Définition
ST_Union renvoie un objet géométrie qui représente la combinaison de deux objets source.
Syntaxe
Oracle et PostgreSQL
sde.st_union (geometry1 sde.st_geometry, geometry2 sde.st_geometry)
SQLite
st_union (geometry1 geometryblob, geometry2 geometryblob)
Type de retour
Oracle et PostgreSQL
ST_Geometry
SQLite
Geometryblob
Exemple
La table sensitive_areas stocke les ID des institutions menacées en plus de la colonne shape qui stocke les géométries de type polygone des institutions.
La table hazardous_sites stocke l'identité des sites dans la colonne id, tandis que l'emplacement géographique réel de chaque site est stocké dans la colonne des points de site.
La fonction ST_Buffer génère une zone tampon qui entoure les sites de dépôt de déchets dangereux. La fonction ST_Union génère des polygones à partir de l'union des polygones des sites de dépôt de déchets dangereux placés dans la zone tampon et des zones sensibles. La fonction ST_Area retourne la superficie de ces polygones.
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