now I want to set superkey on (VENDORID+ADDRESS+CITY) which identify unique record.
Why three of them? Are you saying that VENDORID in your VENDOR table is not unique by itself?
Or, you want to say that the same Vendor can have different addresses or at the same address you may hold multiple vendors? If so, you better create separate Address and VendorAddress tables to this data in RDBMS way. Address table will have AddressId and address details and VendorAddress will have VendorId and AddressId as a composite PK?
Or, at least, just have separate VendorAddress table to store multiple vendor addresses in your way. Still, it will be way better than storing multiple records of the same vendor in Vendor table...
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