ST_CollectionExtract — Given a GEOMETRYCOLLECTION, returns a MULTI* geometry consisting only of the specified type. Sub-geometries that are not the specified type are ignored. If there are no sub-geometries of the right type, an EMPTY collection will be returned. Only points, lines and polygons are supported. Type numbers are 1 == POINT, 2 == LINESTRING, 3 == POLYGON.
geometry ST_CollectionExtract(geometry collection, integer type);
Given a GEOMETRYCOLLECTION, returns a MULTI* geometry consisting only of the specified type. Sub-geometries that are not the specified type are ignored. If there are no sub-geometries of the right type, an EMPTY collection will be returned. Only points, lines and polygons are supported. Type numbers are 1 == POINT, 2 == LINESTRING, 3 == POLYGON.
Availability: 1.5.0
-- Constants: 1 == POINT, 2 == LINESTRING, 3 == POLYGON
SELECT ST_AsText(ST_CollectionExtract(ST_GeomFromText('GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(POINT(0 0)))'),1));
st_astext
---------------
MULTIPOINT(0 0)
(1 row)
SELECT ST_AsText(ST_CollectionExtract(ST_GeomFromText('GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(LINESTRING(0 0, 1 1)),LINESTRING(2 2, 3 3))'),2));
st_astext
---------------
MULTILINESTRING((0 0, 1 1), (2 2, 3 3))
(1 row)