How can I correctly implement a conditional aggregation query in PostgreSQL?
I keep running into I'm a bit lost with I'm converting an old project and I'm working on a personal project and I've searched everywhere and can't find a clear answer... I've been struggling with this for a few days now and could really use some help. I'm trying to create a report that shows the total sales for each product along with the average sale amount, but I want to conditionally filter the sales data based on whether the sales occurred in the last quarter. However, I'm running into issues with my query returning incorrect results. Here’s the SQL I'm currently using: ```sql SELECT product_id, COUNT(*) AS total_sales, AVG(sale_amount) AS average_sale_amount FROM sales WHERE sale_date >= DATE_TRUNC('quarter', CURRENT_DATE) - INTERVAL '3 months' GROUP BY product_id; ``` I expected this to give me the number of sales and average sale amount for each product sold in the last quarter. However, when I run it, the output seems to include sales from earlier quarters as well, which I confirm by checking some sample data. The `sale_date` field is of type `DATE`, and I also verified that there are no issues with the data type. To troubleshoot, I tried adjusting the `WHERE` clause to explicitly check for a date range: ```sql WHERE sale_date >= '2023-07-01' AND sale_date < '2023-10-01' ``` This seems to work correctly, but I want to make sure that my approach is both flexible and maintainable without hardcoding dates. I suspect my scenario might be with how I'm calculating the date range for the last quarter. Any suggestions on how to properly filter the sales data conditionally based on the quarter, or is there a more efficient way to structure the query? I'm using PostgreSQL 13.3. This is part of a larger application I'm building. What's the best practice here? Any pointers in the right direction? I'm working in a Debian environment. I'm open to any suggestions.