# 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

```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)```

ST_Geometry

## 示例

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)))', 0)
);

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 integer, shape sde.st_geometry);

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)))', 0)
);

SELECT 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))
``````
9/15/2013