advanced patterns when using MySQL's IFNULL in a SELECT query with GROUP BY
I'm experimenting with I'm upgrading from an older version and I've looked through the documentation and I'm still confused about I'm sure I'm missing something obvious here, but I've been banging my head against this for hours....... Quick question that's been bugging me - I'm working with an unexpected behavior when using the `IFNULL` function in a `SELECT` query that also involves `GROUP BY`. I have a table called `sales_data` that stores sales transactions with columns `id`, `product_id`, and `amount`. My goal is to calculate the total sales amount for each product, but I want to display a default value of 0 if there are no sales for a product. Here’s the query I've written: ```sql SELECT product_id, IFNULL(SUM(amount), 0) AS total_sales FROM sales_data GROUP BY product_id; ``` However, I'm getting results that seem incorrect. For products with no sales, the `total_sales` column is showing `NULL` instead of `0`. I expected that `IFNULL(SUM(amount), 0)` would return `0` when `SUM(amount)` is `NULL`. I've tried changing the query to: ```sql SELECT product_id, SUM(IFNULL(amount, 0)) AS total_sales FROM sales_data GROUP BY product_id; ``` But this still doesn't work as intended. Additionally, I've ensured that the `amount` field does not contain any `NULL` values in the table. The dataset has around 10,000 rows, and I’m using MySQL version 8.0.23. When I run the following query: ```sql SELECT product_id, SUM(amount) AS total_sales FROM sales_data GROUP BY product_id; ``` I do get the expected results, but I don't understand why the `IFNULL` function isn't behaving as I anticipated. Is there a specific way that `IFNULL` interacts with `SUM` in the context of grouping? Any insights would be appreciated! Is there a better approach? This is part of a larger service I'm building. This is part of a larger service I'm building. My team is using Sql for this REST API. I'm using Sql LTS in this project. What would be the recommended way to handle this? I'm working in a CentOS environment. Am I missing something obvious?