Subquery Usage

A subquery is a query inside another query. It helps when you want to:

• Filter using aggregated data.
• Compare a value against a dynamic list.
• Create a temporary table for use in your main query.

Use cases include checking which employees work in a particular location or identifying orders above a calculated average.

-- Subquery in WHERE clause
SELECT name
FROM employees
WHERE department_id IN (
    SELECT id 
    FROM departments 
    WHERE location = 'New York'
);