### Communities

tag:snake search within a tag
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
created:<1w created < 1 week ago
post_type:xxxx type of post
Q&A

Welcome to Software Development on Codidact!

Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.

Parent

# How to break infinite loop in CTE

+5
−0

I have a parent-child relation in my table, with possibly circular cases. Is it possible to break the infinite recursion in CTE checking values of all previous rows? I would need something like this:

with my_cte(childId, parentId, col1)
AS (
SELECT r.childId, r.parentId, r.col1
FROM My_Table r WHERE r.childId = 'x' AND (r.col1 = 1 or r.col1 = 2)
UNION ALL
SELECT rel.childId, rel.parentId, rel.col1
FROM My_Table rel INNER JOIN my_cte sd ON rel.childId = sd.parentId where (rel.col1 = 1 OR rel.col1 = 2) AND ...
-- check that rel.childId, rel.parentId not in previous rows
)
SELECT DISTINCT * from shared_documents


How can I achieve this? Or how to approach this?

Example table with records would be:

childId parentId col1
1 3 1
1 4 1
3 5 1
5 1 1 -- circular case
6 2 1
5 7 1

If I ask for hierarchy related to 1, I should get

childId parentId col1
1 3 1
1 4 1
3 5 1
5 1 1 -- circular case
5 7 1
• 1 has two parents: 3 and 4.
• 3 has 1 parent: 5
• 5 has 2 parents: 1 and 7. But 1 brings the infinite loop, so the query should ignore this. And continue to the next row.
Why does this post require moderator attention?
Why should this post be closed?

Post
+2
−0

For small tables you can bound the recursion depth:

WITH my_cte(childId, parentId, depth, max_depth)
AS (
SELECT r.childId, r.parentId, 1, (SELECT COUNT(*) FROM My_Table)
FROM My_Table r
WHERE r.childId = 1

UNION ALL

SELECT rel.childId, rel.parentId, sd.depth + 1, sd.max_depth
FROM My_Table rel INNER JOIN my_cte sd ON rel.childId = sd.parentId
WHERE sd.depth < sd.max_depth
)
SELECT DISTINCT childId, parentId
FROM my_cte


This approach is limited by the bound that MAXRECURSION <= 32767.

Why does this post require moderator attention?