Hi Blangero,
Aggregation has to specified explicitly. So for your first model of query, this query will work.
SELECT
sum( HSL)
FROM "_SYS_BIC"."tmp.fi.rtc.cube/ZRTC_C_ACDOCA0DL"
where rclnt = '500' and rldnr = '0L' and rcomp = 'ZFA2' and bilkt = '0003020000';
That's the reason it works in Excel when you try SELECT * - this fetches all the data and aggregation will be performed by Excel.
In the changed model, as the aggregation is pushed to the lowest level, HSL is aggregated and passed to next nodes. Hence SELECT HSL will work, as it is already aggregated.
Hope this clears your doubt, let us know if any questions.
Regards,
Chandra.