MySQL: guide with DISTINCT and ORDER BY not returning expected results in version 8.0
I'm working with an unexpected behavior in my MySQL 8.0 database when using `DISTINCT` in conjunction with `ORDER BY`. My query is intended to return unique entries based on two columns, but the results seem to be inconsistent. Here’s the SQL I’m working with: ```sql SELECT DISTINCT user_id, created_at FROM user_actions ORDER BY created_at DESC; ``` In theory, this should give me unique records of `user_id` and their latest `created_at` timestamps. However, I noticed that some `user_id`s appear more than once in the output, and the order is not respecting the `created_at` values as expected. I’ve tried breaking down the query, using a subquery to first get the latest `created_at` for each `user_id`: ```sql SELECT user_id, MAX(created_at) as latest_created_at FROM user_actions GROUP BY user_id; ``` This approach works, but I was hoping to achieve the same result without the need for a subquery. I've also checked the data types for both columns, and they seem fine, with `user_id` as an `INT` and `created_at` as a `DATETIME`. Is there something I'm missing with how MySQL handles `DISTINCT` with `ORDER BY`, or is this a known scenario with version 8.0? Any insights or workarounds would be appreciated!