ST_IsEmpty

定义

如果 ST_Geometry 对象为空，则 ST_IsEmpty 返回 1（Oracle 和 SQLite）或 t (PostgreSQL)；否则返回 0（Oracle 和 SQLite）或 f (PostgreSQL)。

语法

Oracle 和 PostgreSQL

sde.st_isempty (geometry1 sde.st_geometry)

SQLite

st_isempty (geometry1 geometryblob)

返回类型

布尔型

示例

下面的 CREATE TABLE 语句将创建 empty_test 表，其中包含的 geotype 用于存储 g1 列中所存储的子类的数据类型。

此 INSERT 语句将向几何子类（点、线串和面）中插入两条记录：一条记录为空，另一条记录不为空。

此 SELECT 查询将返回 geotype 列中的几何类型和 ST_IsEmpty 函数的结果。

Oracle

CREATE TABLE empty_test (
 geotype varchar(20),
 g1 sde.st_geometry
);

INSERT INTO EMPTY_TEST VALUES (
 'Point',
 sde.st_pointfromtext ('point (10.02 20.01)', 4326)
);

INSERT INTO EMPTY_TEST VALUES (
 'Point',
 sde.st_pointfromtext ('point empty', 4326)
);

INSERT INTO EMPTY_TEST VALUES (
 'Linestring',
 sde.st_linefromtext ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);

INSERT INTO EMPTY_TEST VALUES (
 'Linestring',
 sde.st_linefromtext ('linestring empty', 4326)
);

INSERT INTO EMPTY_TEST VALUES (
 'Polygon',
 sde.st_polyfromtext ('polygon ((10.02 20.01, 11.92 35.64, 25.02 34.15,
19.15 33.94, 10.02 20.01))', 4326)
);

INSERT INTO EMPTY_TEST VALUES (
 'Polygon',
 sde.st_polyfromtext('polygon empty', 4326)
);

SELECT geotype, sde.st_isempty (g1) Is_it_empty
FROM EMPTY_TEST;

GEOTYPE    Is_it_empty

Point         0
Point         1
Linestring    0
Linestring    1
Polygon       0
Polygon       1

PostgreSQL

CREATE TABLE empty_test (
 geotype varchar(20),
 g1 sde.st_geometry
);

INSERT INTO empty_test VALUES (
 'Point',
 sde.st_point ('point (10.02 20.01)', 4326)
);

INSERT INTO empty_test VALUES (
 'Point',
 sde.st_point ('point empty', 4326)
);

INSERT INTO empty_test VALUES (
 'Linestring',
 sde.st_linestring ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);

INSERT INTO empty_test VALUES (
 'Linestring',
 sde.st_linestring ('linestring empty', 4326)
);

INSERT INTO empty_test VALUES (
 'Polygon',
 sde.st_polygon ('polygon ((10.02 20.01, 11.92 35.64, 25.02 34.15,
19.15 33.94, 10.02 20.01))', 4326)
);

INSERT INTO empty_test VALUES (
 'Polygon',
 sde.st_polygon ('polygon empty', 4326)
);

SELECT geotype, sde.st_isempty (g1)
 AS Is_it_empty
 FROM empty_test;

geotype   is_it_empty

Point         f
Point         t
Linestring    f
Linestring    t
Polygon       f
Polygon       f

SQLite

CREATE TABLE empty_test (
 geotype text(20)
);

SELECT AddGeometryColumn (
 NULL,
 'empty_test',
 'g1',
 4326,
 'geometry',
 'xy',
 'null'
);

INSERT INTO empty_test VALUES (
 'Point',
 st_point ('point (10.02 20.01)', 4326)
);

INSERT INTO empty_test VALUES (
 'Point',
 st_point ('point empty', 4326)
);

INSERT INTO empty_test VALUES (
 'Linestring',
 st_linestring ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);

INSERT INTO empty_test VALUES (
 'Linestring',
 st_linestring ('linestring empty', 4326)
);

INSERT INTO empty_test VALUES (
 'Polygon',
 st_polygon ('polygon ((10.02 20.01, 11.92 35.64, 25.02 34.15,
19.15 33.94, 10.02 20.01))', 4326)
);

INSERT INTO empty_test VALUES (
 'Polygon',
 st_polygon ('polygon empty', 4326)
);

SELECT geotype, st_isempty (g1)
 AS "Is_it_empty"
 FROM empty_test;

GEOTYPE    Is_it_empty

Point         0
Point         1
Linestring    0
Linestring    1
Polygon       0
Polygon       1