A table SUBS_BILL_PYMT stores monthly bill payment information from subscribers. It always stores one month’s worth data.
Display subscriber IDs who paid bills more than once in a month on at least two different dates.
select SUBSCRIBER_ID, count(*) from SUBS_BILL_PYMT group by SUBSCRIBER_ID having count(*) > 1
This will print the occurence also in the result. If you dont want that count column then declare a view with above shown query and select SUBSCRIBER_ID from it.
I don't say this is the best answer for the question but this is what it came to my mind instantly.