How do you improve the performance of slow SQL queries?

To improve the performance of slow SQL queries, I usually:

• Analyze the query execution plan to identify bottlenecks.
• Add or optimize indexes on frequently used columns.
• Rewrite queries to avoid redundant JOINs or subqueries.
• Use LIMIT and pagination if possible.
• Cache results if data doesn't change often.

Example of optimization:

-- Before:
SELECT * FROM orders WHERE customer_id IN (SELECT id FROM customers WHERE region = 'EU');

-- Optimized with JOIN:
SELECT o.* FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.region = 'EU';

This approach often improves performance by more efficiently utilizing indexes.