PolarDB:ST_Dump

Syntax

geometry_dump[] ST_Dump(geometry g1);

Parameters

Description

ST_Dump extracts the components of a geometry and returns one geometry_dump row per component. Each row contains two fields:

• geom — the component geometry

• path — an integer array indicating the position of the component within the input geometry

The behavior depends on the geometry type of the input:

• Point, LineString, or Polygon — returns a single row with an empty path array and the original geometry as geom.

• Multi* geometry or GeometryCollection — returns one row per component, with path indicating each component's position in the collection.

ST_Dump is the inverse of GROUP BY: where that operation combines rows into a single geometry, ST_Dump expands a single geometry into multiple rows. A common use case is expanding a MultiPolygon into individual Polygon geometries.

Supported geometry types:

• Circular strings and curves

• Polyhedral surfaces

• Triangles and triangulated irregular network (TIN) surfaces

• 3D geometries

Examples

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;

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