ST_GeometryN
返回几何图形对象内的第 n 个几何图形。
如果 n 超出索引范围，则返回 NULL。
行为类型
不可变语法
ST_GeometryN( g , n )
参数
g- GEOMETRY 类型的空间对象。
n- 几何图形的索引号，从 1 开始。
返回
GEOMETRY
支持的数据类型
示例
以下示例显示了 ST_GeometryN 的用法。
返回多边形集合中的第二个几何图形：
=> CREATE TABLE multipolygon_geom (gid int, geom GEOMETRY(1000));
CREATE TABLE
=> COPY multipolygon_geom(gid, gx FILLER LONG VARCHAR, geom AS ST_GeomFromText(gx)) FROM stdin delimiter '|';
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>>9|MULTIPOLYGON(((2 6, 2 9, 6 9, 7 7, 4 6, 2 6)),((0 0, 0 5, 1 0, 0 0)),((0 2, 2 5, 4 5, 0 2)))
>>\.
=> SELECT gid, ST_AsText(ST_GeometryN(geom, 2)) FROM multipolygon_geom;
gid | ST_AsText
-----+--------------------------------
9 | POLYGON ((0 0, 0 5, 1 0, 0 0))
(1 row)
返回多边形集合内的所有几何图形：
=> CREATE TABLE multipolygon_geom (gid int, geom GEOMETRY(1000));
CREATE TABLE
=> COPY multipolygon_geom(gid, gx FILLER LONG VARCHAR, geom AS ST_GeomFromText(gx)) FROM stdin delimiter '|';
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>>9|MULTIPOLYGON(((2 6, 2 9, 6 9, 7 7, 4 6, 2 6)),((0 0, 0 5, 1 0, 0 0)),((0 2, 2 5, 4 5, 0 2)))
>>\.
=> CREATE TABLE series_numbers (numbs int);
CREATE TABLE
=> COPY series_numbers FROM STDIN;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 1
>> 2
>> 3
>> 4
>> 5
>> \.
=> SELECT numbs, ST_AsText(ST_GeometryN(geom, numbs))
FROM multipolygon_geom, series_numbers
WHERE ST_AsText(ST_GeometryN(geom, numbs)) IS NOT NULL
ORDER BY numbs ASC;
numbs | ST_AsText
-------+------------------------------------------
1 | POLYGON ((2 6, 2 9, 6 9, 7 7, 4 6, 2 6))
2 | POLYGON ((0 0, 0 5, 1 0, 0 0))
3 | POLYGON ((0 2, 2 5, 4 5, 0 2))
(3 rows)