Need to do a group by count of id and at the same time get the total of count without a group by

Question

Need to do a group by count of id and at the same time get the total of count without a group by This is so I can get the total count of the id and check the percentage of each group by category compared to the total count.

-- Its for an oracle sql script

Something like the following is what I currently have:

SELECT
    count(id) as unit_count,
    category
FROM sales
GROUP BY category
ORDER BY count(id) DESC;

SELECT
    count(id) as total_count
FROM sales

I am not sure how to combine the above two

The final result I am looking for is the following:

category	count	percentage_of_total
televisions	100	25%
mobile phones	300	75%

Answer 1

Window functions are calculated after aggregates. This means that SUM(COUNT(*)) OVER () will total up the counts across the entire result set...

SELECT
    category,
    count(id) as unit_count,
    COUNT(*) / SUM(COUNT(*)) OVER () AS percentage_of_all_units
FROM sales
GROUP BY category
ORDER BY count(id) DESC;