Understanding Unexpected Results from GROUP BY with CASE in SQL Server 2019
I'm maintaining legacy code that Quick question that's been bugging me - I'm encountering unexpected results when using `GROUP BY` alongside a `CASE` statement in SQL Server 2019. My aim is to categorize sales data into different revenue bands and total the sales for each band. However, the output does not seem to align with my expectations, particularly when handling NULL values in the `revenue` column. Here's a simplified version of my query: ```sql SELECT CASE WHEN revenue IS NULL THEN 'Unknown' WHEN revenue < 1000 THEN 'Low' WHEN revenue BETWEEN 1000 AND 5000 THEN 'Medium' ELSE 'High' END AS RevenueBand, COUNT(*) AS TotalSales FROM Sales GROUP BY CASE WHEN revenue IS NULL THEN 'Unknown' WHEN revenue < 1000 THEN 'Low' WHEN revenue BETWEEN 1000 AND 5000 THEN 'Medium' ELSE 'High' END; ``` In my dataset, I have several NULL values in the `revenue` column, but when I run the query, I get an output that does not include the 'Unknown' band at all. Instead, I get counts for 'Low', 'Medium', and 'High', which makes me wonder if the NULL values are being excluded from the aggregation. I've checked the dataset and confirmed that there are indeed NULL entries. I've also tried using `ISNULL(revenue, 0)` to convert NULLs to 0s, but that leads to all NULLs being categorized into 'Low', which is not what I want. I would appreciate any insights into why the NULL entries are not being counted in the `Unknown` band and how to properly include them in the results. Is there a specific best practice for handling such cases when using `GROUP BY` with a `CASE` statement? Thanks in advance! For context: I'm using Sql on Windows. Thanks in advance! This is happening in both development and production on Debian. Any feedback is welcome!