As Bborie points out it is quite simple. But I can image that if you are not that experienced you would like to have an example. I know I do!
The trick is that the polygons with which you erase have to be union together.
DROP TABLE IF EXISTS blade_polygon_union;
CREATE TABLE blade_polygon_union AS
SELECT ST_Union(geom) as geom
Now we can use them to erase from the polygons
DROP TABLE IF EXISTS polygons_erased;
CREATE TABLE polygons_erased AS
SELECT ST_Difference(a.geom, b.geom) as geom, *
FROM blade_polygon_union as b, polygons as a
WHERE a.geom && b.geom;
And the result:
Hope this helps, sadly this is not the quickest of procedures, especially on large areas. If someone has a quicker solution in which the union is not required I’d be happy to hear it.