MySQL: Incorrect results when using GROUP BY with CASE statement in subquery
I've looked through the documentation and I'm still confused about I'm facing an issue with a MySQL query where I am trying to aggregate data using a `GROUP BY` clause combined with a `CASE` statement in a subquery, but the results are not what I expect. The goal is to calculate the total sales for each product category, but it seems like I'm getting duplicate rows in my result set. Here’s the SQL query I am currently using: ```sql SELECT category, SUM(total_sales) AS total_sales FROM ( SELECT p.category, CASE WHEN s.quantity > 10 THEN s.amount * 0.9 -- 10% discount ELSE s.amount END AS total_sales FROM products p JOIN sales s ON p.product_id = s.product_id ) AS subquery GROUP BY category; ``` I’ve tried to run the inner query independently, and it returns the expected data, but when I aggregate it in the outer query, I end up with multiple entries for the same category. The MySQL version I’m using is 8.0.25. I also tried adding `DISTINCT` to the inner query but that doesn’t resolve the duplicate issue. The result set looks something like this: | category | total_sales | |--------------|-------------| | Electronics | 1000 | | Electronics | 1500 | | Furniture | 800 | | Furniture | 700 | As you can see, the `Electronics` and `Furniture` categories have multiple rows when they should only have one row per category. Any insights on how to properly structure this query to get the expected outcome? I’m trying to follow best practices for writing efficient SQL queries, but I must be missing something here. This is for a desktop app running on Debian. Has anyone else encountered this?