sunionstore

sunionstore(set union store 将两个集合的并集，保存到新的集合中，返回的是并集元素个数

127.0.0.1:6379> smembers set1
1) "1"
2) "2"
3) "3"
4) "4"
127.0.0.1:6379> smembers set2
1) "1"
2) "2"
3) "3"
4) "4"
127.0.0.1:6379> sunionstore destination set1 set2
(integer) 4 并集中一共有4个元素
127.0.0.1:6379> smembers destination
1) "1"
2) "2"
3) "3"
4) "4"
--------------------------------------------------------------
127.0.0.1:6379> smembers set5
(empty list or set)
127.0.0.1:6379> smembers set6
(empty list or set)
127.0.0.1:6379> sunionstore destination set5 set6
(integer) 0 并集元素0个
127.0.0.1:6379> smembers destination
(empty list or set)