>Sorry, I have no experience with FireBird and this query looks quite complex to me.

My bad Naomi. It was more like FYI, the later part is complex yes but that is the way I code :) The actual recursive CTE portion is this, but like I said FYI:

WITH RECURSIVE Hier(iID, iPK) AS
   (SELECT p.iID, p.iID AS iPK FROM mItems p WHERE p.iID IN (SELECT ID
         FROM gttItemsSelected
         WHERE TRIM(JobID) = ?{vp_JobID})
   UNION ALL
   SELECT p2.iID, p2.iPID AS iPK FROM mItems p2
   JOIN Hier on p2.iPID = Hier.iID)
SELECT ...
      JOIN Hier
         ON sBOMIItem.iItemID = Hier.iID
...

Thanks.