How to Use Aggregate Functions in SQL

CREATE TABLE sales (
  id INTEGER PRIMARY KEY,
  product TEXT,
  amount REAL,
  region TEXT
);

INSERT INTO sales VALUES 
  (1, 'Laptop', 999, 'North'),
  (2, 'Mouse', 30, 'South'),
  (3, 'Laptop', 999, 'East'),
  (4, 'Desk', 300, 'North'),
  (5, 'Mouse', 30, 'North'),
  (6, 'Monitor', 450, 'South'),
  (7, 'Desk', 300, 'East'),
  (8, 'Laptop', 999, 'West');

-- Aggregate functions
SELECT 
  COUNT(*) as total_sales,
  SUM(amount) as total_revenue,
  ROUND(AVG(amount), 2) as avg_sale,
  MIN(amount) as smallest,
  MAX(amount) as largest
FROM sales;

-- GROUP BY
SELECT product, COUNT(*) as sales, SUM(amount) as revenue
FROM sales
GROUP BY product
ORDER BY revenue DESC;