The CData Cmdlets PowerShell Module for Jira Assets 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 d.Id, f.ChildValue FROM Department d INNER JOIN Department_CF_ARelCol f ON d.Id = f.ParentId 

Left Join

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

 SELECT d.Id, f.ChildValue FROM Department d LEFT JOIN Department_CF_ARelCol f ON d.Id = f.ParentId