This is simpler than what gp is asking for, they want the ability to dynamically change which columns are requested too, so change it to "foo, bar, baz", but still do so with reasonable safety.
fmt ("SELECT {:v}, {:v} FROM {:v} WHERE id = {}", colname1, colname2, tablename, id);
The :v means "don't quote this, insert this string exactly as specified." It also has specialized handling for NULL values (i.e. it can generate 'IS NULL' instead of '= ...' if the value passed on is intended as a NULL value).
