https://medium.com/learning-sql/sql-window-functions-explained-through-4-real-world-examples-91db9972b6bc

https://modern-sql.com/caniuse/qualify

Using a window function, we could add in a new column total_order_amount which represents the total order amount per customer. We could simply write:

SELECT
  date,
  customer,
  order_amount, 
  SUM(order_amount) OVER(PARTITION BY customer) AS total_order_amount
FROM orders
ORDER BY date

the window function SUM(order_amount) OVER(PARTITION BY customer) effectively partitioned our table into different “windows” (one for each customer) and then calculated the total_order_amount for each of these windows. All of this was achieved without using a GROUP BY aggregation, allowing us to retain the same number of rows.