Support of UDF in expression

I have a user defined function AGG for generic aggregation used in underlying layer, use it in sql will be fine (select sales_date, AGG(sales_qty) as qty from SALE), howeve when I use it in expression (e.g. AGG([sales_qty])) I will get error: Unknown function AGG.

can I register my own list of UDF to eliminate this error? or just make it warning so use can bypass it if they want?

Thanks

Boris Yang

Where do you get the "Unknown function" error exactly?