Calculate a Running Total or Cumulative Sum

SELECT
    order_id,
    order_date,
    amount,
    SUM(amount) OVER (ORDER BY order_date, order_id) AS running_total
FROM
    daily_sales
ORDER BY
    order_date, order_id;

How it works: This query calculates a running total (cumulative sum) of `amount` for each row in the `daily_sales` table. The `SUM(...) OVER (ORDER BY order_date, order_id)` is a window function that sums the `amount` of the current row and all preceding rows based on the `order_date` and `order_id`. This is valuable for trend analysis, financial reporting, and tracking cumulative progress over a sequence of events.