The CData ADO.NET Provider for Reckon 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.ReferenceNumber, c.AccountNumber FROM Invoices i INNER JOIN Customers c ON i.CustomerId=c.ID

Left Join

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

SELECT i.ReferenceNumber, c.AccountNumber FROM Invoices i LEFT JOIN Customers c ON i.CustomerId=c.ID