ZUNION
Syntax
        ZUNION numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE <SUM | MIN | MAX>] [WITHSCORES]
- Available since:
 - 6.2.0
 - Time complexity:
 - O(N)+O(M*log(M)) with N being the sum of the sizes of the input sorted sets, and M being the number of elements in the resulting sorted set.
 - ACL categories:
 - 
              
                
@read,@sortedset,@slow, 
This command is similar to ZUNIONSTORE, but instead of storing the resulting
sorted set, it is returned to the client.
For a description of the WEIGHTS and AGGREGATE options, see ZUNIONSTORE.