SaddCommand
SADD _key_ _member_
Time complexity O(1)Add the specified member to the set value stored at key. If memberis already a member of the set no operation is performed. If keydoes not exist a new set with the specified member as sole member iscrated. If the key exists but does not hold a set value an error isreturned.
Return value
Integer reply, specifically:1 if the new element was added 0 if the new element was already a member of the set -2 if the key contains a non set value