Joining between different data sources are possible in global data jobs, e.g.
select *
from <%=DATASOURCE:MDT_100%>.EKPO A
join <%=DATASOURCE:MDT_200%>.EKPO B ON ...
But is it possible to join each other within the scoped data jobs (MDT_100, MDT_200), that means
Scope MDT_100:
select *
from EKPO A
join <%=DATASOURCE:MDT_200%>.EKPO B ON ...