easiest way to substract in one column and add in other - sql

Question

Basically I'm trying to move existances from one register to another, substracting from the origin point and adding it to the destiny. I have one table of "Stocks" like this:
country city value
AA 01 500
AA 02 400
BB 01 300
CC 01 100
CC 02 1000
CC 03 2000
And I am receiving a document of "movements" with a structure like this:
quantity originCountry originCity endCountry endCity
10 AA 01 CC 01
20 AA 01 BB 02
50 BB 01 CC 03
Is there a way to do this without creating two normalized tables and several queries.
Edit
The answer must be like this:
quantity originCountry originCity endCountry endCity
AA 01 470
AA 02 400
BB 01 250
CC 01 110
CC 02 1020
CC 03 2050
negative number and business rules aren't relevant

Answer 1

try this (isnull is for tsql):
SELECT country, city, value - isnull(p, 0) + isnull(m, 0) as q
FROM Stocks AS s
LEFT JOIN (SELECT originCountry, originCity, Sum(quantity) m FROM movements GROUP BY originCountry, originCity) AS mm
ON originCountry = s.country AND originCity = s.city
LEFT JOIN (SELECT endCountry, endCity, Sum(quantity) p FROM movements GROUP BY endCountry, endCity) AS mp ON
ON endCountry = s.country AND endCity = s.city
For MS ACCESS (add tag next time...):
this should by work:
SELECT country, city, value - Nz(p, 0) + Nz(m, 0) as q
FROM ((Stocks AS s
LEFT JOIN (SELECT originCountry, originCity, Sum(quantity) m FROM movements GROUP BY originCountry, originCity) AS mm
ON (originCountry = s.country AND originCity = s.city))
LEFT JOIN (SELECT endCountry, endCity, Sum(quantity) p FROM movements GROUP BY endCountry, endCity) AS mp ON
ON (endCountry = s.country AND endCity = s.city))
or this ((if you get error then use DSum function):
SELECT country, city, value
- Nz((
SELECT Sum(quantity) m
FROM movements
WHERE originCountry = s.country AND originCity = s.city
), 0) + Nz((
SELECT Sum(quantity) p
FROM movements
WHERE endCountry = s.country AND endCity = s.city
), 0) as q
FROM Stocks AS s