SQL Fundamentals · Aggregation & Grouping · Lesson 16 of 17

Grouping with GROUP BY

Concept

Grouping with GROUP BY

GROUP BY splits rows into groups, such as by category, so an aggregate function can be computed once per group instead of across the whole table.

By the end of this lesson

Explain the core idea behind Grouping with GROUP BY.
Predict output before running a change.
Test one realistic and one unusual input.
Use the result to make the next decision.

How to study this page

1. Read one concept.
2. Change the example.
3. Run, compare, and explain.
4. Complete the challenge below.

ExampleRunnable

SELECT level, COUNT(*) AS total
FROM courses
GROUP BY level;

Try it Yourself »

Self-check before continuing

Without looking at the example, describe what changes when you modify one input in Grouping with GROUP BY. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Write a query that counts how many students exist for each age.

Loading editor…

Console

Output will appear here...