SUM_and_COUNT

--Table: world(name, continent, area, population, gdp)

--1. Show the total population of the world.

SELECT SUM(population)
 FROM world;

--2. List all the continents - just once each.

SELECT DISTINCT continent
 FROM world;

--3. Give the total GDP of Africa.

SELECT SUM(gdp)
 FROM world
 WHERE continent ='Africa';

--4. How many countries have an area of at least 1000000.

SELECT COUNT(name)
 FROM world
 WHERE area>=1000000;

--5. What is the total population of ('Estonia', 'Latvia', 'Lithuania').

SELECT SUM(population)
 FROM world
 WHERE name IN ('Estonia', 'Latvia', 'Lithuania');

--6. For each continent show the continent and number of countries.

SELECT continent, COUNT(name)
FROM world
GROUP BY continent;

--7. For each continent show the continent and number of countries with populations of at least 10 million.

SELECT continent, COUNT(name)
 FROM world
 WHERE population>=10000000
GROUP BY continent;

--8. List the continents that have a total population of at least 100 million.

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