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Learn SQL in the Age of AI

Subqueries in SELECT and WHERE

Learn how nested queries work in SQL.

We'll cover the following...

Step 1: Start with a question

You already know how to ask questions like: Show the average salary for each department.

But what if you want to ask something relative, like: Which employees earn more than the company average salary?

That requires two questions at once:

  1. What’s the company’s average salary?

  2. Which employees earn more than that value?

A subquery lets you nest one question inside another.

Prompt: Write a SQL query that shows employees whose salary is greater than the company’s average salary.

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Step 2: Run and observe

AI might return:

MySQL
SELECT first_name,
       last_name,
       salary
FROM employees
WHERE salary > (
    SELECT AVG(salary)
    FROM employees
);

 Run it. Now your main query (SELECT ...