This command fetches all fields of the hash that is associated with the given
keydoes not exist, an empty list is returned.
keyis associated with non-hash data, an error is raised.
Returns list of fields in the specified hash.
$ HSET yugahash area1 "Africa"
$ HSET yugahash area2 "America"
$ HKEYS yugahash
1) "area1" 2) "area2"