SQL Server 2019: Handling Recursive CTEs for Hierarchical Data with Unexpected Stack Overflow
I'm relatively new to this, so bear with me... I'm trying to use a Common Table Expression (CTE) to retrieve a hierarchical structure from a SQL Server 2019 database. The hierarchy is based on a parent-child relationship stored in a single table. However, when I run my query, I'm working with a stack overflow behavior, and I'm not sure why it's happening. Here’s the query I’m using: ```sql WITH RecursiveCTE AS ( SELECT Id, Name, ParentId FROM Categories WHERE ParentId IS NULL UNION ALL SELECT c.Id, c.Name, c.ParentId FROM Categories c INNER JOIN RecursiveCTE r ON c.ParentId = r.Id ) SELECT * FROM RecursiveCTE; ``` The `Categories` table looks like this: | Id | Name | ParentId | |----|---------|----------| | 1 | Books | NULL | | 2 | Fiction | 1 | | 3 | Sci-Fi | 2 | | 4 | Non-Fiction | 1 | | 5 | History | 4 | I’ve verified that the data is correct, and initially, it seems to work for smaller datasets. However, when I increase the number of rows or include more nested levels, I start getting this behavior: ``` SQL Server has encountered a stack overflow exception. ``` I've read that this might happen due to infinite recursion, but I don’t see any obvious circular references in my data. I’ve also tried adding a `OPTION (MAXRECURSION 100)` clause to limit the recursion depth, but this doesn’t seem to resolve the scenario. Additionally, I’ve checked the execution plan, and it looks like the recursion is going deeper than expected. Is there a best practice or configuration that I might be missing? Any suggestions on how to handle this more efficiently would be greatly appreciated! I'm working on a API that needs to handle this. Has anyone else encountered this?