Sort partitions and rows inside the partitions - postgresql

Question

I am following this tutorial:
http://www.postgresqltutorial.com/postgresql-window-function/
I'm looking for a case that is not described in the tutorial and I don't found a solution.
At one moment on the tutorial, this SELECT query is used to display the products grouped by group name and their prices sorted ascending in each group, here is the result :
the request is :
SELECT
product_name,
group_name,
price,
ROW_NUMBER () OVER (
PARTITION BY group_name
ORDER BY
price
)
FROM
products
INNER JOIN product_groups USING (group_id);
I would like to sort the rows by price like in the example AND to sort the partition by descending alphabetical order, like this :
How can modify the request to obtain this result ?

Answer 1

ORDER BY can be followed by a comma-separated list of sort_expressions. Use ASC or DESC to set the sort direction for each expression. ASC (ascending order) is the default sort direction.
Thus, you could use ORDER BY group_name DESC, price:
SELECT
product_name,
group_name,
price,
ROW_NUMBER () OVER (
PARTITION BY group_name
ORDER BY
group_name DESC, price
)
FROM
products
INNER JOIN product_groups USING (group_id);
yields
| product_name | group_name | price | row_number |
|--------------------+------------+---------+------------|
| Kindle Fire | Tablet | 150.00 | 1 |
| Samsung Galaxy Tab | Tablet | 200.00 | 2 |
| iPad | Tablet | 700.00 | 3 |
| Microsoft Lumia | Smartphone | 200.00 | 1 |
| HTC One | Smartphone | 400.00 | 2 |
| Nexus | Smartphone | 500.00 | 3 |
| iPhone | Smartphone | 900.00 | 4 |
| Lenovo Thinkpad | Laptop | 700.00 | 1 |
| Sony VAIO | Laptop | 700.00 | 2 |
| Dell Vostro | Laptop | 800.00 | 3 |
| HP Elite | Laptop | 1200.00 | 4 |