How would you rate your SQL skills?

SQL skills can be assessed by the ability to write queries of varying complexity: from simple SELECT statements with filtering to complex JOINs, subqueries, and aggregations. It is also important to understand query optimization, indexes, and transactions.

Example of a simple query to select users over 18 years old:

SELECT id, name, email FROM users WHERE age > 18 ORDER BY name;

For intermediate level, it is desirable to be able to work with multiple tables, use grouping, and aggregate functions:

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;