Cumulative Percentage (Pareto)

Order products by total sales descending and return the running cumulative percentage of total sales, rounded to 2 decimals.

Table schema

Sales(id INT PRIMARY KEY, product VARCHAR(20), amount INT)

Sample data

id | product | amount
1 | Pen | 20
2 | Pen | 30
3 | Book | 150
4 | Bag | 300