Trouble with Recursive Common Table Expressions in PostgreSQL 14 for Hierarchical Data
I'm working on a personal project and I'm trying to debug I'm working on a project and hit a roadblock. I've been banging my head against this for hours... I'm working with a PostgreSQL 14 database where I need to retrieve hierarchical data from a self-referential table representing categories and subcategories. I've created a recursive Common Table Expression (CTE) to get all subcategories under a specific parent category, but I'm working with an scenario where it doesn't return the expected results for deeper levels of hierarchy. Here's the structure of my `categories` table: ```sql CREATE TABLE categories ( id SERIAL PRIMARY KEY, name VARCHAR(255), parent_id INT REFERENCES categories(id) ); ``` And this is the recursive CTE I wrote: ```sql WITH RECURSIVE category_hierarchy AS ( SELECT id, name, parent_id FROM categories WHERE id = 1 -- starting from the root category with id 1 UNION ALL SELECT c.id, c.name, c.parent_id FROM categories c INNER JOIN category_hierarchy ch ON c.parent_id = ch.id ) SELECT * FROM category_hierarchy; ``` When I run this query, I only get the immediate subcategories and not the deeper nested ones. I expected to see all levels of categories under the specified parent. I also tried adjusting the CTE by including the `ORDER BY` clause and modifying the base case condition, but it didn't seem to affect the output. Here’s the output I'm getting: ``` id | name | parent_id ----+-----------------+------------ 2 | Subcategory A | 1 3 | Subcategory B | 1 (2 rows) ``` However, there are additional subcategories under `Subcategory A` that should also be displayed. I checked the data and confirmed that the hierarchy is correctly set up. Can anyone guide to understand why this is happening or if there's a need to tweak the query further? Any insights on best practices for using recursive CTEs in this context would also be appreciated. My development environment is macOS. Am I missing something obvious? I'm developing on Windows 10 with Sql. The stack includes Sql and several other technologies. Any suggestions would be helpful.