How to query objects within 1000m epsg4326?

Question

I have a PostGIS table having a column "geom" having a type geometry(MultiPolygon) and the projection epsg:4326 (degree decimal), I want to query all objects within 1000m and I use this query:

SELECT ST_AsGeoJSON(geom) FROM table 
WHERE ST_DWithin(geom, 'POINT(long lat)', 1000.0);

but I always ended up querying all objects.

Answer 1

Cast your geometries to GEOGRAPHY type:

SELECT ST_AsGeoJSON(geom) FROM table WHERE ST_DWithin(geom::geography, ST_GeographyFromText('POINT(long lat)'), 1000.0);

otherwise, PostGIS will treat the value "1000" as 1000 decimal degrees, which effectively means "return all objects".

Answer 2

For a multipolygon column, this works for me:

SELECT
    ST_AsGeoJSON(geom) 
FROM table 
   WHERE ST_Intersects(ST_Buffer(geom, 1000), 'SRID=4326;POINT(long lat)'::geometry);

EDIT

Michal is right with the buffer. I tried it without using the geography type and this seems to work as well.

SELECT
    ST_AsGeoJSON(geom)
FROM table 
    WHERE ST_DWithin(geom, 'SRID=4326;POINT(long lat)'::geometry, 1000);