Available since: 1.0.0
Time complexity: O(1) for each element added, so O(N) to add N elements when the command is called with multiple arguments.
Add the specified members to the set stored at
Specified members that are already a member of this set are ignored.
key does not exist, a new set is created before adding the specified
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 in the set.