This command is similar to ZINTER, but instead of returning the result set, it returns just the cardinality of the result.
Keys that do not exist are considered to be empty sets. With one of the keys being an empty set, the resulting set is also empty (since set intersection with an empty set always results in an empty set).
Integer reply: the number of elements in the resulting intersection.
(integer) 1redis> ZADD zset1 2 "two"
(integer) 1redis> ZADD zset2 1 "one"
(integer) 1redis> ZADD zset2 2 "two"
(integer) 1redis> ZADD zset2 3 "three"
(integer) 1redis> ZINTER 2 zset1 zset2
1) "one" 2) "two"redis> ZINTERCARD 2 zset1 zset2
ERR Don't know what to do for "zintercard"