BigQuery ST_DWITHIN 多点与多点

Question

So I've got N points to consider and M points for reference. I'm trying to filter all the Points in N, that are within some radius R of any of the M points.

For the following example, my-table-1 is a table with ids and single coordinate GEOGRAPHY entries

Currently im only able to get this working for N to 1 Point using something like this:

SELECT *
FROM 'my-table-1' as one
WHERE ST_DWITHIN(points, (SELECT points FROM 'my-table-1' WHERE id = '1234'), 10000)

So basically what im trying to accomplish is that same statement but using multiple points to compare. What I want is basically this:

SELECT *
FROM 'my-table-1' as one
WHERE ST_DWITHIN(points, (SELECT points FROM 'my-table-1' WHERE id IN('1234', '2345', ...)), 10000)

But this results in a error because ST_DWITHIN can only compare 1 point to N points. I tried looking into BQ LOOPS and ARRAYS but couldnt figure out a solution so far. The exact error im getting in the second statement is Scalar subquery produced more than one element

Basically comparing all points with a set of specific points in the same table and check if they are within some radius around those

Answer 1

I'm trying to filter all the Points in N, that are within some radius R of any of the M points.

The way to work with two tables is via JOIN. Your query

SELECT *
FROM 'my-table-1' as one
WHERE ST_DWITHIN(points, (SELECT points FROM 'my-table-1' WHERE id IN ...), 10000)

Should become

SELECT one.id, one.points
FROM 'my-table-1' one JOIN 'my-table-1' two
ON ST_DWITHIN(one.points, two.points, 10000)
WHERE two.id IN ('1234', '2345', ...)

Note this will produce duplicate points, if some point from one is within 10km of several points in two . So you'll probably want to remove duplicates, I would add GROUP BY for this (this assumes we have some unique column id ):

SELECT id, ANY_VALUE(points) AS points
FROM (
  SELECT one.id, one.points
  FROM 'my-table-1' one JOIN 'my-table-1' two
  ON ST_DWITHIN(one.points, two.points, 10000)
  WHERE two.id IN ('1234', '2345', ...)
)
GROUP BY id

Answer 2

If I understand the case correctly I would probably:

• Create a buffer with radius R around the M points (ST_Buffer)
• Union those geometries (ST_Union)
• Select from the N points using ST_DWithin on the N points and the union/buffer geometry

This is from the top of my head, I can't construct the query in my mind though, but I think a single query should do it or you could throw a WITH statement there.

Let me know if that works for you. I saw that for BigQuery you have no ST_Buffer, but you can use jslibs.turf.ST_BUFFER instead.

Edit: Damn, I just realized this is not a PG question, but a BQ question... Shame on me. Are those functions available there?

Here's an example PG query (tested):

select n.id from "N_Points" as n, (select st_buffer(m.geom, 20000) as geom 
from "M_Points" m where m.id < 10) as p
where st_dwithin(n.geom, p.geom, 0);

where 20000 is the radius (R) in projection units and geom is the geometry/geography column. You can replace it with a join or use a "with" clause instead of that long select st_buffer. Looks like you don't even need to Union those geometries. :) You can use ST_Within too:

ST_Within(n.geom, p.geom)