The CData ADO.NET Provider for Odoo 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 res_users.name AS login, res_partner.name AS contact, res_partner.company_name AS company FROM res_users INNER JOIN res_partner ON res_users.partner_id = res_partner.id

Left Join

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

SELECT res_partner.name AS contact, res_users.login AS username FROM res_partner LEFT JOIN res_users ON res_partner.id = res_users.partner_id