The CData Excel Add-In for Jira Service Management 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 c.RequestTypeId, o.Name FROM Requests c INNER JOIN RequestsParticipants o ON c.RequestId = o.RequestId 

Left Join

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

 SELECT c.RequestTypeId, o.Name FROM Requests c LEFT JOIN RequestsParticipants o ON c.RequestId = o.RequestId