1.展示世界的總人口。
SELECT sum(population)
FROM world
2.列出所有的洲份, 每個只有一次。
select distinct continent
from world
3.找出非洲(Africa)的GDP總和。
select sum(gdp)
from world
where continent='africa'
4.有多少個國家具有至少百萬(1000000)的面積。
select count(name)
from world
where area>1000000
5.('France','Germany','Spain')（“法國”，“德國”，“西班牙”）的總人口是多少？
select sum(population)
from world
where name in ('france','germany','spain')
6.對於每一個洲份，顯示洲份和國家的數量。
select continent,count(name)
from world
group by continent
7.對於每一個洲份，顯示洲份和至少有1000萬人(10,000,000)口國家的數目。
select continent,count(name)
from world
where population>=10000000
group by continent
8.列出有至少100百萬(1億)(100,000,000)人口的洲份。
select continent
from world
group by continent
having sum(population)>=100000000