Purchase Order Authorisation Question

Hi,

Just after some assistance on creating a SQL purchase order authorisation.

I would like to set an authorisation where SAP will check that there is a BASEREF (Sales Order) for the purchase order line item being created.

We would like to stop any purchase orders being created where there is no related sales order..

I have the following pseudo code

select 'True' 
from POR1 P
WHERE P.ITEMCODE=$[$38.1.0] AND P.BaseRef IS NULL OR P.BaseRef =''

any help would be great

Brendan