[HackerRank] INNER JOIN : Average Population of Each Continent

1. 문제

 

Given the CITY and COUNTRY tables, query the names of all the continents (COUNTRY.Continent) and their respective average city populations (CITY.Population) rounded down to the nearest integer.

 

Note: CITY.CountryCode and COUNTRY.Code are matching key columns.

 

Input Format

The CITY and COUNTRY tables are described as follows: 

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2. 답

SELECT country.continent, FLOOR(AVG(city.population)) 
FROM city
    INNER JOIN country ON city.countrycode = country.code
GROUP BY country.continent

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3. KEY POINT

 

• INNER JOIN : 양쪽 테이블의 모두 있는 정보를 합침
• AVG(컬럼이름) : 해당 컬럼의 평균
• FLOOR() : 내림
• GROUP BY : 기준을 중심으로 그룹화

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Average Population of Each Continent | HackerRank