How to implement guide with case statement in sql server causing unexpected results in group by
I've spent hours debugging this and I'm working with an scenario with a query in SQL Server where I'm using a `CASE` statement in conjunction with `GROUP BY`. The intention is to categorize data into 'High', 'Medium', and 'Low' based on a numeric score, but the results are not grouped as expected. Here's the SQL I wrote: ```sql SELECT CASE WHEN score >= 80 THEN 'High' WHEN score >= 50 THEN 'Medium' ELSE 'Low' END AS ScoreCategory, COUNT(*) AS Count FROM Students GROUP BY CASE WHEN score >= 80 THEN 'High' WHEN score >= 50 THEN 'Medium' ELSE 'Low' END; ``` When I run this, I get the expected counts for each category, but the question arises when I add a `WHERE` clause to filter out scores below a certain threshold, like so: ```sql SELECT CASE WHEN score >= 80 THEN 'High' WHEN score >= 50 THEN 'Medium' ELSE 'Low' END AS ScoreCategory, COUNT(*) AS Count FROM Students WHERE score > 30 GROUP BY CASE WHEN score >= 80 THEN 'High' WHEN score >= 50 THEN 'Medium' ELSE 'Low' END; ``` After adding the `WHERE` clause, the counts for 'Low' category disappear completely, which is expected since we filtered out scores below 30. However, I still see unexpected behavior in the counts for 'Medium' and 'High' categories. Specifically, the count for 'Medium' is much lower than anticipated, and I suspect it may be related to how SQL Server is processing the `CASE` statement within the `GROUP BY`. I've tried simplifying the query by breaking it up into subqueries and using Common Table Expressions (CTEs), but the behavior remains the same. The version of SQL Server Iām using is 2019. Any insights on why this might be happening or how I could get consistent results would be greatly appreciated!