HEXISTS key field
This is a predicate to check whether or not the given
field exists in the hash that is specified by the given
fieldexist, 1 is returned.
fielddoes not exist, 0 is returned.
keyis associated with non-hash data, an error is raised.
Returns existence status as integer, either 1 or 0.
$ HSET yugahash area1 "America"
$ HEXISTS yugahash area1
$ HEXISTS yugahash area_none