SELECT with multiple PRIMARY KEY - sql

Question

I have 3 table:
nation (name PRIMARY KEY);
city (name PRIMARY KEY, nation REFERENCES nation(name))
overflight (number, city, PRIMARY KEY (number, city))
The overflight table content is something like below:
AA11 city1
AA11 city2
BB22 city1
BB22 city3
etc.
I need to select only overflight that doesn't have city from a certain nation in the city field.
I've tried with:
SELECT number
FROM overflight
JOIN city ON overflight.city = city.name
WHERE overflight.city NOT IN (
SELECT name FROM city WHERE nation = some_nation
)
GROUP BY number;
but it doesn't work because it doesn't list the row of overflight that have city from some_nation but can happen that the same overflight have another row in the table that doesn't have city in some_nation. How can I display only the overflight that doesn't have city in some_nation at all?
Hope that I've explained my problem as clear as possible.
EDIT
This is exact content of overflight table:
AZ 7255 Rome
AZ 7255 Milan
AZ 608 Rome
AZ 608 New York
AA 1 New York
AA 1 Los Angeles
BA 2430 New York
BA 2430 Los Angeles
Suppose that I want to show the overflight that doesn't fly over any city in Italy. I need that the result is like this
AA 1 New York
AA 1 Los Angeles
BB 2430 New York
BB 2430 Los Angeles

Answer 1

Join the tables to get the overflight numbers that do have a city from the nation that you want to exclude and use the operator NOT IN to select all the other oveflights:
SELECT * FROM overflight
WHERE number NOT IN (
SELECT o.number
FROM overflight o INNER JOIN city c
ON o.city = c.name
WHERE c.nation = 'Italy'
)
See the demo.
Results:
number
city
AA 1
New York
AA 1
Los Angeles
BA 2430
New York
BA 2430
Los Angeles