PostgreSQL: scenarios on Aggregate Function with DISTINCT and Join Condition
I'm stuck trying to I'm converting an old project and I'm sure I'm missing something obvious here, but Quick question that's been bugging me - I'm working on a project and hit a roadblock... I'm working with a strange scenario when trying to aggregate data from two joined tables in PostgreSQL 14. I want to count distinct user actions from a `user_actions` table while filtering based on user IDs from a `users` table. The query runs without errors, but the results seem off. Here's what I have: ```sql SELECT u.id, COUNT(DISTINCT a.action) AS distinct_actions FROM users u JOIN user_actions a ON u.id = a.user_id WHERE u.active = TRUE GROUP BY u.id; ``` This query should return each active user's ID along with the count of their distinct actions. However, I'm getting a count of 0 for some users that I know have actions logged in the `user_actions` table. I've confirmed that the joins are correct and checked the data types for `user_id` in `user_actions` and `id` in `users`. I've also used the following query as a sanity check: ```sql SELECT * FROM user_actions WHERE user_id = 'user_with_no_actions'; ``` This does return records, so I suspect the scenario lies with how DISTINCT interacts with the JOIN. I've also tried removing `DISTINCT` to see if that changes anything, but the counts are still not matching what I expect. Could this scenario be due to null values in the `action` column or some other edge case? What can I do to ensure I'm counting the actions correctly? I'm working on a CLI tool that needs to handle this. I'm working on a CLI tool that needs to handle this. I'd really appreciate any guidance on this. This is happening in both development and production on Debian. Thanks for your help in advance! I'm working on a microservice that needs to handle this. Could someone point me to the right documentation? For reference, this is a production web app. Is there a better approach?