Find N Nearest Neighbors for Given Point Using Postgis

Find n Nearest Neighbors for given Point using PostGIS?

Now since PostGIS 2.0, there's a KNN index for geometry types available.
This gives you nearest 5 records with regard to how far they are away from "your location...".

SELECT *
FROM your_table 
ORDER BY your_table.geom <-> "your location..."
LIMIT 5;

See <-> operator in PostgreSQL manual.

Find nearest point using PostGIS

Processing records 1 by 1, in a loop, induces a lot of network traffic to the DB.

Instead, try to update all entries at once, in a single statement (which you can send from the pyton script if you wish).

UPDATE table_a 
SET id_b = (
  SELECT id_b 
  FROM table_b 
  ORDER BY table_b.geom <-> table_a.geom 
  LIMIT 1
)
WHERE id_b IS NULL;

PostGIS: How to find N closest sets of points to a given set?

The answer on how to find the N-closest neighbours in PostGIS are given here:

Postgis SQL for nearest neighbors

To summarize the answer there:

You need to create a geometry object for your points. If you are using latitude, longitude, you need to use 4326.

UPDATE season SET geom = ST_PointFromText ('POINT(' || longitude || ' ' || latitude || ')' , 4326 ) ;

Then you create an index on the geom field

CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometryfield] ); 

Then you get the kNN neightbors:

SELECT *,ST_Distance(geom,'SRID=4326;POINT(newLon newLat)'::geometry) 
FROM yourDbTable
ORDER BY
yourDbTable.geom <->'SRID=4326;POINT(newLon newLat)'::geometry
LIMIT 10;

Where newLon newLat are the query points coordinates.

This query will take advantage of kNN functionality of the gist index (http://workshops.boundlessgeo.com/postgis-intro/knn.html).

Still the distance returned will be in degrees, not meters (projection 4326 uses degrees).

To fix this:

SELECT *,ST_Distance(geography(geom),ST_GeographyFromText('POINT(newLon newLat)') 
FROM yourDbTable
ORDER BY
yourDbTable.geom <->'SRID=4326;POINT(newLon newLat)'::geometry
LIMIT 10;

When you calculate the ST_distance use the geography type. There the distance is always in meters:

http://workshops.boundlessgeo.com/postgis-intro/geography.html

All this functionality will probably need a recent Postgis version (2.0+). I am not sure though.

Check this for reference https://gis.stackexchange.com/questions/91765/improve-speed-of-postgis-nearest-neighbor-query/

EDIT. This covers the necessary steps for one point. For set of points:

SELECT n1.*,n2.*, ST_Distance(n1.geom,n2.geom) 
FROM yourDbTable n1, yourDbTable n2
WHERE n1.setId=1 AND n1.setId=2 //your condition here for the separate sets
AND n1.id<>n2.id // in case the same object belong to 2 sets
ORDER BY n1.geom <->n2.geom
LIMIT 20;

Perform multiple nearest neighbor query by JOIN clause on PostGis in Postgres

You want a LATERAL join, where a subquery can reference a column from an earlier table in the join list.

SELECT * FROM query CROSS JOIN LATERAL 
    (SELECT * FROM data ORDER BY q<->d LIMIT 1) foo;

Find KNN with a geometry data type using POSTGIS in postgresql

You are missing <-> operator which Returns the 2D distance between A and B. Make sure your geom types and SRID are the same.

SELECT ST_Distance(geom, 
       'POINT(178.1375 51.6186)'::geometry) as distance,
       ST_AsText(geom),
       name, id
FROM mylocations
ORDER BY geom <-> 'POINT(178.1375 51.6186)'::geometry limit 10

How to find the nearest point in POSTGIS?

If you are using recent versions of the software, you can quickly find the K nearest neighbors to a point in PostGIS using KNN-GiST techniques. Small values of K are fastest, and 1 is about as small as they get, so this should work very well for you. I've only used KNN-GiST with text trigrams, but I know they work with PostGIS, too -- I just don't know the best page to read to get started with it. A web search for "postgis knn gist" shows lots of likely candidates.

PostGIS: Find nearest point from a list of 3D points

You were really close.

Taking data sample into account, you're doing a lot of SRS transformations to populate your table. So, the stored SRS needs to match the one used in the query as well.

SELECT id, 
  ST_3DDistance(
    geom,
    ST_Transform(
      ST_SetSRID(
        ST_MakePoint(4571547, 5800297, -246,0312),31468),3857)) AS dist
FROM points_list
ORDER BY dist LIMIT 1;

 id |       dist        
----+-------------------
  2 | 6.936250729464996
(1 Zeile)

You can avoid using ST_Transform if you already can provide ST_3DDistance with the coordinates in the SRS 3857.

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