oracle 计算本月数据之和与上月 之和的差值

Question

求教  一条sql，计算 两个月数据之和的 差值

Answer 1

sum(decode(to_char(日期,'yyyymm'),'201305',数据,0))-sum(decode(to_char(日期,'yyyymm'),'201304',数据,0))

Answer 2

select (select sum(decode(to_char(datadate,'mm'),'02',data,0)) from qiyedata)-(select sum(decode(to_char(datadate,'mm'),'01',data,0)) from qiyedata) from dual;