What databases have you worked with and how do you rate your SQL query skills?

Worked with relational databases such as PostgreSQL, MySQL, and Microsoft SQL Server, as well as some NoSQL solutions like MongoDB. I assess my SQL proficiency as confident intermediate — I can write complex queries with multiple JOINs, subqueries, aggregations, and window functions. Also familiar with query optimization and indexes.

Example of a simple query with aggregation and grouping:

SELECT department, COUNT(*) AS employee_count
FROM employees
WHERE active = true
GROUP BY department
ORDER BY employee_count DESC;