ST_GeometryN

定义

ST_GeometryN 获取一个集合和一个整数索引，然后返回集合中的第 n 个 ST_Geometry 对象。

语法

Oracle 和 PostgreSQL

sde.st_geometryn (mpt1 sde.st_multipoint, index integer)
sde.st_geometryn (mln1 sde.st_multilinestring, index integer)
sde.st_geometryn (mpl1 sde.st_multipolygon, index integer)

SQLite

st_geometryn (mpt1 st_multipoint, index integer)
st_geometryn (mln1 st_multilinestring, index integer)
st_geometryn (mpl1 st_multipolygon, index integer) 

返回类型

Oracle 和 PostgreSQL

ST_Geometry

SQLite

Geometryblob

示例

在本示例中，将创建一个多面。然后使用 ST_GeometryN 列出多面的第二个元素。

Oracle

CREATE TABLE districts (
 dist_id integer,
 shape sde.st_multipolygon
);

INSERT INTO DISTRICTS (dist_id, shape) VALUES (
 1,
 sde.st_multipolygon ('multipolygon (((-1 -1, -1 11, 11 11, 11 -1, -1 -1),
(19 -1, 19 11, 29 9, 31 -1, 19 -1), (39 -1, 39 11, 51 11, 51 -1, 39 -1)))', 4326)
);

SELECT sde.st_astext (sde.st_geometryn (shape, 2)) Second_Element
 FROM DISTRICTS;

Second_Element

POLYGON  ((-1.00000000 -1.00000000, 11.00000000 -1.00000000, 11.0000000 0 11.000

PostgreSQL

CREATE TABLE districts (
 dist_id serial,
 shape sde.st_geometry
);

INSERT INTO districts (shape) VALUES (
 sde.st_multipolygon ('multipolygon (((-1 -1, -1 11, 11 11, 11 -1, -1 -1),
(19 -1, 19 11, 29 9, 31 -1, 19 -1), (39 -1, 39 11, 51 11, 51 -1, 39 -1)))', 4326)
);

SELECT sde.st_astext (sde.st_geometryn (shape, 2)) AS Second_Element
 FROM districts;

second_element

POLYGON  ((39 -1, 51 -1, 51 11, 39 11, 39 -1))

SQLite

CREATE TABLE districts (
 dist_id integer primary key autoincrement not null
);

SELECT AddGeometryColumn (
 NULL,
 'districts',
 'shape',
 4326,
 'multipolygon',
 'xy',
 'null'
);

INSERT INTO districts (shape) VALUES (
 st_multipolygon ('multipolygon (((-1 -1, -1 11, 11 11, 11 -1, -1 -1),
(19 -1, 19 11, 29 9, 31 -1, 19 -1), (39 -1, 39 11, 51 11, 51 -1, 39 -1)))', 4326)
);

SELECT st_astext (st_geometryn (shape, 2))
 AS "Second_Element"
 FROM districts;

Second_Element

POLYGON  ((39.00000000 -1.00000000, 51.00000000 -1.00000000, 51.00000000 11.00000000, 39.00000000 11.00000000, 39.00000000 -1.00000000))