aggregation

-- ROW_NUMBER: Unique sequential number
SELECT
  name,
  department,
  salary,
  ROW_NUMBER() OVER (ORDER BY salary DESC) as overall_rank,

-- ROLLUP for hierarchical subtotals
SELECT
  COALESCE(category, 'ALL CATEGORIES') AS category,
  COALESCE(subcategory, 'ALL SUBCATEGORIES') AS subcategory,
  SUM(revenue) AS total_revenue,
  COUNT(*) AS order_count