set可以理解为无序集合
//插入一个值到集合 sadd key member
//查看集合的长度 scard key
//判断集合是否存在某个值
//返回 1或0 sismember key member
//删除集合的某个值
//返回 1或0
srem key member
set可以理解为无序集合
//插入一个值到集合 sadd key member
//查看集合的长度 scard key
//判断集合是否存在某个值
//返回 1或0 sismember key member
//删除集合的某个值
//返回 1或0
srem key member