The CData ADO.NET Provider for Domino 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 p.firstname, c.color_choice FROM [Person] p INNER JOIN [color_choice] c ON c.[unid] = p.[unid]

Left Join

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

 SELECT p.firstname, c.color_choice FROM [Person] p LEFT JOIN [color_choice] c ON c.[unid] = p.[unid]