Turning a single MultiPolygon into many small polygons?

As OP figured out, the ST_Dump function from PostGIS is one way to explode multipart geometries to single ones:

When the input geometry is a collection or multi it will return a record for each of the collection components, ... .

ST_Dump is useful for expanding geometries. ... . For example it can be use to expand MULTIPOLYGONS into POLYGONS.

SELECT sometable.field1, 
       (ST_Dump(sometable.the_geom)).geom AS the_geom
FROM sometable;

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The following is a related post with Python alternatives: Converting huge multipolygon to polygons