sqlzoo 4.SELECT within SELECT 答案.

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原题链接：https://sqlzoo.net/wiki/SELECT_within_SELECT_Tutorial

其他题解连接：https://blog.csdn.net/aiqiyizz/article/details/109057732

题解对应的是英文版题目。

4 SELECT within SELECT

4.1 Bigger than Russia

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

4.2 Richer than UK

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

4.3 Neighbours of Argentina and Australia

找到洲$\Rightarrow$找到对应洲的国家

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

4.4 Between Canada and Poland

SELECT name, population
FROM world
WHERE population > (
  SELECT population
  FROM world
  WHERE name = 'Canada'
)
AND
population < (
  SELECT population
  FROM world
  WHERE name = 'Poland'
)

以下也为正解（滑稽）

SELECT name, population
FROM world
WHERE 0=1

4.5 Percentages of Germany

找到德国的人口$\Rightarrow$用各种函数拼出答案

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

4.6 Bigger than every country in Europe

SELECT name
FROM world
WHERE gdp > (
  SELECT max(gdp)
  FROM world
  WHERE continent = 'Europe'
  GROUP BY continent
)

4.7 Largest in each continent

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

4.8 First country of each continent (alphabetically)

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

4.9 Difficult Questions That Utilize Techniques Not Covered In Prior Sections

找到每个洲最大值$\Rightarrow$找到最大值符合的洲$\Rightarrow$找到这些洲对应的国家

注意需要添加AS temp1，否则会出现Every derived table must have its own alias。

SELECT name, continent, population
FROM world
WHERE continent IN (
  SELECT continent
  FROM (
    SELECT continent, max(population) AS Mpop
    FROM world
    GROUP BY continent
  ) AS temp1
  WHERE Mpop <= 25000000
)

4.10

被迫使用ALL，不过也不难

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