Multipart vs Single Part

Here's how some GIS databases treat multipart and single-part geometries.

Esri's various formats support multi- and single-part geometries stored in the same Polyline or Polygon feature class, though they do require separate feature classes for point and multipoint.

Without database tinkering, PostGIS stores only a single geometry type per column, so you can either store polygon or multipolygon but not both. Ditto for SpatiaLite.

MSSQLSpatial and Oracle Spatial support a generic geometry column where each instance can be any geometry type. Oracle Spatial also supports subclasses of the generic geometry type such as polygon and multipolygon, but not a generic "polygon" that includes both multi and single.