SunionCommand
Time complexity O(N) where N is the total number of elements in all the provided setsReturn the members of a set resulting from the union of all thesets hold at the specified keys. Like in LRANGE the result is sent tothe client as a multi-bulk reply (see the protocol specification formore information). If just a single key is specified, then this commandproduces the same result as SELEMENTS.
Non existing keys are considered like empty sets.
Multi bulk reply, specifically the list of common elements.
