[Qgis-user] Add circular string tool

[Piotr Kania]

Hi!

Sorry if my question is "stupid" - I am learning all the time.

In postgis database I have two tables - let's say 'polygons' (gid, 
the_geom,MultiPolygon,srid=2180) and 'lines' (gid, 
the_geom,MultLineString,srid=2180). I'd like to use "Add circular string 
tool" from qgis to create same arcs and save in those layers. From web 
and from qgis error message (Geometry type (MultiSurface) does not match 
column type (MultiPolygon); Geometry type (MultiCurve) does not match 
column type (MultiLineString)
I know that I should have tables in postgis with geometry type 
MultiSurface and MultiCurve.

Here is my question: how should I do that? Can I have that kind of 
geometry type added respectively to my existing tables ie. MultiSurface 
to 'polygons' and MultiCurve to 'lines'? If anyone can give working 
solutions in sql code? Thanks