I think it is not set to some property instead stored in some nested property. You can try to create the grid dynamically that would create the column based on the report defination. Or you can source the grid from activity and the call the RD from the activity and then loop through the results and store the SQl generated value to somewhere else.
Thank you Saikat for your reply.Yes SQl function return value save to the the OOTB property and as per my workaround we cannot we refer it directly. We can refer it via the section and but again i am unable to filter it.