The CData ADO.NET Provider for Acumatica 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 Customer.CustomerName, MainContact.DisplayName FROM Customer, Customer_Maincontact WHERE Customer.CustomerID=Customer_Maincontact.ParentCustomerID

Left Join

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

SELECT Groups.displayName, Conversations.Topic FROM Groups LEFT OUTER JOIN Conversations ON Groups.Id=Conversations.GroupId