SQL Server - Incorrect Data Returned When Using COALESCE with a GROUP BY Clause
I'm working on a personal project and I've been struggling with this for a few days now and could really use some help. I am currently experiencing an scenario with a SQL Server 2017 query where I am using the `COALESCE` function in conjunction with a `GROUP BY` clause. My intention is to replace any `NULL` values with a default value before aggregating results, but it seems that the `COALESCE` function is not working as expected in this context. Here’s a simplified version of my query: ```sql SELECT COALESCE(Category, 'Unknown') AS Category, COUNT(*) AS TotalCount FROM Products GROUP BY COALESCE(Category, 'Unknown') ORDER BY TotalCount DESC; ``` When I run this query, I am expecting to see 'Unknown' for any products that do not belong to a specific category. However, some of the results still display `NULL` values, which is not what I anticipated. Additionally, I attempted a few variations such as using `ISNULL` instead of `COALESCE`, but the scenario continues. I have also confirmed that there are indeed rows in the `Products` table where `Category` is `NULL`, so I'm puzzled as to why they are not being counted correctly. I verified that there are no other filters or conditions affecting the results in this part of my code. Could there be any underlying issues with how SQL Server processes the `GROUP BY` clause in combination with `COALESCE`? What might I be missing in this query? Any advice or suggestions would be greatly appreciated! This is part of a larger application I'm building. Any help would be greatly appreciated! I'm working on a service that needs to handle this. What's the best practice here?