문제 link
https://www.hackerrank.com/challenges/asian-population/problem
Code link
https://github.com/JamesJung01/Hackerrank_sql/blob/main/01_Easy/Population_Census.sql
SELECT SUM(CITY.POPULATION) FROM CITY JOIN COUNTRY ON CITY.COUNTRYCODE = COUNTRY.CODE WHERE COUNTRY.CONTINENT = 'Asia';