Question

我正在尝试回答以下问题，作为Mondial DB的一部分。

-- For each country display the city with the highest population together with the number of the population.

表格是：

国家/地区（代码，姓名，资本，省份，地区，人口）

城市（名称，国家，省，经度，纬度，人口）

到目前为止，我有以下内容：

SELECT 
    Country.Name, MaxCity.CityName, MaxCity.Population
FROM
    (SELECT 
        MAX(Population) AS Population,
            City.Country,
            City.Name AS CityName
    FROM
        City
    GROUP BY City.Country) AS MaxCity
        JOIN
    Country ON Country.Code = MaxCity.Country;

哪里出错了？

Answer 1

以这种方式尝试（我添加了额外的连接）

SELECT 
    Country.Name, City.CityName, City.Population
FROM
    Country Join City On Country.Code = City.Country
Join (SELECT 
        MAX(Population) AS Population,Country as Country from City Group By Country)  as X
On City.Country = x.Country and City.Population = x.Population

Answer 2

在原始查询中，需要按字段city.name

添加分组

    select country.name, maxcity.cityname, maxcity.population
    from
        (select 
            MAX(population) as population,
        city.country,
        city.name as cityname
    from city
    group by city.country, city.name) as maxcity
            join
    country on country.code = maxcity.country

Mondial DB内部查询

2 个答案: