Definition
ST_Difference takes two geometry objects and returns a geometry object that is the difference of the source objects.
Syntax
Oracle and PostgreSQL
sde.st_difference (geometry1 sde.st_geometry, geometry2 sde.st_geometry)
SQLite
st_difference (geometry1 geometryblob, geometry2 geometryblob)
Return type
Oracle and PostgreSQL
ST_Geometry
SQLite
Geometryblob
Example
In the following examples, the city engineer needs to know the total area of the city's lot area not covered by buildings; therefore, she wants the sum of the lot area after the building area has been removed.
The city engineer equally joins the footprints and lots table on the lot_id and takes the sum of the area of the difference of the lots minus the footprints.
Oracle
--Create tables and insert values
CREATE TABLE footprints (
building_id integer,
footprint sde.st_geometry
);
CREATE TABLE lots (
lot_id integer,
lot sde.st_geometry
);
INSERT INTO footprints (building_id, footprint) VALUES (
1,
sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);
INSERT INTO footprints (building_id, footprint) VALUES (
2,
sde.st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);
INSERT INTO footprints (building_id, footprint) VALUES (
3,
sde.st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
1,
sde.st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
2,
sde.st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
3,
sde.st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);
SELECT SUM (sde.st_area (sde.st_difference (lot, footprint)))
FROM FOOTPRINTS bf, LOTS
WHERE bf.building_id = lots.lot_id;
SUM(ST_AREA(ST_DIFFERENCE(LOT,FOOTPRINT)))
114
PostgreSQL
--Create tables and insert values
CREATE TABLE footprints (
building_id integer,
footprint sde.st_geometry
);
CREATE TABLE lots (
lot_id integer,
lot sde.st_geometry
);
INSERT INTO footprints (building_id, footprint) VALUES (
1,
sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);
INSERT INTO footprints (building_id, footprint) VALUES (
2,
sde.st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);
INSERT INTO footprints (building_id, footprint) VALUES (
3,
sde.st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
1,
sde.st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
2,
sde.st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);
INSERT INTO lots (lot_id, lot) VALUES (
3,
sde.st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);
SELECT SUM (sde.st_area (sde.st_difference (lot, footprint)))
FROM footprints bf, lots
WHERE bf.building_id = lots.lot_id;
sum
114
SQLite
--Create tables, add geometry columns, and insert values
CREATE TABLE footprints (
building_id integer primary key autoincrement not null
);
SELECT AddGeometryColumn (
NULL,
'footprints',
'footprint',
4326,
'polygon',
'xy',
'null'
);
CREATE TABLE lots (
lot_id integer primary key autoincrement not null
);
SELECT AddGeometryColumn (
NULL,
'lots',
'lot',
4326,
'polygon',
'xy',
'null'
);
INSERT INTO footprints (footprint) VALUES (
st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);
INSERT INTO footprints (footprint) VALUES (
st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);
INSERT INTO footprints (footprint) VALUES (
st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);
INSERT INTO lots (lot) VALUES (
st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);
INSERT INTO lots (lot) VALUES (
st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);
INSERT INTO lots (lot) VALUES (
st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);
SELECT SUM (st_area (st_difference (lot, footprint)))
FROM footprints bf, lots
WHERE bf.building_id = lots.lot_id;
sum
114.0