MySQL 5.7: Inconsistent results with GROUP BY and NULL values in LEFT JOINs
I'm deploying to production and Hey everyone, I'm running into an issue that's driving me crazy. I'm working with an scenario with MySQL 5.7 where my query returns inconsistent results when using `GROUP BY` with `NULL` values in a `LEFT JOIN`. I have two tables: `orders` and `customers`, where an order can exist without a corresponding customer. Here's my query: ```sql SELECT c.id, COUNT(o.id) AS order_count FROM customers c LEFT JOIN orders o ON c.id = o.customer_id GROUP BY c.id; ``` The expectation is that customers without orders should show an order count of zero. However, the results seem to show `NULL` for some customers instead, which I didn't anticipate. After reviewing my query, I tried modifying it by replacing `GROUP BY c.id` with `GROUP BY COALESCE(c.id, -1)`, but that only resulted in incorrect grouping. I also experimented with using `IFNULL(COUNT(o.id), 0)` instead of `COUNT(o.id)`, but it still shows `NULL` for customers with no orders. I checked my data, and I can confirm that there are customers without any orders, and they should display as zero in my results. Is there something I'm missing in the use of `GROUP BY` with `LEFT JOIN` in this context, or is there a specific behavior in MySQL 5.7 that I should be aware of? Any insights would be greatly appreciated! Any help would be greatly appreciated! This is happening in both development and production on CentOS. Has anyone else encountered this?