I've read TikZ matrix as a replacement for tabular which nicely explained how to get table with borders in the first place.
Now, I'd like to have let's say thicker border (or double border line) between 2 & 3 columns of my multicolumn matrix. As far as I understand column sep is specified for entire matrix. So is it possible to mimic at least appearance of different border between some columns?
I want this to visually show on example how data was normalized in DB and I want to separate superkey from other columns.