ST_Union

Definition

ST_Union returns a geometry object that is the combination of two source objects.

Syntax

Oracle and PostgreSQL

sde.st_union (geometry1 sde.st_geometry, geometry2 sde.st_geometry)

SQLite

st_union (geometry1 geometryblob, geometry2 geometryblob)

Return type

Oracle and PostgreSQL

ST_Geometry

SQLite

Geometryblob

Example

The sensitive_areas table stores the IDs of threatened institutions in addition to the shape column, which stores the institutions' polygon geometries.

The hazardous_sites table stores the identity of the sites in the id column, while the actual geographic location of each site is stored in the site point column.

The ST_Buffer function generates a buffer surrounding the hazardous waste sites. The ST_Union function generates polygons from the union of the buffered hazardous waste sites and sensitive area polygons. The ST_Area function returns the area of these polygons.

Oracle

CREATE TABLE sensitive_areas (
 id integer, 
 shape sde.st_geometry
); 

CREATE TABLE hazardous_sites (
 id integer, 
 site sde.st_geometry
);


INSERT INTO SENSITIVE_AREAS VALUES (
 1,
 sde.st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
 2,
 sde.st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
 3,
 sde.st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO HAZARDOUS_SITES VALUES (
 4,
 sde.st_geometry ('point (60 60)', 4326)
);

INSERT INTO HAZARDOUS_SITES VALUES (
 5,
 sde.st_geometry ('point (30 30)', 4326)
);

SELECT sa.id SA_ID, hs.id HS_ID,
 sde.st_area (sde.st_union (sde.st_buffer (hs.site, .01), sa.shape)) UNION_AREA
 FROM HAZARDOUS_SITES hs, SENSITIVE_AREAS sa;

     SA_ID  HS_ID     UNION_AREA

         1    4       100.000313935011
         2    4       400.000313935011
         3    4       400.000235451258
         1    5       100.000235451258
         2    5       400.000235451258
         3    5       400.000313935011

PostgreSQL

CREATE TABLE sensitive_areas (
 id integer, 
 shape sde.st_geometry
); 

CREATE TABLE hazardous_sites (
 id integer, 
 site sde.st_geometry
);


INSERT INTO SENSITIVE_AREAS VALUES (
 1,
 sde.st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
 2,
 sde.st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
 3,
 sde.st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO HAZARDOUS_SITES VALUES (
 4,
 sde.st_geometry ('point (60 60)', 4326)
);

INSERT INTO HAZARDOUS_SITES VALUES (
 5,
 sde.st_geometry ('point (30 30)', 4326)
);

SELECT sa.id AS SA_ID, hs.id AS HS_ID,
 sde.st_area (sde.st_union (sde.st_buffer (hs.site, .01), sa.shape)) AS UNION_AREA
 FROM hazardous_sites hs, sensitive_areas sa;

     sa_id  hs_id   union_area

         1    4       100.000313935011
         2    4       400.000313935011
         3    4       400.000235451258
         1    5       100.000235451258
         2    5       400.000235451258
         3    5       400.000313935011

SQLite

CREATE TABLE sensitive_areas (
 id integer
); 

SELECT AddGeometryColumn(
 NULL,
 'sensitive_areas',
 'shape',
 4326,
 'polygon',
 'xy',
 'null'
);

CREATE TABLE hazardous_sites (
 id integer
);

SELECT AddGeometryColumn(
 NULL,
 'hazardous_sites',
 'site',
 4326,
 'point',
 'xy',
 'null'
);

INSERT INTO sensitive_areas VALUES (
 10,
 st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO sensitive_areas VALUES (
 11,
 st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO sensitive_areas VALUES (
 12,
 st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO hazardous_sites VALUES (
 40,
 st_geometry ('point (60 60)', 4326)
);

INSERT INTO hazardous_sites VALUES (
 41,
 st_geometry ('point (30 30)', 4326)
);

SELECT sa.id AS "sa_id", hs.id AS "hs_id",
 st_area (st_union (st_buffer (hs.site, .01), sa.shape)) AS "union"
 FROM hazardous_sites hs, sensitive_areas sa;

     sa_id  hs_id   union

         1    4       100.000313935011
         2    4       400.000313935011
         3    4       400.000235451258
         1    5       100.000235451258
         2    5       400.000235451258
         3    5       400.000313935011