Normalize data in SQL query - mysql

Question

I have an SQL query A (see below for more details) that returns a table as following:
cluster brand amount
0 bos 600
0 phi 300
0 har 100
1 pro 2500
1 wal 1500
1 ash 1000
2 dil 4200
2 sor 500
2 van 300
...
However, I want to show not the amount, but the fraction of that amount compared to the total amount in that cluster, like in the following table:
cluster brand amount
0 bos 0.60
0 phi 0.30
0 har 0.10
1 pro 0.50
1 wal 0.30
1 ash 0.20
2 dil 0.84
2 sor 0.10
2 van 0.06
...
How should I change my SQL such that I can get access to the sum over all amounts in one cluster, and still have multiple rows with the same cluster?
** Details **
SQL server: MySQL, interfaced through the python-MySQL connector.
Current SQL query to generate the first table:
SELECT c.cluster, brand, COUNT(o.id) AS brand_amount
FROM nyon_all.clustering AS c
LEFT JOIN nyon_all.persons AS p ON c.pid = p.id
LEFT JOIN nyon_all.orders AS o ON p.id = o.pid
LEFT JOIN nyon_all.articles AS a ON o.aid = a.id
LEFT JOIN nyon_all.brands AS ab ON a.brand_id = ab.id
WHERE c.cluster_round = 'Org_2014-08-27_10:45:35'
GROUP BY cluster, brand
HAVING brand_amount > 100
ORDER BY c.cluster ASC, brand_amount DESC;
Table orders (primary key id) links persons (foreign key pid) with articles (foreign key aid). Articles have a certain brand (foreign key brand_id), which are related to a name in the Table brands.
The total amount of articles per cluster can be retrieved with the following SQL query:
SELECT c.cluster, COUNT(o.pid) AS amount
FROM nyon_all.clustering AS c
LEFT JOIN nyon_all.persons AS p ON c.pid = p.id
LEFT JOIN nyon_all.orders AS o ON p.id = o.pid
WHERE c.cluster_round = 'Org_2014-08-27_10:45:35'
GROUP BY cluster
ORDER BY c.cluster ASC, amount DESC;
Result:
cluster amount
0 1000
1 5000
2 5000
However, I can't seem to combine the two SQL queries.

Answer 1

You could do a join on a subquery summing the amount by cluster
select t1.cluster, amount / sumAmount
from Table1 t1
join (select cluster, sum(amount) as sumAmount
from Table1
group by cluster)s
on t1.cluster = s.cluster
see SqlFiddle
EDIT
SELECT
c.cluster,
brand,
COUNT(o.id) / coalesce(s.sumBrandAmount, 0) AS brand_amount -- of course it would be nice to check for dividing by 0
FROM nyon_all.clustering AS c
LEFT JOIN nyon_all.persons AS p ON c.pid = p.id
LEFT JOIN nyon_all.orders AS o ON p.id = o.pid
LEFT JOIN nyon_all.articles AS a ON o.aid = a.id
LEFT JOIN nyon_all.brands AS ab ON a.brand_id = ab.id
LEFT JOIN (select c1.id, count(o1.id) as sumBrandAmount
from nyon_all.clustering c1
left join nyon_all.persons p1 on p1.id = c1.pid
left join nony_all.orders as o1 on o1.id = p1.id
--maybe some where clause as in your main query
group by c1.id) s
ON s.id = c.id
WHERE c.cluster_round = 'Org_2014-08-27_10:45:35'
GROUP BY cluster, brand
HAVING brand_amount > 100
ORDER BY c.cluster ASC, brand_amount DESC;