The CData Excel Add-In for QuickBooks 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 i.DocNumber, c.CompanyName FROM Invoices i INNER JOIN Customers c ON i.CustomerRef=c.Id

Left Join

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

SELECT i.DocNumber, c.CompanyName FROM Invoices i LEFT JOIN Customers c ON i.CustomerRef=c.Id