Core Code
Core Code Modern Dev Handbook

SQL Group By

GROUP BY groups rows that share the same values and lets you calculate aggregates per group using COUNT, SUM, AVG, MIN, or MAX.
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SQL GROUP BY

The GROUP BY statement groups rows that have the same values into summary rows. It is typically used with aggregate functions such as COUNT(), SUM(), AVG(), MIN(), and MAX().

Basic Syntax

SELECT column_name, AGGREGATE_FUNCTION(column_name)
FROM table_name
GROUP BY column_name;

Example: Count Customers per Country

SELECT country, COUNT(*) AS total_customers
FROM customers
GROUP BY country;

Example: Total Sales per Category

SELECT category, SUM(price * quantity) AS total_sales
FROM order_items
GROUP BY category;

Example: Average Price per Category

SELECT category, ROUND(AVG(price), 2) AS average_price
FROM products
GROUP BY category;

GROUP BY with ORDER BY

ORDER BY is often used to sort grouped results (for example, highest totals first).

SELECT country, COUNT(*) AS total_customers
FROM customers
GROUP BY country
ORDER BY total_customers DESC;

Important Rule

When using GROUP BY, every selected column must either:

  • appear in the GROUP BY clause, or
  • be used inside an aggregate function

Filtering: WHERE vs HAVING

WHERE filters rows before grouping. HAVING filters groups after aggregation.

HAVING is covered in detail in the next lesson.

Example: Filter Before Grouping

SELECT country, COUNT(*) AS total_customers
FROM customers
WHERE status = 'active'
GROUP BY country;

Common Mistakes

  • Selecting non-aggregated columns without adding them to GROUP BY
  • Using WHERE to filter aggregated results (use HAVING instead)
  • Forgetting ORDER BY when you want sorted summary output

Next Step

Continue with SQL HAVING to learn how to filter grouped results.

SQL Having →