👀 Views: 907 💬 Answers: 1 📅 Created: 2025-07-05

mysql performance ctes recursive sql

I've been banging my head against this for hours. I'm currently working on a project that requires me to generate a hierarchy of categories for a product listing. To achieve this, I've implemented a recursive Common Table Expression (CTE) in MySQL 8.0 to fetch nested categories. However, I've noticed important performance optimization when the category tree has a large depth (e.g., over 10 levels) and contains thousands of categories. The query takes an unusually long time to execute, and I'm not sure if I’m doing something wrong or if there's a better way to handle this. Here's the CTE I've written: ```sql WITH RECURSIVE category_tree AS ( SELECT id, name, parent_id FROM categories WHERE parent_id IS NULL UNION ALL SELECT c.id, c.name, c.parent_id FROM categories c INNER JOIN category_tree ct ON ct.id = c.parent_id ) SELECT * FROM category_tree; ``` When I run this query, it sometimes takes over 30 seconds to complete, especially when the `categories` table is populated with a lot of data. I tried to optimize it by ensuring that indexes are set on `id` and `parent_id`, but the performance hasn't improved significantly. Additionally, I encountered the following warning in the logs: ``` Warning (Code: 1235): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' ``` I'm not using any subqueries in the CTE itself, so I’m baffled as to why this warning appears. I've also tried limiting the depth of recursion using a `MAXRECURSION` clause, but it didn't help with performance. Is there a specific reason why recursive CTEs perform poorly with deep hierarchies in MySQL? Are there any alternative strategies or optimizations I should consider to improve the execution time of this query? Any insights would be greatly appreciated! For reference, this is a production mobile app. Any examples would be super helpful.