📊 AggregationintermediateCommonly used

How to use GROUP BY in SQL

Group rows with the same value and apply aggregate functions to each group.

Basic GROUP BYAll databases

SELECT
  country,
  COUNT(*) AS user_count
FROM users
GROUP BY country;

Groups all rows by country and counts the users in each group.

GROUP BY multiple columnsAll databases

SELECT
  country,
  active,
  COUNT(*) AS count
FROM users
GROUP BY country, active
ORDER BY country, active;

Groups by every combination of country and active status.

GROUP BY with multiple aggregatesAll databases

SELECT
  status,
  COUNT(*)       AS order_count,
  SUM(total)     AS revenue,
  AVG(total)     AS avg_value,
  MAX(total)     AS largest
FROM orders
GROUP BY status;

Multiple aggregate functions on the same groups.

GROUP BY with JOINAll databases

SELECT
  u.country,
  COUNT(DISTINCT u.id) AS customers,
  SUM(o.total)         AS revenue
FROM users u
INNER JOIN orders o ON u.id = o.user_id
GROUP BY u.country
ORDER BY revenue DESC;

Group revenue by country by joining users to orders first.

Common Mistakes

→Every column in SELECT must either be in GROUP BY or be an aggregate function
→GROUP BY does not sort results — use ORDER BY separately

Common Mistakes

Related Topics