SELECT 
  customer_id,
  COUNT(*) as order_count
 FROM orders
 GROUP BY customer_id
 ORDER BY order_count DESC;

SELECT 
  category,
  COUNT(*) as transaction_count,
  SUM(amount) as total_sales,
  ROUND(AVG(amount), 2) as avg_sale,
  MIN(amount) as min_sale,
  MAX(amount) as max_sale
 FROM sales
 GROUP BY category;

SELECT 
  YEAR(order_date) as year,
  QUARTER(order_date) as quarter,
  SUM(total) as revenue,
  COUNT(*) as order_count
 FROM orders
 GROUP BY YEAR(order_date), QUARTER(order_date)
 ORDER BY year, quarter;

SELECT 
  customer_id,
  COUNT(*) as order_count,
  SUM(total) as total_spent
 FROM orders
 GROUP BY customer_id
 HAVING COUNT(*) > 5 AND SUM(total) > 1000
 ORDER BY total_spent DESC;

SELECT 
  c.category_name,
  COUNT(DISTINCT o.id) as orders,
  SUM(oi.quantity) as units_sold,
  SUM(oi.quantity * oi.price) as revenue
 FROM order_items oi
 INNER JOIN products p ON oi.product_id = p.id
 INNER JOIN categories c ON p.category_id = c.id
 INNER JOIN orders o ON oi.order_id = o.id
 WHERE o.status = 'completed'
 GROUP BY c.category_id, c.category_name
 ORDER BY revenue DESC;

SELECT 
  COALESCE(region, 'TOTAL') as region,
  COALESCE(product, 'Subtotal') as product,
  SUM(sales) as total_sales
 FROM sales_data
 GROUP BY ROLLUP(region, product);

SELECT 
  region,
  product,
  SUM(sales) as total_sales
 FROM sales_data
 GROUP BY CUBE(region, product);