👀 Views: 42 💬 Answers: 1 📅 Created: 2025-06-11

mysql sql join subquery SQL

I'm confused about I've looked through the documentation and I'm still confused about I'm experiencing an scenario with MySQL 8.0 where using a subquery in a JOIN results in an unexpected empty result set... I have two tables, `orders` and `customers`. My intention is to retrieve all orders along with the customer's name, but when I include a subquery to filter customers based on their status, the results come back empty. Here's the query I'm using: ```sql SELECT o.order_id, o.order_date, c.name FROM orders o JOIN ( SELECT id, name FROM customers WHERE status = 'active' ) c ON o.customer_id = c.id; ``` In this case, I expect to see all active customers with their corresponding orders. However, when I run the query, I get an empty result set. I checked the `customers` table, and there are definitely active customers, so I don't understand why nothing is being returned. I tried simplifying the query by removing the subquery and just using the `customers` table directly, and that worked fine: ```sql SELECT o.order_id, o.order_date, c.name FROM orders o JOIN customers c ON o.customer_id = c.id WHERE c.status = 'active'; ``` This returns results as expected, which makes me think there's something wrong with how the subquery is being handled. I also ensured that the `customer_id` in `orders` aligns correctly with `id` in `customers`, and both are indexed, so performance shouldn't be an scenario. Has anyone encountered this specific behavior with subqueries in JOINs? Is there a best practice or a common pitfall I might be missing here? Has anyone else encountered this? I'm on Linux using the latest version of Sql.