What kind of SQL operation has be applied to get from point A to point B :
I can't use DISTINCT , GROUPING prior to STRING_AGG operator , I don't see any other option how to reduce the number of 261, 262
You can very easily achieve this by using SPLIT_TO_TABLE hana function. Once you get the split values as rows in a one column table you can
SELECT DISTINCT them and then
STRING_AGG them as documented here
I'll let you put together the code to do this as I don't have a hana running environment to verify the correctness.
Hope it helped.