The CData Cmdlets PowerShell Module 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]