Performance Development Tutorials, Guides & Insights

Subqueries can be inefficient as they may require multiple scans of the same table. Use joins or derived tables instead.

-- Subquery
SELECT * FROM users WHERE user_id IN (SELECT user_id FROM orders);

-- Optimized with JOIN
SELECT users.* FROM users
JOIN orders ON users.user_id = orders.user_id;

EXPLAIN SELECT * FROM employees;

Avoid SELECT *: