The CData Cmdlets PowerShell Module for Amazon Marketplace 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 c.SellerOrderId, o.SellerSKU, o.NumberOfItems, o.QuantityShipped FROM Orders c INNER JOIN OrderItems o ON c.AmazonOrderId = o.AmazonOrderId

Left Join

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

 SELECT c.SellerOrderId, o.SellerSKU, o.NumberOfItems, o.QuantityShipped FROM Orders c LEFT JOIN OrderItems o ON c.AmazonOrderId = o.AmazonOrderId