Calculate sum of a group without window function

Question

I have a table

Country Population Continent

I am asked to find

For each continent, find the country with largest % of populaiton in every continent.

Sample Output

   Country Population_Rate Continent
    1       30%               A
    2       40%               B

No window function is allowed.No CTE.

I can find the largest population, but I am not sure how to calculate rate (country_population/continent_population).

SELECT *, FROM t t1
WHERE population > ALL(SELECT * FROM t t2 WHERE t1.continent = t2.continent) 
-- find largest population for each continent

Answer 1

The sample data of Popuation_rate = '30%' which looks like a string

It is easier if the sample data looks like 0.3 or even 30

For demo, Imaging the data type is numeric, eg 30 (not 30%)

For each continent, find the country with largest % of populaiton in every continent.

And thanks for your update, your table structure as following:

Country, Population, Continent

SELECT a.Country, a.Population / b.total * 100 AS Population_Rate, a.Continent
FROM tab AS a
JOIN (
    SELECT Continent, SUM(Population) AS total, MAX(Population) AS max_pop
    FROM tab
    GROUP BY Continent
) AS b ON a.Continent = b.continent AND a.Population = b.max_pop

Answer 2

SELECT T.Country, MAX(M.Population_Rate) as Population_Rate, T.Continent
FROM tab T
JOIN
(SELECT tab.Country, tab.Population/tot.Cont_Total*100 as Population_Rate, tab.Continent
    FROM tab 
    JOIN (
       SELECT Continent, SUM(Population) as Cont_Total
       FROM tab
       GROUP BY Continent
    ) AS tot ON tot.Continent=tab.Continent
) AS M
ON M.Continent=T.Continent AND M.Population_Rate=MAX(M.Population_Rate)
GROUP BY M.Continent;