Aggregate Functions

Aggregate functions perform calculations on sets of rows.

Basic Aggregates

-- Count rows
SELECT COUNT(*) FROM users;

-- Count non-null values
SELECT COUNT(email) FROM users;

-- Sum values
SELECT SUM(total) FROM orders;

-- Average
SELECT AVG(age) FROM users;

-- Min and Max
SELECT MIN(price), MAX(price) FROM products;

GROUP BY

-- Group by single column
SELECT country, COUNT(*) as user_count
FROM users
GROUP BY country;

-- Group by multiple columns
SELECT country, city, COUNT(*) as count
FROM users
GROUP BY country, city;

HAVING Clause

-- Filter after aggregation
SELECT country, COUNT(*) as user_count
FROM users
GROUP BY country
HAVING COUNT(*) > 100;

Multiple Aggregates

SELECT
  category,
  COUNT(*) as product_count,
  AVG(price) as avg_price,
  MIN(price) as min_price,
  MAX(price) as max_price
FROM products
GROUP BY category;