HAVING 和 GROUP BY
HAVING and GROUP BY
我要解决的问题如下
For each continent show the continent and number of countries with populations of at least 10 million
世界table是这样的：
World (name, continent, area, population, gdp)
我的查询（未返回正确结果）：
SELECT continent, COUNT(name)
FROM world
GROUP BY continent
HAVING sum(population) >= 10000000
返回正确结果的查询：
SELECT continent, COUNT(name)
FROM world
WHERE population >= 10000000
GROUP BY continent
谁能告诉我为什么我的查询是错误的？
问题是关于国家，而不是大洲，所以你需要在聚合之前进行过滤。
您的查询版本正在回答：
How many countries are in continents whose population is greater than 10,000,000?
问题是：
How many countries in each continent have a population greater than 10,000,000?
这些是不同的问题。我也意识到，对于英语不流利的人来说，初读时差异可能并不明显。
我要解决的问题如下
For each continent show the continent and number of countries with populations of at least 10 million
世界table是这样的：
World (name, continent, area, population, gdp)
我的查询（未返回正确结果）：
SELECT continent, COUNT(name)
FROM world
GROUP BY continent
HAVING sum(population) >= 10000000
返回正确结果的查询：
SELECT continent, COUNT(name)
FROM world
WHERE population >= 10000000
GROUP BY continent
谁能告诉我为什么我的查询是错误的？
问题是关于国家，而不是大洲，所以你需要在聚合之前进行过滤。
您的查询版本正在回答：
How many countries are in continents whose population is greater than 10,000,000?
问题是：
How many countries in each continent have a population greater than 10,000,000?
这些是不同的问题。我也意识到，对于英语不流利的人来说，初读时差异可能并不明显。