Why does my T-SQL query return different results when using GROUP BY with CASE statements?
I'm prototyping a solution and I can't seem to get I'm integrating two systems and I'm stuck on something that should probably be simple..... I'm working on SQL Server 2019 and trying to aggregate data from a sales table. The goal is to count the number of sales categorized by region and status. However, I'm getting unexpected results when using a `CASE` statement within my `GROUP BY` clause. Here's a simplified version of my query: ```sql SELECT CASE WHEN Region = 'North' THEN 'Northern Region' WHEN Region = 'South' THEN 'Southern Region' ELSE 'Other' END AS RegionGroup, COUNT(*) AS SalesCount FROM Sales GROUP BY CASE WHEN Region = 'North' THEN 'Northern Region' WHEN Region = 'South' THEN 'Southern Region' ELSE 'Other' END; ``` The query returns the correct counts, but when I try to add an additional filtering condition using `WHERE`, it starts to show incorrect results. For instance, when I add `WHERE Status = 'Completed'`, the counts for 'Northern Region' drop significantly: ```sql SELECT CASE WHEN Region = 'North' THEN 'Northern Region' WHEN Region = 'South' THEN 'Southern Region' ELSE 'Other' END AS RegionGroup, COUNT(*) AS SalesCount FROM Sales WHERE Status = 'Completed' GROUP BY CASE WHEN Region = 'North' THEN 'Northern Region' WHEN Region = 'South' THEN 'Southern Region' ELSE 'Other' END; ``` I initially thought it was due to the `WHERE` clause filtering rows before aggregation, but even after confirming that there are indeed 'Completed' sales in both regions, the dropped counts don’t match my expectations. Is there something I'm missing about how `GROUP BY` and `CASE` statements interact, especially when filtering on another column? Any guidance would be appreciated! For context: I'm using Sql on Ubuntu. Thanks in advance! For reference, this is a production CLI tool. What's the correct way to implement this? Any pointers in the right direction? I'm using Sql LTS in this project. Has anyone else encountered this?