PostGIS: why does it return an error when changing geometry to GeometryCollection?

Question

I've got a postgreSQL/postGIS table whose geom column holds Geometry type (MultiLineString). I want to include in the table also Points and MultiPoints, so I tried to change the geometry type with

alter table lineas
alter column geom type geometry(geometrycollection);

However, it returns

ERROR:  Geometry type (MultiLineString) does not match column type (GeometryCollection)
SQL state: 22023

Why is that? A GeometryCollection column shoud be able to admit all other types, shouldn't it? How can it be solved?

Answer 1

A GeometryCollection can aggregate any kind of geometries but it is still a specific type of geometry.

If you want a column that can contain any kind of geometry, use the base type Geometry.

4.3.2. The GEOMETRY_COLUMNS VIEW of https://postgis.net/docs/using_postgis_dbmanagement.html says

To restrict the spatial column to a single type, use one of: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION or corresponding XYM versions POINTM, LINESTRINGM, POLYGONM, MULTIPOINTM, MULTILINESTRINGM, MULTIPOLYGONM, GEOMETRYCOLLECTIONM. For heterogeneous (mixed-type) collections, you can use "GEOMETRY" as the type.