👀 Views: 73 💬 Answers: 1 📅 Created: 2025-06-07

postgresql sql array-agg SQL

I'm working on a personal project and I'm a bit lost with I've looked through the documentation and I'm still confused about I'm working with an scenario with my PostgreSQL query that utilizes the `array_agg()` function in the `SELECT` clause. The goal is to retrieve a list of product names associated with each category. However, I'm getting a 'subquery returned more than one row' behavior when I try to execute the query. Here's the code I'm currently using: ```sql SELECT c.category_id, c.category_name, (SELECT array_agg(p.product_name) FROM products p WHERE p.category_id = c.category_id) FROM categories c; ``` I've tried to troubleshoot this by ensuring that `category_id` in the `products` table correctly matches the `category_id` in the `categories` table. The `products` table has the following structure: ```sql CREATE TABLE products ( product_id SERIAL PRIMARY KEY, product_name VARCHAR(255) NOT NULL, category_id INT REFERENCES categories(category_id) ); ``` When I run the subquery independently, it works fine and returns multiple product names in an array for a specific category. But when I attempt to run the complete query, I get the behavior mentioned above. I suspect the scenario might stem from the way I’m using the subquery. Is there a better way to achieve this? I've also tried using a `JOIN` instead of a subquery, but then I end up with duplicate records in the output. Here's that attempt: ```sql SELECT c.category_id, c.category_name, array_agg(p.product_name) AS product_names FROM categories c LEFT JOIN products p ON p.category_id = c.category_id GROUP BY c.category_id, c.category_name; ``` This version works without errors, but it doesn't satisfy my requirement of returning specific columns from both tables when there are no products in a category. Any help or guidance on how to resolve this would be greatly appreciated! Has anyone dealt with something similar? I'm working in a Linux environment.