Fixing polygon with ring self-intersection in QGIS

Question

When I polygonize a raster, I very often have 'pixels' holes/interior ring that touches exterior ring.

An example:

POLYGON((5 0, 10 0, 10 10, 0 10, 0 0, 5 0, 3 3, 5 6, 7 3, 5 0))

It's defined as an invalid geometry in the OGC geometry specifications.

In QGIS, how to fix this?

Answer 1

I've found the solution here but for PostGIS: https://gis.stackexchange.com/a/15301/93097 and I've test it in Spatialite/Virtual layers, and it works.

Bellow the code I use with a shapefile 'my_layer' with one field "DN":

SELECT DN, ST_Buffer(geometry, 0.0) as geometry
FROM my_layer;