What was your most complex or extensive database query that you created?

One of the most complex database queries I have created was related to sales analytics over several years with many conditions and aggregates.

Example: a query that collected sales data, grouped it by regions and products, considered time intervals, filtered by order status, and included subqueries to calculate averages and rankings.

A simplified example of an SQL query:

SELECT region, product_id, SUM(quantity) AS total_quantity, AVG(price) AS avg_price
FROM sales
WHERE order_status = 'completed'
  AND sale_date BETWEEN '2022-01-01' AND '2023-01-01'
GROUP BY region, product_id
HAVING SUM(quantity) > 100
ORDER BY total_quantity DESC;

In a real project, the query was much more complex, with multiple JOINs, window functions, and optimizations for fast execution on large volumes of data.