Search Points within Buffered Polygon with PostGIS

Question

I have a table of boundaries as polygons and another table of peaks as points. I want to find the points that are within the polygons and the polygons are extended with a buffer. What would be the fastest way to do that?

At the moment I am trying to work with ST_Within which gives me good results, but adding ST_Buffer does not seem to work:

SELECT p.name, p.elev, a.name FROM eu_peaks p, eu_admin_valid a where
    ST_Within(p.geom, ST_Buffer(a.the_geom, 0.02))
    order by a.name;

Is this a good approach? What should I change?

Answer 1

Buffering is an expensive process. The preferred method is st_DWithin. Your query could be:

SELECT
  p.name, p.elev, a.name
FROM
  eu_peaks p, eu_admin_valid a
WHERE
  ST_DWithin(p.geom, a.the_geom, 0.02)
ORDER BY
  a.name;