SQL Server: Problems with Recursive CTE for Hierarchical Data Retrieval
Hey everyone, I'm running into an issue that's driving me crazy. I need some guidance on I'm working with SQL Server 2019 and trying to retrieve hierarchical data using a recursive Common Table Expression (CTE) to get the full tree structure of categories and their subcategories. However, I'm running into an scenario where the CTE seems to be returning duplicate rows for some parent categories. The base query seems to work fine, but when I add the recursive part, I notice that some categories appear multiple times in the final result set. Here’s the CTE I'm using: ```sql WITH CategoryHierarchy AS ( SELECT CategoryID, ParentCategoryID, CategoryName FROM Categories WHERE ParentCategoryID IS NULL -- Start with top-level categories UNION ALL SELECT c.CategoryID, c.ParentCategoryID, c.CategoryName FROM Categories c INNER JOIN CategoryHierarchy ch ON c.ParentCategoryID = ch.CategoryID ) SELECT * FROM CategoryHierarchy; ``` I've checked that there are no duplicates in the initial `Categories` table. To debug, I added a `DISTINCT` clause, but it doesn’t seem to resolve the scenario. The duplicates appear to be related to categories that have multiple subcategories linked to the same parent, and I want to ensure I’m not missing anything in my logic. Is there a better approach to handle this or a way to eliminate duplicates in the result without affecting the structure? Any insights would be appreciated! Additionally, I’ve confirmed that the relationships in the table are set up correctly and that there are no circular references. I'm worried that this might be a performance scenario as well since the dataset will grow significantly in production. How can I optimize this query further if necessary? For context: I'm using Sql on Linux. What's the correct way to implement this? The stack includes Sql and several other technologies. What's the best practice here?