Calculate Cumulative Sum (Running Total) Using Window Functions

SELECT
  order_date,
  amount,
  SUM(amount) OVER (ORDER BY order_date) AS running_total_amount
FROM
  orders
ORDER BY
  order_date;

How it works: This query uses a window function, SUM(...) OVER (...), to calculate a running total. For each row, SUM(amount) OVER (ORDER BY order_date) computes the sum of the 'amount' for all rows up to and including the current 'order_date', based on the specified order. This provides a cumulative sum over a sequence of data, which is highly useful for tracking progress, financial balances, or sales trends over time.