SQL Server：仅在两个值相同的情况下选择行一次[重复]

Question

我正在开发由IP2Location 提供的OpenSource 和免费数据库，其中列出了来自互联网的大量 IP 地址。

您可以从here下载。

我的主要兴趣不是 IP 地址：我希望每个国家/地区的每个城市都有 1 个地理坐标。

我现在的查询返回双倍：

WITH cte AS
(   
    -- Let's pass rows that have the same latitude and longitude
    SELECT *, ROW_NUMBER() OVER (PARTITION BY latitude, longitude 
                            ORDER BY latitude, longitude) AS rn
    FROM ip2location_db11
    -- Avoid rows without city name
    where city_name != '-'          
)

SELECT
-- These are the only columns I'm interested in from the whole ip2location_db11 database
ROW_NUMBER() OVER (ORDER BY country_code desc,city_name desc) as countdown_order,
latitude,longitude,city_name,country_code
FROM cte
-- Let's take the first row where latitude and longitude are the same
WHERE rn = 1
-- I want to order results by city name
order by countdown_order desc

这很烦人：

每个城市有一个纬度和经度的一行就可以了：我只想在地图上放一个大头针

Answer 1

编辑如果您可以在不同的 country_code 中拥有相同的城市，您只需将其写入分区 by 即可。否则应该是这样的：

WITH cte AS
(   
    -- Let's pass rows that have the same latitude and longitude
    SELECT *, ROW_NUMBER() OVER (PARTITION BY latitude, longitude 
                            ORDER BY latitude, longitude) AS rn
    FROM ip2location_db11
    -- Avoid rows without city name
    where city_name != '-'          
)
,columnsneeded as (

SELECT
-- These are the only columns I'm interested in from the whole ip2location_db11 database
ROW_NUMBER() OVER (ORDER BY country_code desc,city_name desc) as countdown_order,
latitude,longitude,city_name,country_code
FROM cte
-- Let's take the first row where latitude and longitude are the same
WHERE rn = 1
)

Select countdown_order,latitude,longtitude,city_name,country_code 
from(
Select *,ROW_NUMBER() over(partition by city_name order by countdown_order) as rn1 from columnsneeded
)x where rn1 = 1
-- I want to order results by city name
order by countdown_order desc

Answer 2

我不知道，您的第一列 (countdown_order) 是否有任何意义，或者只是该行的唯一标识符...

无论如何，如果您只想拥有一个带有一对坐标的城市/国家，您可能应该使用 GROUP BY 和 AVG() 聚合函数来平均给定城市的坐标...

SELECT AVG(latitude) AS latitude, AVG(longitude) AS longitude, city_name, country_code
FROM ip2location_db11
GROUP BY country_code, city_name
ORDER BY country_code, city_name

Answer 3

您需要做的就是使用按城市分区的ROW_NUMBER（并按任何东西排序:)）并在外部查询中仅采用等于一的那些（您必须环绕您的查询）。试试这个：

SELECT countdown_order,latitude,longitude,city_name,country_code FROM (
    SELECT
    -- These are the only columns I'm interested in from the whole ip2location_db11 database
    ROW_NUMBER() OVER (ORDER BY country_code desc,city_name desc) as countdown_order,
    ROW_NUMBER() OVER (PARTITION BY city_name ORDER BY latitude) rnTofilter,
    latitude,longitude,city_name,country_code
    FROM cte
    -- Let's take the first row where latitude and longitude are the same
    WHERE rn = 1
    -- I want to order results by city name
) a WHERE rnToFilter = 1
order by countdown_order desc