What is a subquery in SQL?

Can you explain what a subquery is in SQL?

Sure! A subquery is a query nested inside another SQL query. It can be used to retrieve data that will be used in the main query.

How do I write a subquery in a SELECT statement?

You can write a subquery in a SELECT statement by placing it in parentheses. For example: SELECT * FROM employees WHERE department_id IN (SELECT id FROM departments WHERE name = 'Sales');

Are there different types of subqueries?

Yes, there are mainly two types: correlated subqueries, which depend on the outer query, and non-correlated subqueries, which can be executed independently.

Can you give me an example of a correlated subquery?

Certainly! Here's an example: SELECT e.name FROM employees e WHERE e.salary > (SELECT AVG(salary) FROM employees WHERE department_id = e.department_id);