sap hana calculated column check for multiple IDs - if-statement

Question

i want to create a calculated column, which will show two values: Y or N
2 columns are here important, "VAT-ID" and "CUSTOMER-ID". the calculated column will check if a customer-ID has multiple VAT-IDs. If yes the value "Y" should be displayed, else "N".
for example, the first 5 rows of the customer-id column are:
123456
654321
666666
123456
654321
the first 5 rows of the VAT-id column are:
EE999999999
AA999999999
GG999999999
KK999999999
AA999999999
the first 5 rows of the calculated column should be then:
Y
N
N
Y
N
any Help would be appreciated

Answer 1

Calculated columns don’t allow for aggregations across groups or other than the current row.
What you can do to achieve your goal is to create a separate aggregation node and count distinct VAT-IDs grouped by CUSTOMER-ID.
With this, you can now have a calculated column that checks for VAT-ID-COUNT > 1 and map it to your Y/N values.

Answer 2

As Lars mentioned it is not possible to use a window function within a calculated field on HANA table
But you can use following query to check if VAT number is multiple for a customer or not
select
CustomerId, VATID,
case
when (count(*) over (partition by CustomerId, VATID)) > 1
then 'Y'
else 'N'
end
from CustomerVAT;