In what situations is it advisable to use nested queries inside SQL commands?

Nested queries (subqueries) in SQL are used when you need to use the result of one query inside another. This is convenient for solving tasks where data depends on calculations or filters performed in another query.

Typical use cases:

• Retrieving records that meet a certain condition, which is calculated dynamically. For example, selecting employees with a salary above the average:

SELECT * FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

• Checking for the existence of related data using EXISTS or IN:

SELECT * FROM orders
WHERE customer_id IN (SELECT id FROM customers WHERE region = 'Europe');

• Updating or deleting records based on the results of another query.

Nested queries help write compact and logical SQL commands, avoiding complex joins or multiple queries from the application.