Have you ever had to write SQL queries and what complexity?

Yes, I have had to write SQL queries of varying complexity. Mostly, these were queries for data retrieval with multiple conditions, joins, groupings (GROUP BY), and subqueries. For example, for sales analysis, I wrote queries that joined customer, order, and product tables to generate summary reports on revenue for a specific period:

SELECT c.customer_name, SUM(o.amount) AS total_sales
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_date BETWEEN '2023-01-01' AND '2023-03-31'
GROUP BY c.customer_name
ORDER BY total_sales DESC;

I also wrote more complex queries with window functions for trend analysis and data ranking.