The CData ADO.NET Provider for Trello 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 b.BoardId, b.Name, p.PluginId FROM Boards b INNER JOIN BoardPlugins p ON b.BoardId = p.BoardId

Left Join

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

SELECT b.BoardId, b.Name, p.PluginId FROM Boards b LEFT  JOIN BoardPlugins p ON b.BoardId = p.BoardId