Tell us about your experience creating SQL queries. What are the most complex queries you have written?

In my practice, I have often created SQL queries of varying complexity — from simple selections to complex analytical queries with multiple levels of nested subqueries and joins.

The most complex queries I have written include:

• Multi-step JOINs with several tables to obtain aggregated data on business processes.
• Use of window functions (e.g., ROW_NUMBER(), RANK()) for ranking and data analysis.
• Recursive CTE queries for working with hierarchical structures.

An example of a complex query with a window function:

SELECT employee_id, department_id, salary,
       RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) as salary_rank
FROM employees
WHERE hire_date > '2020-01-01';

This query allows ranking employees by salary within each department, which is useful for analysis and decision-making.