What practice covers
The practice system supports SELECT, filters, sorting, joins, aggregation, subqueries, schema inspection, data changes, views, transactions, and performance-oriented queries.
Beginner exercises block unsafe SQL where needed. Later modules deliberately introduce safe INSERT, UPDATE, DELETE, CREATE, DROP, and transaction workflows.
SELECT c.customer_name, SUM(oi.quantity * oi.unit_price) AS revenue
FROM customers c
JOIN orders o ON o.customer_id = c.customer_id
JOIN order_items oi ON oi.order_id = o.order_id
GROUP BY c.customer_name
ORDER BY revenue DESC;
Correct. 8 rows returned.