The CData ADO.NET Provider for Wave Financial 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 Invoices.Title, InvoiceItems.TotalValue FROM Invoices, InvoiceItems WHERE Invoices.Id=InvoiceItems.InvoiceId

Left Join

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

SELECT Invoices.Title, InvoiceItems.TotalValue FROM Invoices LEFT OUTER JOIN InvoiceItems ON Invoices.Id=InvoiceItems.InvoiceId