avg() from multiple columns

I have a question regarding taking the average value from several
columns.

I am trying to evaluate a survey with sql. I have one column per
question, and one row per answered survey. The answers can have values 1

- 4, unanswered questions have 0. I want to take the average from the
answers of several questions that belong to the same category. For one
question I can do like this:

igv=> select avg("1.2") from igvdata
igv-> where "1.2" > 0;

How do I go about to have averages for several columns? Do I have to
create views in order to avoid the "no answer"-values for each column?

Thanks in advance,

Miia