PostgreSQL: Unexpected NULL results when using COALESCE in SELECT with LEFT JOIN
I'm sure I'm missing something obvious here, but I'm sure I'm missing something obvious here, but I've looked through the documentation and I'm still confused about I'm working with an scenario where my query returns NULLs for values that I expect to be filled in by the `COALESCE` function... I have two tables, `users` and `orders`, where I want to list all users along with their latest order total. However, for some users who do not have any orders, I want to display 0 instead of NULL. Here's the query I've constructed: ```sql SELECT u.id AS user_id, COALESCE(SUM(o.total), 0) AS total_order_value FROM users u LEFT JOIN orders o ON u.id = o.user_id GROUP BY u.id; ``` Surprisingly, I get NULL in the `total_order_value` column for users without orders instead of 0. I suspect it has something to do with how the `SUM` function interacts with the `LEFT JOIN`. I've also tried various combinations of `COALESCE` and `SUM` with no luck. When I run it, I see results like this: | user_id | total_order_value | |---------|-------------------| | 1 | NULL | | 2 | 150 | | 3 | NULL | I want the result to show 0 for user 1 and 3. Iām using PostgreSQL 14.1, and according to the documentation, `COALESCE` should work as expected here. Are there any subtleties I might be missing, or perhaps a mistake in my SQL syntax? Any help would be greatly appreciated! For context: I'm using Sql on Ubuntu. I'm working on a service that needs to handle this. Has anyone else encountered this?