In SAP Public Cloud I want to create a custom CDS but I cannot aggregate values

[CarlosMoreira]

In SAP Public Cloud I've created a Custom Standard CDS where I only have 4 fields:
Purchase Order, Purchase Order Item, Quantity Unit and Quantity. In the Elements Properties tab, I have defined the quantity field as an aggregation by Sum. 

When I do Data Browser to check the data, the quantity is not aggregated (The Unit is the same for all PO that I am checking). I am assuming that the Group By is automatically set to all the available fields in the CDS.
What am I missing?

Thanks

[OwenLiu]

We helped you to accept the answer as solution. You can un-accept it anytime if you have further questions.

[Aukasz_SaBek · Accepted solution]

Please check this topic : https://community.sap.com/t5/enterprise-resource-planning-q-a/cds-do-not-aggregate-quantities/qaq-p/...

Please also check SAP HELP : https://help.sap.com/doc/abapdocu_740_index_htm/7.40/en-US/index.htm?file=abencds.htm