Calculate a Running Total Using Window Functions

SELECT
    order_date,
    order_id,
    order_total,
    SUM(order_total) OVER (ORDER BY order_date ASC, order_id ASC) AS running_total
FROM
    orders
ORDER BY
    order_date ASC, order_id ASC;

How it works: This query calculates a running total (cumulative sum) of `order_total` for each row, ordered by `order_date` and then `order_id`. The `SUM() OVER (ORDER BY ...)` syntax is a window function that computes an aggregate value for a set of rows related to the current row, without grouping them into a single output row. The `ORDER BY` clause within the `OVER()` specifies the order in which the sum accumulates, creating a cumulative effect.