sql - 从数据库中删除重复的城市

Question

背景

超过 5300 个重复行:

"id","latitude","longitude","country","region","city"
"2143220","41.3513889","68.9444444","KZ","10","Abay"
"2143218","40.8991667","68.5433333","KZ","10","Abay"
"1919381","33.8166667","49.6333333","IR","34","Ab Barik"
"1919377","35.6833333","50.1833333","IR","19","Ab Barik"
"1919432","29.55","55.5122222","IR","29","`Abbasabad"
"1919430","27.4263889","57.5725","IR","29","`Abbasabad"
"1919413","28.0011111","58.9005556","IR","12","`Abbasabad"
"1919435","36.5641667","61.14","IR","30","`Abbasabad"
"1919433","31.8988889","58.9211111","IR","30","`Abbasabad"
"1919422","33.8666667","48.3","IR","23","`Abbasabad"
"1919420","33.4658333","49.6219444","IR","23","`Abbasabad"
"1919438","33.5333333","49.9833333","IR","34","`Abbasabad"
"1919423","33.7619444","49.0747222","IR","24","`Abbasabad"
"1919419","34.2833333","49.2333333","IR","19","`Abbasabad"
"1919439","35.8833333","52.15","IR","35","`Abbasabad"
"1919417","35.9333333","52.95","IR","17","`Abbasabad"
"1919427","35.7341667","51.4377778","IR","26","`Abbasabad"
"1919425","35.1386111","51.6283333","IR","26","`Abbasabad"
"1919713","30.3705556","56.07","IR","29","`Abdolabad"
"1919711","27.9833333","57.7244444","IR","29","`Abdolabad"
"1919716","35.6025","59.2322222","IR","30","`Abdolabad"
"1919714","34.2197222","56.5447222","IR","30","`Abdolabad"

其他详细信息:

• PostgreSQL 8.4 数据库
• Linux

问题

有些值明显重复(“Abay”是因为区域匹配，“Ab Barik”是因为两个位置非常接近)，其他值则不是那么明显(甚至可能不是实际重复):

"1919430","27.4263889","57.5725","IR","29","`Abbasabad"
"1919435","36.5641667","61.14","IR","30","`Abbasabad"

目标是消除所有重复项。

问题

给定一个值表，例如上述 CSV 数据:

• 您将如何消除重复项？
• 您会使用哪些以地理为中心的 PostgreSQL 函数？
• 您还会使用哪些其他标准来减少重复项？

更新

用于选择同一国家/地区内距离很近(10 公里以内)的重复城市名称的半工作示例代码:

select
  c1.country, c1.name, c1.region_id, c2.region_id, c1.latitude_decimal, c1.longitude_decimal, c2.latitude_decimal, c2.longitude_decimal
from
  climate.maxmind_city c1,
  climate.maxmind_city c2
where
  c1.country = 'BE' and
  c1.id <> c2.id and
  c1.country = c2.country and
  c1.name = c2.name and
  (c1.latitude_decimal <> c2.latitude_decimal or c1.longitude_decimal <> c2.longitude_decimal) and
  earth_distance(
    ll_to_earth( c1.latitude_decimal, c1.longitude_decimal ),
    ll_to_earth( c2.latitude_decimal, c2.longitude_decimal ) ) <= 10
order by
  country, name

想法

两阶段方法:

1. 通过删除 min(id) 来消除明显的重复(相同的国家、地区和城市名称)。
2. 消除彼此非常接近、具有相同名称和国家/地区的那些。这可能会移除一些合法城市，但几乎没有任何后果。

谢谢!

Answer 1

查找重复很简单:

select
  max(id) as this_should_stay,
  latitude,
  longitude,
  country,
  region,
  city
FROM
  your_table
group by
  latitude,
  longitude,
  country,
  region,
  city
having count(*) > 1;

在此基础上添加删除重复项的代码很简单:

delete from your_table where id not in (
    select
      max(id) as this_should_stay
    FROM
      your_table
    group by
      latitude,
      longitude,
      country,
      region,
      city
)

请注意删除查询中缺少 having。