How would you assess your SQL skills and your level of query language proficiency?

SQL skills are evaluated based on several criteria: the ability to write basic SELECT queries, use JOIN to combine tables, filter data with WHERE, group with GROUP BY, and sort with ORDER BY. It is also important to understand subqueries, indexes, and query optimization. The proficiency levels can be divided as follows:

• Junior: can write simple queries, perform basic data operations.
• Middle: confidently works with multiple tables, optimizes queries, uses complex constructs.

Example of a simple query:

SELECT users.name, orders.amount
FROM users
JOIN orders ON users.id = orders.user_id
WHERE orders.amount > 100
ORDER BY orders.amount DESC;