 Usage:

ZDIFF numkeys key [ key ... ] [ withscores ]
 Complexity:
 O(L + (NK)log(N)) worst case where L is the total number of elements in all the sets, N is the size of the first set, and K is the size of the result set.
 Since:
 6.2.0
This command is similar to ZDIFFSTORE
, but instead of storing the resulting
sorted set, it is returned to the client.
Examples
127.0.0.1:6379> ZADD zset1 1 "one"
(integer) 1
127.0.0.1:6379> ZADD zset1 2 "two"
(integer) 1
127.0.0.1:6379> ZADD zset1 3 "three"
(integer) 1
127.0.0.1:6379> ZADD zset2 1 "one"
(integer) 1
127.0.0.1:6379> ZADD zset2 2 "two"
(integer) 1
127.0.0.1:6379> ZDIFF 2 zset1 zset2
1) "three"
127.0.0.1:6379> ZDIFF 2 zset1 zset2 WITHSCORES
1) "three"
2) "3"