Lektion 8 af 9
GROUP BY og aggregater
GROUP BY grupperer rækker med samme værdier. Aggregatfunktioner som COUNT(), SUM() og AVG() beregner værdier for hver gruppe.
SQL
-- Count users per country
SELECT country, COUNT(*) as total_users
FROM users
GROUP BY country;
-- Average price per category
SELECT category, AVG(price) as avg_price
FROM products
GROUP BY category;
-- Having filters groups (like WHERE for groups)
SELECT country, COUNT(*) as total
FROM users
GROUP BY country
HAVING total > 10;