ST_IsEmpty

定义

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

语法

sde.st_isempty (g1 sde.st_geometry)

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 ST_Geometry 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。

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)', 0)
);

INSERT INTO EMPTY_TEST VALUES (
'Point',
sde.st_pointfromtext ('point empty', 0)
);

INSERT INTO EMPTY_TEST VALUES (
'Linestring',
sde.st_linefromtext ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 0)
);

INSERT INTO EMPTY_TEST VALUES (
'Linestring',
sde.st_linefromtext ('linestring empty', 0)
);

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))', 0)
);

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)', 0)
);

INSERT INTO empty_test VALUES (
'Point',
sde.st_point ('point empty', 0)
);

INSERT INTO empty_test VALUES (
'Linestring',
sde.st_linestring ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 0)
);

INSERT INTO empty_test VALUES (
'Linestring',
sde.st_linestring ('linestring empty', 0)
);

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))', 0)
);

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

Oracle

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       1

PostgreSQL

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

3/7/2012