SQL GROUP BY and SUM

Question

List the continents with total populations of at least 100 million.

World Table

name         continent  area    population  gdp
Afghanistan  Asia       6522         


        

Answer 1

I'll give you a good framework for thinking through this question.

Since there are multiple records with the same continent, we know we need GROUP BY. Once we do group by, we can use aggregate operations to get the sum, namely SUM. By using this aggregate operation, we can filter using the HAVING clause post group-by. If we wanted to filter pre-groupby, we would use the WHERE clause.

SELECT continent FROM world GROUP BY continent HAVING SUM(population) > 
100000000;

Answer 2

SELECT   continent, SUM(population)
FROM     world
GROUP BY continent
HAVING   SUM(population) >= 100000000