SQL Server: Unexpected results when using LEFT JOIN with aggregate functions and GROUP BY
I've searched everywhere and can't find a clear answer. I'm working on a SQL Server 2019 database where I need to generate a report combining sales and customer data. However, I'm encountering unexpected results when using a `LEFT JOIN` combined with aggregate functions and `GROUP BY`. My intention was to show the total sales for each customer, including those who haven't made any purchases. Here's the SQL query I've written: ```sql SELECT c.CustomerID, c.CustomerName, SUM(s.SalesAmount) AS TotalSales FROM Customers c LEFT JOIN Sales s ON c.CustomerID = s.CustomerID GROUP BY c.CustomerID, c.CustomerName; ``` While this seems straightforward, I'm getting `NULL` for `TotalSales` for customers who have made purchases, which isn't what I expect. I've verified the `Sales` table and confirmed that there are indeed sales records associated with those customers. I suspect it might have something to do with how the aggregation is handled when combined with `LEFT JOIN`. I've also tried modifying the query by removing the `GROUP BY` clause to see if that changes the output, but Iām still seeing the same results. Additionally, I ensured there are no hidden filters or conditions affecting the `Sales` data. Am I missing something in the aggregation or the join logic? Any insights would be greatly appreciated. This is part of a larger API I'm building. What's the best practice here?