有些情况获得的数据是Multi类型的，如MultiPolygon和MultiLineString类型，这些类型在空间计算上，很多函数都用不上。像如MultiLineString类型想进行最短路径查询就比较不方便。postgis导入的时候能够选择simple类型，但是有时候就是导不进去。
image.png
image.png
如上图这种情况，其实就可以将这些多边形进行打散，进行单独处理。这就需要用到st_numgeometries和st_geometryN两个函数了。
integer ST_NumGeometries(geometry geom);
Returns the number of Geometries. If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the number of geometries, for single geometries will return 1, otherwise return NULL.
SELECT ST_NumGeometries(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
st_numgeometries 计算Multi的单个数量
geometry ST_GeometryN(geometry geomA, integer n);
Return the 1-based Nth geometry if the geometry is a GEOMETRYCOLLECTION, (MULTI)POINT, (MULTI)LINESTRING, MULTICURVE or (MULTI)POLYGON, POLYHEDRALSURFACE Otherwise, return NULL
SELECT
n,
ST_AsEWKT (ST_GeometryN(the_geom, n)) AS geomewkt
FROM
(
VALUES
(
ST_GeomFromEWKT (
'MULTIPOINT(1 2 7, 3 4 7, 5 6 7, 8 9 10)'
)
),
(
ST_GeomFromEWKT (
'MULTICURVE(CIRCULARSTRING(2.5 2.5,4.5 2.5, 3.5 3.5), (10 11, 12 11))'
)
)
) AS foo (the_geom)
CROSS JOIN generate_series (1, 100) n
WHERE
n <= ST_NumGeometries (the_geom);
ST_GeometryN 取index为 n的geometry
SELECT st_geometryN(geom,n) from grid_class_sure_hex gcsh CROSS JOIN generate_series (1, 100) n where gcsh.name='aaaaa' and n <= ST_NumGeometries (gcsh.geom);
--其中generate_series (1, 100)可以根据情况自己设置
最后的每个小的多边形都可以点击，是能够达到效果的。
