How to find nearest neighbors between two tables with point locations in SpatiaLite?

Question

I have started playing with SpatiaLite today and already stumbled upon a problem.

For each point location stored in tableOne I would like to select one, nearest (linear distance) point from tableTwo.

So far I came up with a clumsy solution that utilizes VIEW:

CREATE VIEW testview AS 
SELECT 
A.id , 
B.myValue, 
Distance(A.Geometry, B.Geometry) AS distance
FROM tableOne AS A, tableTwo AS B
WHERE distance < 10000
ORDER BY A.Id, distance;

And then:

SELECT * FROM testview
WHERE distance = (SELECT MIN(distance) FROM testview AS t WHERE t.id = testview.id)

seems to do the job.

Two questions:

Is there a way to perform such query without creating a VIEW?

Is there any other way to optimize this query for better performance? In a real world scenario tableOne will have hundreds-couple thousands records, and tableTwo - 1.3 million.

Answer 1

You can simplify your query like this.

SELECT 
   A.id , 
   B.myValue, 
   MIN(Distance(A.Geometry, B.Geometry)) AS distance
FROM tableOne AS A, tableTwo AS B
GROUP BY A.id, B.myValue

For a more generic solution, it might be worth trying to convert this PostGIS Nearest Neighbor function: http://blog.mackerron.com/2011/03/postgis-nearest-neighbour/