No problem, I'm glad you posted the solution, it may be very helpful to others facing the same problem.

>>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.