Try:
Select case when tblincome.date is null and tblexpense.date is not null then tblexpense.date
when tblincome.date is not null and tblexpense.date is null then tblincome.date
when tblincome.date is not null and tblexpense.date is not null then tblincome.date
end as Date,
Sum(tblincome.income), Sum(tblexpense.expense) from tblincome full join tblexpense
ON tblincome.date = tblexpense.date
where tblincome.date between '2014-01-01' AND '2014-02-01'