Aggregates a complex geometry object into a new geometry object-ApsaraDB RDS(RDS)-阿里云帮助中心

This topic describes the ST_UnaryUnion function. This function aggregates a complex geometry object and returns a new geometry object.

Syntax

geometry ST_UnaryUnion(geometry geom, float8 gridsize default -1.0, cstring options default '{}'); 
geometry ST_UnaryUnion(geometry geom , cstring options);

Parameters

Parameter Name	Description
geom	The Geometry object. This is typically a complex Geometry, MultiGeometry, or GeometryCollection.
gridsize	The grid size. Vertices in the same grid are merged during the union operation. The default value is -1.0, which disables this parameter.
options	Use this parameter to enable parallel execution and specify the degree of parallelism. The degree of parallelism ranges from 1 to 64. The value must be a JSON string. For example, `'{"parallel": 4}'` enables parallel computing and sets the degree of parallelism to 4. The default value is `'{}'`, which specifies sequential execution.

Examples

select st_area(st_union(geom)) from tableA where id = 1;
select st_area(st_union(geom, 0.005)) from tableA where id = 1;
select st_area(st_union(geom, '{"parallel": 4}'::cstring)) from tableA where id = 1;