ApsaraDB RDS:ST_Dump

Syntax

geometry_dump[] ST_Dump(geometry g1);

Parameters

Description

ST_Dump extracts the components of a geometry object. Each returned geometry_dump record contains two fields:

• geom: the component geometry object

• path: an integer array indicating the position of the component within the original geometry

Behavior varies by input type:

• Point, LineString, or polygon input — Returns a single record with an empty path array and the input geometry as geom.

• Multi-geometry or collection input — Returns one record per component, with a path array indicating each component's position within the collection.

ST_Dump is the inverse of GROUP BY: where GROUP BY aggregates rows into a single geometry, ST_Dump expands a single geometry into multiple rows. A typical use case is expanding a MultiPolygon into individual polygons.

The function supports the following geometry types: Circular String, curve, Polyhedral Surface, Triangle, triangulated irregular network (TIN) surfaces, and 3D objects.

Examples

The following example expands a MULTILINESTRING into its component LINESTRING geometries. The path column shows the position of each component.

SELECT (t.dump).path, ST_AsText((t.dump).geom)
FROM (
  SELECT ST_Dump('MULTILINESTRING((0 0,0 2),(0 1,0 3))'::geometry) AS dump
) AS t;

Output:

 path |      st_astext
------+---------------------
 {1}  | LINESTRING(0 0,0 2)
 {2}  | LINESTRING(0 1,0 3)
(2 rows)