Result of DataService Comparing to the RDB

I have studied Data Service and i like to confirm my understanding here.
The provided example resource about “Olympic”, i assume DataService can only perform only inner join is it true?
There are Olympics and Nations Entity, they have relationship. Related records can get by Query Entity Records. In the “Query Entity Records” is has equal to,not equal to , and group by.
But there is no Outer join , left join and right join comparing to the RDB.
Thank you for your time.
Best regards

HI @eimon - Yes, you are right that Data Service doesn’t support SQL like constructs of outer join, left join or right join because the Query activity doesn’t really support joining. The query activity allows you to query records based on existing relationship set-up between the entities.

Using the query activity allows you to query records like saying, give me all Medals for Olympics 2016 or say give me Medals where Olympics is not 2016.

Thinking about it like SQL ‘join’ construct will not work. Think of Data Service as having relationship (1 to Many at record level) and filtering of data from entities or related entities.