SQL Server 2019: How to resolve incorrect SUM results when using LEFT JOIN with NULL values
I've been banging my head against this for hours. I'm facing an issue with my SQL query where I'm trying to calculate the total sales amount from a `Sales` table, but the results are incorrect when I join it with the `Products` table. Specifically, I'm using a LEFT JOIN to include all products, even those with no sales. However, when a product has no sales (NULL values), my SUM function seems to ignore these entries, leading to a misleading total. Here's the query I'm currently using: ```sql SELECT p.ProductID, p.ProductName, SUM(s.Amount) AS TotalSales FROM Products p LEFT JOIN Sales s ON p.ProductID = s.ProductID GROUP BY p.ProductID, p.ProductName; ``` When I run the query, I get totals that don't match what I expect. For example, if there are products with no sales, they show up with a NULL for `TotalSales`, which I want to count as 0 in my results instead. So, I've tried using `COALESCE` to convert NULLs to 0, like this: ```sql SELECT p.ProductID, p.ProductName, COALESCE(SUM(s.Amount), 0) AS TotalSales FROM Products p LEFT JOIN Sales s ON p.ProductID = s.ProductID GROUP BY p.ProductID, p.ProductName; ``` But this still returns NULL for products with no sales, rather than 0. I also checked if any of my records in the `Sales` table are actually NULL, but they all seem valid. It seems the SUM function is just not considering these records in the calculation correctly. Does anyone have an idea of what I might be missing or if there's something specific to SQL Server 2019 that affects how LEFT JOIN and SUM work together? I want to make sure that products with no sales appear with a total of 0 instead of NULL. My development environment is Ubuntu. Any ideas what could be causing this?