SQL ZOO 练习 —— SELECT within SELECT Tutorial

This tutorial looks at how we can use SELECT statements within SELECT statements to perform more complex queries.
Insert image description here

1.List each country name where the population is larger than that of ‘Russia’.

world(name, continent, area, population, gdp)

SELECT name FROM world
  WHERE population >
     (SELECT population FROM world
      WHERE name='Russia')

2.Show the countries in Europe with a per capita GDP greater than ‘United Kingdom’.

SELECT name FROM world
WHERE continent = 'Europe' AND name IN
   (SELECT name FROM world 
    WHERE gdp/population > 
            (SELECT gdp/population FROM world WHERE name = 'United Kingdom' ) )

3.List the name and continent of countries in the continents containing either Argentina or Australia. Order by name of the country.

SELECT name,continent FROM world 
WHERE continent IN
(SELECT continent FROM world 
WHERE name IN('Argentina ','Australia'))
ORDER BY name

4.Which country has a population that is more than United Kingom but less than Germany? Show the name and the population.

SELECT name, population FROM world 
WHERE population > (SELECT population FROM world WHERE name = 'United Kingdom')
      AND population < (SELECT population FROM world WHERE name = 'Germany')

5.Germany (population 80 million) has the largest population of the countries in Europe. Austria (population 8.5 million) has 11% of the population of Germany.

Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.
The format should be Name, Percentage for example:
Insert image description here

SELECT name,CONCAT(ROUND(100*population/(select population from world where name='Germany'),0),'%')
    FROM world 
    WHERE continent='Europe'

6.Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)

SELECT name
FROM world
WHERE gdp > ALL(SELECT gdp FROM world WHERE gdp>0 AND continent = 'Europe')

7.Find the largest country (by area) in each continent, show the continent, the name and the area:

SELECT continent,name,area
FROM world x
WHERE area = (SELECT MAX(area) FROM world y
WHERE y.continent = x.continent
AND area>0)

8.List each continent and the name of the country that comes first alphabetically.

The first method (conforms to this section, correlated subquery)

SELECT continent,name
FROM world a
WHERE name = 
            (SELECT min(name) FROM world b WHERE a.continent = b.continent )

The second method (combined query), if you don’t understand it, don’t read it first. You will understand it later when you learn the combined query.

SELECT continent,MIN(name)
FROM world 
GROUP BY continent

The third method

select continent, name from world a where name <= all
(select name from world b where a.continent=b.continent)

9.Find the continents where all countries have a population <= 25000000. Then find the names of the countries associated with these continents. Show name, continent and population.

The first

SELECT name,continent,population
FROM world 
WHERE continent NOT IN
                  (SELECT continent
                   FROM world 
                   WHERE population > 25000000)

The second type
is very easy to understand and truly reflects the requirements of the question.

select name,continent,population from world a where 25000000>= all
(select population from world b where a.continent=b.continent)

10.Some countries have populations more than three times that of all of their neighbours (in the same continent). Give the countries and continents.

SELECT name,continent
FROM world x
WHERE population >= ALL(
                        SELECT 3*population FROM world y
                         WHERE y.continent = x.continent
                         AND y.name <> x.name
                         AND population > 0
                       )