SQL Fundamentals · Aggregation & Grouping · Lesson 17 of 17
Filtering Groups with HAVING
Concept
Filtering Groups with HAVING
WHERE filters rows before grouping; HAVING filters groups after aggregation, which is why COUNT and other aggregates can appear in a HAVING clause but not in WHERE.
By the end of this lesson
- Explain the core idea behind Filtering Groups with HAVING.
- 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
HAVING COUNT(*) > 2;Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Filtering Groups with HAVING. 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 finds ages shared by more than one student, using GROUP BY and HAVING.
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Console