The CData Excel Add-In for Exact Online 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 Accounts.Name, Contacts.FullName FROM Accounts, Contacts WHERE Accounts.ID=Contacts.Account

Left Join

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

SELECT Accounts.Name, Contacts.FullName FROM Accounts LEFT OUTER JOIN Contacts ON Accounts.ID=Contacts.Account