CODEWITHSUNDEEP
sqlpostgresqlgeolocationcountrycity
Dave Jarvis
Dave Jarvis

Reputation: 31171

Eliminate duplicate cities from database

Background

Over 5300 duplicate rows:

"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"

Additional details:

Problem

Some values are obvious duplicates ("Abay" because the regions match and "Ab Barik" because the two locations are within such close proximity), others are not so obvious (and might not even be actual duplicates):

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

The goal is to eliminate all duplicates.

Questions

Given a table of values such as the above CSV data:

Update

Semi-working example code to select duplicate city names within the same country that are in close proximity (within 10 km):

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

Ideas

Two phase approach:

  1. Eliminate the obvious duplicates (same country, region, and city name) by removing the min(id).
  2. Eliminate those within close proximity of each other, having the same name and country. This could remove some legitimate cities, but hardly any of consequence.

Thank you!

Upvotes: 1

Views: 1751

Answers (3)

Dave Jarvis
Dave Jarvis

Reputation: 31171

This deletes the second city within close proximity to a city of the same name in the same country:

delete from climate.maxmind_city mc where id in (
select
  max(c1.id)
from
  climate.maxmind_city c1,
  climate.maxmind_city c2
where
  c1.id <> c2.id and
  c1.country = c2.country and
  c1.name = c2.name and
  earth_distance(
    ll_to_earth( c1.latitude_decimal, c1.longitude_decimal ),
    ll_to_earth( c2.latitude_decimal, c2.longitude_decimal ) ) <= 35
group by
  c1.country, c1.name
order by
  c1.country, c1.name
)

Upvotes: 1

user80168
user80168

Reputation:

Finding duplicates is simple:

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;

Adding code to remove duplicates based on this is simple:

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
)

note lack of having in the delete query.

Upvotes: 1

Chandresh M
Chandresh M

Reputation: 3828

if your data have been imported thru CSV files and with the code (PHP) then you can prevent duplicates entry with the putting condition in PHP code. if the city you inserted is already exist then make loop continue to next record and skip current record.

try this if you are follow this way to import data in database..

Thanks.

Upvotes: 0

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