Converting from MultiPolygon to Polygon in PostGIS

Question

I have a table in PostGIS, where the data is currently stored as a MultiPolygon. Each Multipolygon has only a single Polygon in it.

How do I query and get the containing Polygon, and not MultiPolygon? I am ok ignoring the Edge case where there are Multiple Polygons in the Multi-Polygon Geometry. All I need is the first or only Polygon in that Geometry.

Answer 1

If you want to Ignore the edge cases, and get only the First (or only) Polygon, from the MultiPolygon geometry, then you need to use the ST_GeometryN() function.

A query like the following will give you the geometry as Polygons

SELECT ST_GeometryN(geom, 1)
FROM polygons;