Set类型是一个没有排序的集合，可以在该类型那个执行添加、删除或判断某一元素是否存在等操作。由于Redis的内部是使用值为空的hash table实现的，所以操作的时间复杂度为O(1), 最多存储2^32-1个字符串。
Set集合中不允许出现重复的元素，和List类型相比，Set类型在功能上另一个优势是可以进行并集，交集，差集运算。
sadd
129.223.248.154:6379> sadd students tim (integer) 1 129.223.248.154:6379> sadd students tim ben (integer) 1
srem
129.223.248.154:6379> srem student tim (integer) 0 129.223.248.154:6379> srem students tim (integer) 1
smembers、sismember
129.223.248.154:6379> smembers students 1) "ben" 129.223.248.154:6379> sismember students ben (integer) 1 129.223.248.154:6379> sismember students tim (integer) 0
sdiff 差集
129.223.248.154:6379> sadd setDiffA 1 2 3 (integer) 3 129.223.248.154:6379> sadd setDiffB 2 3 4 (integer) 3 129.223.248.154:6379> sdiff setDiffA setDiffB 1) "1"
sinter 交集
129.223.248.154:6379> sadd setInterA 1 2 3 (integer) 3 129.223.248.154:6379> sadd setInterB 2 3 4 (integer) 3 129.223.248.154:6379> sinter setInterA setInterB 1) "2" 2) "3"
sunion 并集
129.223.248.154:6379> sadd setUnionA 1 2 3 (integer) 3 129.223.248.154:6379> sadd setUnionB 2 4 6 (integer) 3 129.223.248.154:6379> sunion setUnionA setUnionB 1) "1" 2) "2" 3) "3" 4) "4" 5) "6"
scard 集合总数
129.223.248.154:6379> scard students (integer) 1 129.223.248.154:6379> smembers students 1) "ben" 129.223.248.154:6379> srandmember students "ben" 129.223.248.154:6379> sadd students mike (integer) 1 129.223.248.154:6379> srandmember students "ben" 129.223.248.154:6379> srandmember students "mike" 129.223.248.154:6379> srandmember students "mike" 129.223.248.154:6379> sadd memebrs a b c (integer) 3 129.223.248.154:6379> srandmember students 2 1) "ben" 2) "mike"
srandmember
129.223.248.154:6379> sadd letters a b c (integer) 3 129.223.248.154:6379> srandmember letters 2 1) "b" 2) "c"
spop
129.223.248.154:6379> spop letters "b" 129.223.248.154:6379> smembers letters 1) "a" 2) "c" 129.223.248.154:6379>
