درس 8 من 9
GROUP BY والدوال التجميعية
GROUP BY يجمع الصفوف التي لها نفس القيم. الدوال التجميعية مثل COUNT() و SUM() و AVG() تحسب قيماً لكل مجموعة.
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;