Add the specified members to the set stored at key. Specified members that are already a member of this set are ignored. If key does not exist, a new set is created before adding the specified members.
An error is returned when the value stored at key is not a set.
Integer reply: the number of elements that were added to the set, not including all the elements already present into the set.
History>= 2.4: Accepts multiple member arguments. Redis versions before 2.4 are only able to add a single member per call.
redis> SADD myset "Hello"(integer) 1
redis> SADD myset "World"(integer) 1
redis> SADD myset "World"(integer) 0
redis> SMEMBERS myset1) "Hello" 2) "World" redis>