Kui hästi sa tead SQL-i?

Senior level SQL knowledge requires a deep understanding:

• Basic operations: SELECT, INSERT, UPDATE, DELETE
• Complex queries with JOIN, subqueries, aggregate functions
• Query optimization: indexes, execution plans, performance analysis
• Transactions and isolation levels
• Procedures and triggers in database management systems
• Data normalization and denormalization
• Working with different database management systems and their features

For example, knowing how to write an optimal query with multiple JOINs and aggregate functions:

SELECT c.customer_id, c.name, SUM(o.amount) AS total_spent
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_date >= '2023-01-01'
GROUP BY c.customer_id, c.name
HAVING SUM(o.amount) > 1000
ORDER BY total_spent DESC;

It is also important to be able to analyze execution plans and optimize queries to improve performance.