Hi Rubane,
I don't have EPM installed here but based on this Table User Defined Functions( Table UDF ) in HANA you are not properly defining the source table.
In your case missing 1) schema of EPM, 2) not using double quotes, 3) separation of package and view, 4) missing camel case on purchaseOrderItem:
FROM sap.hana.democontent.epm.data.products AS P , sap.hana.democontent.epm.data.purchaseorderitem AS B
On blog:
from "SAP_HANA_EPM_DEMO"."sap.hana.democontent.epm.data::businessPartner" as a
SAP_HANA_EPM_DEMO is the schema
sap.hana.democontent.epm.data is the package
businessPartner is the view
Start simple... before the seletion try it out on Studio SQL.
Regards, Fernando Da Rós