The CData JDBC Driver for Xero WorkflowMax supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT Clients.Name, ClientContacts.Name FROM Clients, ClientContacts WHERE Clients.Id=ClientContacts.ClientID

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT Clients.Name, ClientContacts.Name FROM Clients LEFT OUTER JOIN ClientContacts ON Clients.Id=ClientContacts.ClientID