The CData JDBC Driver for GraphQL supports standard SQL joins like the following examples.
An inner join selects only rows from both tables that match the join condition:
SELECT Commits.AuthorName, CommitComments.Body FROM Commits, CommitComments WHERE Commits.Sha=CommitComments.CommitSha
A left join selects all rows in the FROM table and only matching rows in the JOIN table:
SELECT Commits.AuthorName, CommitComments.Body FROM Commits LEFT OUTER JOIN CommitComments ON Commits.Sha=CommitComments.CommitSha