aggregation

Agregat funksiyalar ko‘p qatorni bitta qiymatga aylantiradi.

SELECT COUNT(*) FROM students;                  -- qatorlar soni
SELECT AVG(grade), MAX(grade), MIN(grade) FROM students;
SELECT SUM(price * qty) AS revenue FROM order_items;
SELECT ROUND(AVG(grade), 2) FROM students;      -- 2 xonagacha yaxlitlash

Diqqat

• GROUP BY siz agregat butun jadval uchun bitta qator qaytaradi.
• Agregat bilan birga oddiy ustun tanlash (SELECT name, MAX(grade)) — GROUP BY siz noaniq natija beradi.
• Butun sonlarni bo‘lishda butun natija chiqishi mumkin: AVG yoki 1.0 * a / b ishlating.