SELECT co.continent, floor(avg(ci.population)) from country co INNER join city ci on co.code = ci.countrycode group by co.continent;

SELECT country.continent, floor(avg(city.population)) AS avg_population FROM CITY INNER JOIN country ON city.countrycode = country.code GROUP BY country.continent;

My solution used LEFT JOIN with COUNTRY as the left table and COALESCE to handle NULLs, so it actually included all continents as the problem stated. The accepted INNER JOIN solution only shows 5 out of 7 continents, which doesn’t seem like 'all' continents to me.

SELECT CO.CONTINENT, COALESCE(ROUND(AVG(C.POPULATION), 0), 0)
FROM COUNTRY AS CO
LEFT JOIN CITY AS C
    ON C.COUNTRYCODE = CO.CODE
GROUP BY CO.CONTINENT;

SELECT B.CONTINENT,FLOOR(AVG(A.POPULATION)) AS PROMEDIO FROM CITY A INNER JOIN COUNTRY B ON A.COUNTRYCODE = B.CODE GROUP BY B.CONTINENT ORDER BY PROMEDIO DESC;

MS Sql -

select c.continent , round(avg(ci.population),2) from country c inner join city ci on c.code = ci.countrycode group by c.continent;