SQL ZOO练习——SUM and COUNT

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