When you have a webservice query, and you want to select records from a module where a certain UI10 field is empty use:
Where 15 is the webservice ID for the module of the UI10 field (in this case salesorders). Then use the 'x', and add a 0.
'po_related_soid' is a placeholder for the fieldname you want to check on, replace that with your own. Of course also replace the module name with your own.
PHP Code:
select * from purchaseorder where po_related_soid = 15x0
Where 15 is the webservice ID for the module of the UI10 field (in this case salesorders). Then use the 'x', and add a 0.
'po_related_soid' is a placeholder for the fieldname you want to check on, replace that with your own. Of course also replace the module name with your own.