Subqueries in SELECT and WHERE
Explore how to write and interpret SQL subqueries within SELECT and WHERE clauses to handle complex, multi-step queries. Understand how nesting queries allows you to compare values across data sets, filter results dynamically, and display related summaries side-by-side. This lesson guides you through practical examples and reflections to build confidence in using subqueries for advanced data analysis and querying logic.
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:
What’s the company’s average salary?
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. ...