data _null_;
set ex1;
if ORIGIN_COUNTRY="OTHER" then call symput('other',ORIGIN_LOAD);
run;
proc sql;
create table c as
select b.*,(case when a.ORIGIN_LOAD is null then &other else a.ORIGIN_LOAD end ) as ORIGIN_LOAD
from ex2 b left join ex1 a on a.ORIGIN_COUNTRY=b.Country;
quit;