The CData FireDAC Components for Sage 300 supports standard SQL joins like the following examples.
An inner join selects only rows from both tables that match the join condition:
SELECT * FROM OEInvoices INNER JOIN OEInvoices_InvoiceDetails ON OEInvoices.InvoiceUniquifier=OEInvoices_InvoiceDetails.InvoiceUniquifier
A left join selects all rows in the FROM table and only matching rows in the JOIN table:
SELECT * FROM OEInvoices LEFT JOIN OEInvoices_InvoicePaymentSchedules ON OEInvoices.InvoiceUniquifier=OEInvoices_InvoicePaymentSchedules.InvoiceUniquifier