SQL dividing numbers by different group by results - mysql

Question

Basically I have a table with several columns but I'm only interested in 4. My table looks like this:
accountID productID profit cost date country city quantity
2 10 25 15 2017/03/13 Afghanistan Kabul 330
18 3 45 42 2017/05/14 UK London 5300
25 14 22 17 2017/05/21 UK London 300
3 11 30 26 2017/04/23 Afghanistan Herat 400
What I want to achieve is to get the total quantity of products by city, by country and the ratio of city_quantity/country_quantity:
country city city_quantity country_quantity city_percentage
Afghanistan Kabul 800 1400 0.57
Afghanistan Kandahar 400 1400 0.29
Afghanistan Herat 200 1400 0.14
UK London 6500 10000 0.65
UK Manchester 3000 10000 0.3
UK Newcastle 500 10000 0.05
So far my script looks like this:
select country, city, sum(quantity)
from table
where date > dateadd(month,-1,getdate())
group by country, city
order by country, city
The where condition is because I only want the last month of data so consider it irrelevant.
How can I achieve what I want with a simple script?

Answer 1

You can do this using a self-join to sum the quantity grouped by country and then use that value to come up with the percentage like so:
CREATE TABLE testTable (country VARCHAR(2), city CHAR(1), quantity DECIMAL(10,2));
INSERT INTO testTable (country, city, quantity)
VALUES
('Af', 'K', 330),
('Af', 'H', 400),
('Af', 'Q', 700),
('UK', 'L', 1000),
('UK', 'M', 500);
SELECT t.country, t.city, t.quantity AS city_quantity, q.qty AS country_quantity,
CAST(t.quantity / q.qty AS DECIMAL(10,2)) AS city_percentage
FROM testTable t
JOIN
(
SELECT z.country, SUM(z.quantity) qty
FROM testTable z
GROUP BY z.country
) q ON t.country = q.country
This will give you the desired results set:
+---------+------+--------------+-----------------+-----------------+
| country | city | city_quantity| country_quantity| city_percentage |
+---------+------+--------------+-----------------+-----------------+
| Af | K | 330 | 1430 | 0.23 |
| Af | H | 400 | 1430 | 0.28 |
| Af | Q | 700 | 1430 | 0.49 |
| UK | L | 1000 | 1500 | 0.67 |
| UK | M | 500 | 1500 | 0.33 |
+---------+------+--------------+-----------------+-----------------+
Keep in mind that you'll want to check for division by zero in any production query.