5 SUM and COUNT

1.

SELECT
  SUM(population)
FROM
  world

2.

SELECT
  DISTINCT(continent)
FROM
  world

3.

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

4.

SELECT
  COUNT(*)
FROM
  world
WHERE
  area >= 1000000

5.

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

6.

SELECT
  continent,
  COUNT(*)
FROM
  world
GROUP BY
  continent

7.

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

8.

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