Business Analyst: What is a window function in SQL?

1-- Rank customers by total orders
2SELECT
3  customer_id,
4  SUM(amount) as total,
5  RANK() OVER (ORDER BY SUM(amount) DESC) as rank
6FROM orders
7GROUP BY customer_id;
8
9-- Running total
10SELECT
11  order_date,
12  amount,
13  SUM(amount) OVER (ORDER BY order_date) as running_total
14FROM orders;