COUNT, SUM, AVG, MIN, MAX

-- How many orders do we have?
SELECT COUNT(*) AS total_orders FROM orders;
-- Result: 3

-- How many unique customers placed orders?
SELECT COUNT(DISTINCT user_id) AS active_customers FROM orders;
-- Result: 2

-- Total revenue from all payments
SELECT SUM(amount) AS total_revenue FROM payments;
-- Result: 1599.98

-- Average order value
SELECT ROUND(AVG(total_amount), 2) AS avg_order_value FROM orders;
-- Result: 563.32

-- Price range of products
SELECT
  MIN(price) AS cheapest,
  MAX(price) AS most_expensive,
  AVG(price) AS average_price
FROM products;
-- cheapest: 89.99 | most_expensive: 999.99 | average_price: 563.32

-- Earliest and latest order
SELECT
  MIN(created_at) AS first_order,
  MAX(created_at) AS latest_order
FROM orders;