[HackerRank] Average Population of Each Continent (MySQL)

https://www.hackerrank.com/challenges/average-population-of-each-continent/problem?isFullScreen=true 

Average Population of Each Continent | HackerRank

 

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: 

 

풀이

select c2.continent, floor(avg(c1.population))
from city c1, country c2
where c1.countrycode = c2.code
group by c2.continent