Strange results using FULL OUTER JOIN in PostgreSQL when combining NULLs with GROUP BY
I'm working through a tutorial and I tried several approaches but none seem to work... I tried several approaches but none seem to work... I'm working with unexpected behavior when using a `FULL OUTER JOIN` in PostgreSQL 14. I'm trying to combine two tables, `orders` and `customers`, and I want to aggregate the results based on the customer ID. However, when there are NULL values in the customer IDs, the output seems inconsistent. Here's a simplified version of my query: ```sql SELECT c.id AS customer_id, COUNT(o.id) AS order_count FROM customers c FULL OUTER JOIN orders o ON c.id = o.customer_id GROUP BY c.id ORDER BY customer_id; ``` The scenario arises when there are customers without any orders. Instead of getting a `0` for the `order_count`, I see `NULL`. I've tried using `COALESCE` to replace NULLs with zeros like this: ```sql SELECT c.id AS customer_id, COALESCE(COUNT(o.id), 0) AS order_count FROM customers c FULL OUTER JOIN orders o ON c.id = o.customer_id GROUP BY c.id ORDER BY customer_id; ``` This doesn't change the results; I still get `NULL` in the `order_count` for customers without orders. I’ve also tried using `LEFT JOIN` instead of `FULL OUTER JOIN`, but I need the full dataset from both tables. Is there a way to ensure that customers without orders show a count of `0` instead of `NULL` while still using `FULL OUTER JOIN`? Any guidance on why this is happening would be greatly appreciated. Thanks in advance! I'm coming from a different tech stack and learning Sql. The project is a mobile app built with Sql. I'd be grateful for any help.