Question

尝试编写一个查询，该查询将提供该国家/地区的名称以及该国家/地区所拥有的地区数量以及从最高到最低的地区数量。问题是我无法弄清楚如何具体计算每个国家的地区数量，最终获得一个国家旁边的地区总数，而不是别的...

这两个表是Country（包含Name，Code）和City（包含Name，District，CountryCode）。

Country.Code和City.CountryCode是相同的，这就是两个表的共同点。

非常感谢任何帮助！

Answer 1

 SELECT Name, noofdistricts
   FROM 
      (  SELECT c.Name,COUNT( ci.District ) AS noofdistricts
           FROM Country c
           JOIN City ci
             ON c.code = ci.countrycode
          GROUP BY c.Name
       ) Z
 ORDER BY Name,noofdistricts DESC
 ;

Answer 2

然后执行JOIN，然后执行GROUP BY

select c.Name,
count(cc.District) as total_district
from country c join city cc on c.code = cc.CountryCode 
group by c.Name
order by total_district desc;

Answer 3

如果我理解正确，您正在寻找类似的东西（根据City表中的信息计算一个国家/地区有多少个独特区域）：

select
  districts.country_name as country_name,
  count(districts.district) as district_count
from (      
  select unique --we want to count how many unique districts are there in a given country
    country.code as country_code,
    country.name as country_name,
    city.district as district --we want to get districts where cities are located
  from 
    Country country,
    City city
  where city.CountryCode = country.Code --join cities to countries
) districts
group by districts.country_code
order by district_count desc

SQL查询：每个国家/地区的区数？

3 个答案: