHER
FROM PROJECTS
WHERE ID = 5
UNION ALL
SELECT I.ID, I.IDFATHER
FROM PROJECTS I
JOIN lb LBI ON I.ID = LBI.IDFATHER
--WHERE I.ID = LBI.IDFATHER -- Recursive Subquery
)
SELECT *
FROM lb
WHERE LB.ID = LB.IDFATHER
When this code runs it gives me:
The statement terminated. The maximum recursion 100 has been exhausted
before statement completion.
So basically I handle it by just adding:
SELECT TOP 1 * FROM LB WHERE LB.ID = LB.IDFATHER
But I really want to know were is my error. Can anyone give me a hand on these?

Answer 1

The first row points to itself so the recursion never stops. You need to add this condition inside the recursive cte:
WHERE LBI.ID <> LBI.IDFATHER
I would rather set IDFather of the first row to NULL.

Answer 2

The recursion didn't stop because your top row refers to itself endlessly.
If the top row has a null parent, that would have stopped the recursion.
Another approach is to use that case id = parentid as the termination logic.
The fiddle
WITH LB (ID, IDFATHER, idstart) AS (
SELECT ID, IDFATHER, id
FROM PROJECTS WHERE ID = 5
UNION ALL
SELECT I.ID, I.IDFATHER, lbi.idstart
FROM PROJECTS I
JOIN LB LBI
ON I.ID = lbi.IDFATHER
AND lbi.id <> lbi.idfather
)
SELECT id AS idtop, idstart
FROM LB
WHERE LB.ID = LB.IDFATHER
;
The result: