MySQL query with multiple GROUP BY clauses returning unexpected row counts in CodeIgniter 4
I'm facing an issue where my MySQL query with multiple `GROUP BY` clauses is returning unexpected row counts when executed in my CodeIgniter 4 application. I have a `sales` table that contains fields for `id`, `product_id`, `quantity`, and `sales_date`. I want to aggregate the data to get the total quantity of sales per product for each month. Here's the SQL query I tried: ```sql SELECT product_id, MONTH(sales_date) as month, SUM(quantity) as total_quantity FROM sales WHERE YEAR(sales_date) = 2023 GROUP BY product_id, month ORDER BY month; ``` While I expect to see a row for each product for each month, I am getting fewer rows than expected. For instance, if there are no sales for a specific product in a month, that product does not appear at all in the result set. I tried using `LEFT JOIN` with a subquery to include products with zero sales, but the result is still not as expected: ```sql SELECT p.id as product_id, m.month, IFNULL(s.total_quantity, 0) as total_quantity FROM products p CROSS JOIN (SELECT DISTINCT MONTH(sales_date) as month FROM sales WHERE YEAR(sales_date) = 2023) m LEFT JOIN ( SELECT product_id, MONTH(sales_date) as month, SUM(quantity) as total_quantity FROM sales WHERE YEAR(sales_date) = 2023 GROUP BY product_id, month ) s ON p.id = s.product_id AND m.month = s.month ORDER BY m.month, p.id; ``` This approach gives me the correct number of rows, but the total quantity is inaccurate for months where sales exist. I also tried ensuring that my database has the correct indexes on `sales_date` and `product_id`, but that didn't seem to help. Any insights on how to correctly structure this query to get the desired results? Am I missing something in the logic or the SQL syntax? Thanks for any help you can provide!