Tutorials › PostgreSQL Essentials › GROUP BY and HAVING

GROUP BY and HAVING

6 min read Quiz at the end

GROUP BY groups rows with the same values so aggregates apply per group. HAVING filters groups after aggregation. Example: find departments with more than 5 employees using GROUP BY and HAVING COUNT(*) > 5.

Grouping Results

-- Sales per city
SELECT city, COUNT(*) AS orders
FROM orders
GROUP BY city;

-- Only cities with 10+ orders
SELECT city, COUNT(*) AS orders
FROM orders
GROUP BY city
HAVING COUNT(*) >= 10
ORDER BY orders DESC;

WHERE filters rows before grouping. HAVING filters after.

← Aggregate Functions Next: JOINs →

Topic Quiz · 5 questions

Test your understanding before moving on

1. Which clause filters after grouping?

💡 HAVING filters groups — like WHERE but applied after GROUP BY.

2. Which clause filters before grouping?

💡 WHERE filters individual rows before they are grouped.

3. What does GROUP BY do?

💡 GROUP BY combines rows with the same column value for aggregation.

4. Can you GROUP BY multiple columns?

💡 You can GROUP BY any number of columns.

5. Which is the correct order?

💡 Correct SQL order: WHERE (filter rows) → GROUP BY (group) → HAVING (filter groups).

Quick Access

GROUP BY and HAVING

Grouping Results

Test your understanding before moving on