Have you ever written complex SQL queries or database queries?

Yes, I have experience writing complex SQL queries in PHP projects. For example, I wrote queries with multiple JOINs to combine data from different tables, used subqueries and aggregate functions.

An example of a complex query to select users with their number of orders:

SELECT u.id, u.name, COUNT(o.id) AS orders_count
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE u.status = 'active'
GROUP BY u.id, u.name
HAVING COUNT(o.id) > 5
ORDER BY orders_count DESC;

In PHP, such a query can be executed using PDO or mysqli, processing the results for further application logic.