SismemberCommand
SISMEMBER _key_ _member_
Time complexity O(1)Return 1 if member is a member of the set stored at key, otherwise0 is returned. On error a negative value is returned. Client librariesshould raise an error when a negative value is returned instead to passthe value to the caller.
Return value
Integer reply, specifically:1 if the element is a member of the set 0 if the element is not a member of the set OR if the key does not exist -2 if the key does not hold a set value