MySQL 8.0: Unexpected NULL values when using LEFT JOIN with multiple conditions
I'm stuck on something that should probably be simple. I'm experiencing unexpected NULL values in my result set when executing a query with a LEFT JOIN that includes multiple conditions. I'm working with MySQL 8.0 and the goal is to retrieve all records from the main table even if there are no matching records in the joined table. Here's the query I'm using: ```sql SELECT a.id, a.name, b.status FROM users AS a LEFT JOIN orders AS b ON a.id = b.user_id AND b.status = 'active' WHERE a.created_at > '2023-01-01'; ``` This query is intended to return all users created after January 1, 2023, and their corresponding active order statuses. However, I noticed that when a user has no active orders, the `status` field returns NULL, which is expected. The question arises when a user does have orders, but those orders do not match the condition of being 'active'; in this case, the row is still included in the result set, but the status is also NULL. To troubleshoot, I added the following subquery to see the count of orders for each user: ```sql SELECT a.id, a.name, (SELECT COUNT(*) FROM orders AS b WHERE b.user_id = a.id) AS order_count FROM users AS a WHERE a.created_at > '2023-01-01'; ``` This shows that users with orders are being counted correctly, but the status still returns NULL in the original LEFT JOIN query. I've also attempted modifying the join condition to check for a specific order ID, which didn't yield any change. I checked the database for the existence of orders with the status 'active' and confirmed that there are records that should match. Can someone guide to understand why the status is returning NULL in this case? Is there a better way to structure the query to ensure that users with non-active orders still show a valid status? Any insights into how the join condition might affect the results would be greatly appreciated. Thanks! My development environment is macOS. Thanks in advance!