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12.16.7.5 GeometryCollection Property Functions

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These functions return properties of GeometryCollection values.

Unless otherwise specified, functions in this section handle their arguments as follows:

  • If any argument is NULL or any geometry argument is an empty geometry, the return value is NULL.

  • If any geometry argument is not a syntactically well-formed geometry, an ER_GIS_INVALID_DATA error occurs.

  • If any geometry argument has an SRID value that refers to an undefined spatial reference system (SRS), an ER_SRS_NOT_FOUND error occurs.

  • Otherwise, the return value is non-NULL.

These functions are available for obtaining geometry collection properties:

  • ST_GeometryN(gc, N)

    Returns the N-th geometry in the GeometryCollection value gc. Geometries are numbered beginning with 1.

    ST_GeometryN() handles its arguments as described in the introduction to this section.

    1. mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';
    2. mysql> SELECT ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1));
    3. +-------------------------------------------------+
    4. | ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)) |
    5. +-------------------------------------------------+
    6. | POINT(1 1)                                      |
    7. +-------------------------------------------------+

  • ST_NumGeometries(gc)

    Returns the number of geometries in the GeometryCollection value gc.

    ST_NumGeometries() handles its arguments as described in the introduction to this section.

    1. mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';
    2. mysql> SELECT ST_NumGeometries(ST_GeomFromText(@gc));
    3. +----------------------------------------+
    4. | ST_NumGeometries(ST_GeomFromText(@gc)) |
    5. +----------------------------------------+
    6. |                                      2 |
    7. +----------------------------------------+

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Document created the 26/06/2006, last modified the 26/10/2018
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