该命令类似于 SDIFF, 不同之处在于该命令不返回结果集，而是将结果存放在destination集合中.

如果destination已经存在, 则将其覆盖重写.

返回值

integer-reply: 结果集元素的个数.

例子

redis> SADD key1 "a"
(integer) 1
redis> SADD key1 "b"
(integer) 1
redis> SADD key1 "c"
(integer) 1
redis> SADD key2 "c"
(integer) 1
redis> SADD key2 "d"
(integer) 1
redis> SADD key2 "e"
(integer) 1
redis> SDIFFSTORE key key1 key2
(integer) 2
redis> SMEMBERS key
1) "b"
2) "a"
redis>