PostgreSQL query with DISTINCT ON not behaving as expected in order clause
I've been working on this all day and I've searched everywhere and can't find a clear answer. I am using PostgreSQL 13.4 and trying to fetch distinct records based on a specific column while ordering the results in a particular way. I used the `DISTINCT ON` clause with an `ORDER BY` clause, but it’s not returning the results I anticipated. Here’s the query I’m running: ```sql SELECT DISTINCT ON (user_id) user_id, created_at, score FROM user_scores ORDER BY user_id, score DESC; ``` I expect to get the latest score for each user, but I’m seeing that for some users I'm getting older scores instead. It appears that the ordering is not working as I thought it would. I also tried adding a secondary order by clause: ```sql ORDER BY user_id, created_at DESC, score DESC; ``` However, the results are still not what I expected. I also checked the data in the `user_scores` table, and it seems consistent. Here’s a sample of the data: | user_id | created_at | score | |---------|---------------------|-------| | 1 | 2023-10-01 10:00:00 | 50 | | 1 | 2023-10-01 09:00:00 | 70 | | 2 | 2023-10-01 11:00:00 | 30 | | 2 | 2023-10-01 08:00:00 | 40 | | 3 | 2023-10-01 12:00:00 | 20 | I’ve ensured that `user_id` is of type `INTEGER` and `created_at` is `TIMESTAMP`. The scores are all integers as well. I’m trying to understand why older scores are being returned for some users. Any insights into how `DISTINCT ON` works with the order clause or what I might be doing wrong? Also, would there be a better approach to achieve this result, perhaps using a subquery? Thanks in advance! Has anyone else encountered this? I'm developing on Ubuntu 20.04 with Sql. Any help would be greatly appreciated!