Custom expression from two tables

Hello,

I get it to work with multiple fields in the dropdown list.

How can I get values from another table too?
Ex

Table Personal

. id

. name

. age

. country (int) -> Countrylist
Table Countrylist

. id

. country
I will have a dropdown list showing "name country". If I only print:

concat(name,' ',country)

it will show, ex "Pelle 46" (If the name is Pelle and country 46 in the country (pointing on Country list id 46).

I will have "Pelle Sweden" instead. How can I do that?
/Pelle