MySQL 8.0 - advanced patterns with CTEs and Recursive Queries for Hierarchical Data
I've looked through the documentation and I'm still confused about I'm working with an scenario with recursive Common Table Expressions (CTEs) when trying to retrieve hierarchical data from a MySQL 8.0 database. I have a table called `categories` structured as follows: ```sql CREATE TABLE categories ( id INT PRIMARY KEY, name VARCHAR(100), parent_id INT, FOREIGN KEY (parent_id) REFERENCES categories(id) ); ``` The table is populated with some categories and their parent-child relationships. I'm trying to construct a query to retrieve all categories under a specific parent using a recursive CTE. However, I keep getting an empty result set when I expect to see multiple rows. Here's the query I'm using: ```sql WITH RECURSIVE category_tree AS ( SELECT id, name, parent_id FROM categories WHERE id = 1 -- Starting with the root category UNION ALL SELECT c.id, c.name, c.parent_id FROM categories c INNER JOIN category_tree ct ON c.parent_id = ct.id ) SELECT * FROM category_tree; ``` I've double-checked that the category with `id = 1` exists and has children. When I run the first part of the CTE without the recursive part, I do get the expected result. I'm trying to figure out whether I'm missing something in my JOIN condition or if there's a setting in MySQL that I need to adjust. Additionally, I've noticed that when I run this query, it takes significantly longer to execute than I anticipated. I tried checking the execution plan using `EXPLAIN`, but it didn't seem to provide any insights on why the results are not coming through. Any suggestions on what I might be doing wrong or how I can optimize this query? My team is using Sql for this CLI tool. Is this even possible?