That if you had 2016 showed the difference between 2016 and 2017 also in the future will show years 2017 2018 2019 2020
I wanted this "DIF ANO" to be an expression without variable all leave the same table
Shipping Table: fields: Year, Origin, Destination, Value Freight.
This freight value is already = SUM (VALUE_FRETE) has many deliveries for those origin and destination and each origin and destination that I selected if it had delivery in two years showed that difference.