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19.5.2.7. GeometryCollection函数

• GeometryN(gc,n)

  返回GeometryCollection值gc中第n个几何对象。几何对象的编号从1开始。

  mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';
  mysql> SELECT AsText(GeometryN(GeomFromText(@gc),1));
  +----------------------------------------+
  | AsText(GeometryN(GeomFromText(@gc),1)) |
  +----------------------------------------+
  | POINT(1 1)                             |
  +----------------------------------------+
  

• NumGeometries(gc)

  返回GeometryCollection值gc中几何对象的数目。

  mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';
  mysql> SELECT NumGeometries(GeomFromText(@gc));
  +----------------------------------+
  | NumGeometries(GeomFromText(@gc)) |
  +----------------------------------+
  |                                2 |
  +----------------------------------+