관련 SQL 쿼리

Question

저는 SQL을 처음 사용합니다. 현재 복잡한 쿼리를 작성하는 법을 배우고 있습니다.

세 개의 테이블이 있습니다. Country-- 국가의 목록이

-----------+------------- 
CountryId | CountryName 
-----------+------------- 
     1 | India 
     2 | Srilanka 
     3 | Pakistan 
     4 | Bangladesh 
     5 | Nepal 
     6 | America 
     7 | Japan 
     8 | China 
     9 | Russia 
     10 | Canada 
     11 | Australia 
--------------------------------------- 

도시 - 국가의 도시 목록

--------+-------------+----------- 
CityId | CityName | CountryId 
--------+-------------+----------- 
     1 | Chennai  |   1 
     2 | Washington |   6 
     3 | Moscow  |   9 
     4 | Tokyo  |   7 
     5 | Beijing  |   8 
     6 | Sydney  |  11 
     7 | Bangalore |   1 
     8 | Nagercoil |   1 
     9 | AmericaCity |   6 
    10 | Kathmandu |   5 
    11 | Dhaka  |   4 
    12 | Lahore  |   3 
-------------------------------------- 

공항 -

AirportId | AirportName | CityId 
-----------+-------------+-------- 
     1 | Airport1 |  1 
     2 | Airport2 |  4 
     3 | Airport3 |  5 
     4 | Airport4 |  1 
     5 | Airport5 |  6 
     6 | Airport6 |  3 
     7 | Airport7 |  5 
     8 | Airport8 |  7 
     9 | Airport9 |  6 
     10 | Airport10 |  3 
     11 | Airport11 |  11 
     12 | Airport12 |  10 
     13 | Airport13 |  12 
--------------------------------- 

이 질문 도시의 공항 목록 : 나는 검색 할 공항 수가 많은 모든 국가 (예 :

)

Output: 
countryName Airports 
India   3 
Srilanka   0 
......... etc. 

이 유용 할 것이다

Answer 1

보십시오 : 그것은

SELECT 
    Country.CountryId, 
    Country.CountryName, 
    count(AirportID) AS Airports 
FROM 
    Country 
    LEFT JOIN city ON Country.CountryId=city.CountryId 
    LEFT JOIN Airport ON city.CityId=Airport.CityId 
GROUP BY Country.CountryId 

Answer 2

select 
    c.CountryName, 
    SUM(
    select count(*) from Airport a 
    inner join City city on city.CityId = a.CityId 
    where city.CountryId = c.CountryId 
    ) as Airports 
from 
    Country c 

Answer 3

SELECT 
    Country.CountryName, 
    count(*) AS Airports 
FROM 
    Country 
    INNER JOIN city ON Country.CountryId=city.CountryId 
    INNER JOIN Airport ON city.CityId=Airport.CityId 
GROUP BY Country.CountryId 

Answer 4

SELECT a.AirportName, co.CountryName, COUNT(co.name) AS count 
FROM Airports as a 
LEFT JOIN City as c ON a.CityId = c.CityId 
LEFT JOIN Country as co ON c.CountryId = co.CountryId 
GROUP BY co.CountryId 

Answer 5

SELECT CountryName, COUNT(CountryName) AS Airports 

FROM Airports INNER JOIN City ON Airports.CityId = City.CityId 
       INNER JOIN Country ON City.CountryId = Country.CountryId 

GROUP BY CountryId 

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