sap hana calculated column check for multiple IDs

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