The Salesforce Marketing Cloud Adapter 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 ListSend.NumberSent, Send.Id FROM ListSend, Send WHERE ListSend.SendId=Send.Id

Left Join

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

SELECT ListSend.NumberSent, Send.Id FROM ListSend LEFT OUTER JOIN SendId ON ListSend.SendId=Send.Id