Is there a way to display more results than there are rows?

If I have a table customer with 20 rows, is there a way to get more 20 rows, "faking" the additional ones?

Maybe an outer join on itself, using a field of the same type but with different values so you will not have a match?

This would come in very handy for test data.

If not possible with only 1 table, would a related table (whose data is irrelevant and would only be used to assist in faking rows) help?

If it is not possible in T-SQL, do you know if it is possible in other SQL dialects?

Thanks!