SQL select statement that shows non-existant column?

Question

If I have a application that accepts a query that returns 4 columns, 1 of which is an extra info column that can be empty, and the column doesn't exist in the database I am using how could I 'create' it so that the data retrieved using the query always has 4 columns, 1 nbeing empty?

Answer 1

select c1, c2, c3, null as c4 from table;

Answer 2

This would work in Oracle, haven't tried in anything else:

select null thiscolumnisempty, id,id2,id3 from table