postgis - Adding a GIS feature to existing database entry with QGIS

I've built a database with postgreSQL with tables, which include geometry columns. When I add some data to my non-geometry columns, I can see them in QGIS when I connect to my database using postgis. Now, I want to add polygons to the existing entries with the editing tool in QGIS. That means, filling up the geometry columns in QGIS.

How can I do this? I've only heard about adding whole shapefiles to the database but not to add single features to a single column.

An example... I have the following table (municipality):

id smallint NOT NULL,

name varchar(50) NOT NULL,
mun_geom geometry(Polygon, 31468)

I can fill the columns id and name in postgresql when I'm connected to my database (like (1,'municipality1')). After adding municipality as a postgis layer I want to complement the entry with adding a polygon feature.

Answer

I tried to do something similar to what you're doing in Spatialite, I had a table and wanted to add and populate a geometry column for that table. I wasn't able to do it directly, but what I ended up with worked. I added a second table with just two fields, a key to match back to my original table and my geometry column. I populated it then created a view that combined the two tables. You can do the same, or you can populate the second table then use an UPDATE query to fill in the geometry column of your first table if you want everything in just one table.