定义
ST_Difference 获取两个几何对象,然后返回表示两个源对象之差的几何对象。
语法
Oracle 和 PostgreSQL
sde.st_difference (geometry1 sde.st_geometry, geometry2 sde.st_geometry)
SQLite
st_difference (geometry1 geometryblob, geometry2 geometryblob)
返回类型
Oracle 和 PostgreSQL
ST_Geometry
SQLite
Geometryblob
示例
在下面的示例中,城市工程师需要知道未被建筑物覆盖的城市地块的总面积;因此,她想要知道减去建筑物面积之后的地块面积的总和。
城市工程师通过 lot_id 相等连接 footprints 表和 lots 表,然后获取地块减去覆盖区之后的差值面积之和。
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