MySQL 8.0 - Difficulty with Recursive CTE and performance optimization on Hierarchical Data Retrieval
I've been working on this all day and I can't seem to get I'm working with a important performance scenario when using a Recursive Common Table Expression (CTE) to retrieve hierarchical data in MySQL 8.0. My data structure consists of a `categories` table with a parent-child relationship, defined by `id` and `parent_id`. The CTE works correctly for small datasets, but as the dataset grows (we're talking about thousands of categories), the performance degrades noticeably, taking several seconds to return results. Here’s the CTE query I’m using: ```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; ``` On execution, I receive no errors, but the execution time is problematic compared to simpler queries. I've tried adding indexes on both `id` and `parent_id`, but that didn’t yield the expected performance improvement. I also experimented with limiting the depth of recursion by adding a depth counter, but it didn't seem to help much either. Additionally, I noticed that the query planner is not utilizing the indexes effectively, which might be a contributing factor. In the `EXPLAIN` output, it often shows "Using temporary" and "Using filesort" which raises concerns about the efficiency of my query. Could anyone suggest optimizations or best practices for handling this type of recursive data retrieval in MySQL, especially for larger datasets? Is there a better approach or alternative methods I should consider? Any help would be greatly appreciated! I've been using Sql for about a year now. Any ideas what could be causing this? This issue appeared after updating to Sql LTS. I'm open to any suggestions.